Red Hat 6.1 Web Application Framework WAF Developer Guide

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Red Hat Web Application
Framework 6.1
WAF Developer Guide
Red Hat Web Application Framework 6.1: WAF Developer Guide
Copyright &copy; 2004 by Red Hat, Inc.
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rhea-dg-waf-en(EN)-6.1-Print-RHI (2004-03-29-T16:20-0800)
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Table of Contents
Introduction to the WAF Developer Guide........................................................................................ i
1. Assumptions About WAF Developers ................................................................................... i
2. Document Conventions.......................................................................................................... i
3. Code Presentation Conventions ........................................................................................... iv
I. WAF Concepts .................................................................................................................................. i
1. WAF Overview ..................................................................................................................... 1
1.1. General Architecture.............................................................................................. 2
1.2. Features .................................................................................................................. 3
1.3. Applications ........................................................................................................... 6
2. WAF Component: Persistence .............................................................................................. 9
2.1. Persistence Overview ............................................................................................. 9
2.2. Object-Relational Mapping.................................................................................... 9
2.3. Persistence Definition Language (PDL) ................................................................ 9
2.4. Persistence and Domain APIs (DataObject, DataAssociation, DataCollection,
DomainObjects) .............................................................................................. 10
2.5. Session and Transaction Management................................................................. 10
3. WAF Component: Kernel.................................................................................................... 11
3.1. Users and Groups................................................................................................. 11
3.2. ACSObject ........................................................................................................... 11
3.3. Permissions .......................................................................................................... 11
3.4. Kernel Resources ................................................................................................. 12
4. WAF Component: Services................................................................................................. 13
4.1. Auditing Service .................................................................................................. 13
4.2. Categorization Service ......................................................................................... 13
4.3. Formbuilder Service............................................................................................. 14
4.4. Globalization Service........................................................................................... 15
4.5. Mail Service ......................................................................................................... 16
4.6. Messaging Service ............................................................................................... 16
4.7. Notification Service ............................................................................................. 17
4.8. Portal Service ....................................................................................................... 17
4.9. Search Service...................................................................................................... 17
4.10. Workflow Service............................................................................................... 17
4.11. Versioning Service ............................................................................................. 18
5. WAF Component: Presentation........................................................................................... 19
5.1. Overview of Presentation Standards .................................................................... 19
5.2. CSS and XSLT ..................................................................................................... 20
5.3. JavaServer Pages (JSP) ........................................................................................ 24
5.4. Bebop - Reusable Web UI Components .............................................................. 25
6. WAF Component: Web ....................................................................................................... 31
6.1. Applications ......................................................................................................... 31
6.2. BaseServlet ...................................................................................................... 31
6.3. Dispatcher ............................................................................................................ 32
II. Equipping Developers.................................................................................................................. 33
7. Developing with WAF ........................................................................................................ 35
7.1. Developer Education............................................................................................ 35
7.2. Third-Party Development Tools........................................................................... 35
7.3. Developer Support ............................................................................................... 36
7.4. Setting Up Eclipse and WAF ............................................................................... 38
7.5. Using logging for debugging ............................................................................... 42
8. WAF Application Development Tutorial ............................................................................ 49
8.1. Terms and Assumptions ....................................................................................... 49
8.2. Good Practices ..................................................................................................... 49
8.3. Directories in the Work Area ............................................................................... 49
8.4. Build Tools........................................................................................................... 50
8.5. Modeling Your Application ................................................................................. 50
8.6. Persistent Object Types........................................................................................ 51
8.7. Java Domain Objects ........................................................................................... 51
8.8. Initializing the Application Runtime Environment.............................................. 57
8.9. Creating a Web Interface...................................................................................... 58
8.10. Integrating Your Package With CCM Tools ...................................................... 59
8.11. Creating Upgrade Scripts................................................................................... 60
9. Persistence Tutorial............................................................................................................. 63
9.1. Data Objects Tutorial ........................................................................................... 63
9.2. Beginning With Data Objects .............................................................................. 63
9.3. Associations ......................................................................................................... 70
9.4. Named SQL Events.............................................................................................. 74
9.5. Filtering, Ordering, and Binding Parameters ....................................................... 79
9.6. Common Mistakes ............................................................................................... 88
9.7. Transaction Management..................................................................................... 90
9.8. Link Attributes ..................................................................................................... 91
9.9. Dynamic Object Types......................................................................................... 96
9.10. Frequently Asked Questions .............................................................................. 97
10. Kernel Tutorial ................................................................................................................ 103
10.1. Permissions Tutorial ........................................................................................ 103
10.2. Domain Objects Tutorial.................................................................................. 106
10.3. Security Service FAQ....................................................................................... 118
10.4. Extending the Authentication System.............................................................. 121
11. Services Tutorials............................................................................................................ 123
11.1. Categorization Tutorial .................................................................................... 123
11.2. Categorization Scenarios ................................................................................. 126
11.3. Notification Tutorial......................................................................................... 132
11.4. Workflow Tutorial ............................................................................................ 135
11.5. Versioning Tutorial .......................................................................................... 138
11.6. Search Tutorial ................................................................................................. 146
12. Presentation (Bebop) Tutorial ......................................................................................... 153
12.1. Calling XSLT from a WAF Application .......................................................... 153
12.2. Handling Pre-Formatted Text........................................................................... 153
12.3. Site-Wide Master Pages ................................................................................... 154
12.4. Varying a Shared Layout.................................................................................. 158
12.5. Special-Case Stylesheets.................................................................................. 159
12.6. UI Tutorial........................................................................................................ 160
12.7. Working With Formbuilder .............................................................................. 161
13. Web Applications Tutorial .............................................................................................. 165
13.1. Support for Globalization ................................................................................ 165
13.2. Locale Negotiation........................................................................................... 165
13.3. ResourceBundles and MessageCatalogs.......................................................... 166
13.4. Accessing Resources........................................................................................ 167
13.5. Globalization and Bebop.................................................................................. 169
13.6. Localizing Stylesheets ..................................................................................... 170
13.7. Sending Mail Messages ................................................................................... 170
14. References .................................................................................................................................. 173
III. Appendixes ................................................................................................................................ 175
A. Bebop Tag Library Reference .......................................................................................... 177
A.1. Bebop/JSP ......................................................................................................... 177
A.2. Available Page Definition Tags ......................................................................... 177
B. PL/SQL Standards............................................................................................................ 181
B.1. General .............................................................................................................. 181
B.2. Coding Standards .............................................................................................. 181
B.3. Coding Style...................................................................................................... 183
B.4. Constraint Naming Standards............................................................................ 183
C. Java Standards .................................................................................................................. 187
C.1. WAF Standards.................................................................................................. 187
C.2. Java Coding Standards — References and Related Reading ............................ 188
D. PDL Syntax ...................................................................................................................... 189
D.1. PDL Grammar................................................................................................... 189
D.2. PDL Reserved Words........................................................................................ 191
D.3. PDL and SQL Used in the Tutorial................................................................... 194
Persistence Glossary ............................................................................................................. 203
Index................................................................................................................................................. 209
Colophon.......................................................................................................................................... 215
Introduction to the WAF Developer Guide
The Red Hat Web Application Framework is a platform for writing database-backed web applications
in Sun’s Java&reg;. Applications leverage Web Application Framework APIs to enable the authoring of
persistent structured data and to retrieve and display the data as content. The framework also integrates
services such as search, versioning, and permissions into its basic objects, enabling applications to
leverage framework services with little or no extra work.
The Web Application Framework domain layer models basic concepts such as users, groups, and
permissions and has been proven and refined on hundreds of production deployments. A user interface
(UI) framework, UI component library designed for the rapid development and reuse of web user
interfaces, and a powerful object-relational persistence engine are also part of the framework.
Please enjoy this guide and report any bugs with the documentation to http://bugzilla.redhat.com/.
Please report using the unique component name for this guide:
rhea-dg-waf-en(EN)-6.1-Print-RHI (2004-03-29-T16:20-0800)
1. Assumptions About WAF Developers
This manual assumes that the reader is familiar with the Java programming language, HTML, and
relational databases. Familiarity with the J2EE Servlet and JSP specifications, XML, and XSLT are
also helpful. An understanding of the UML and basic object-relational mapping concepts will help the
reader understand the persistence system. For more information, see Section 7.1 Developer Education.
2. Document Conventions
When you read this manual, certain words are represented in different fonts, typefaces, sizes, and
weights. This highlighting is systematic; different words are represented in the same style to indicate
their inclusion in a specific category. The types of words that are represented this way include the
following:
command
Linux commands (and other operating system commands, when used) are represented this way.
This style should indicate to you that you can type the word or phrase on the command line
and press [Enter] to invoke a command. Sometimes a command contains words that would be
displayed in a different style on their own (such as file names). In these cases, they are considered
to be part of the command, so the entire phrase is displayed as a command. For example:
Use the cat testfile command to view the contents of a file, named testfile, in the current
working directory.
file name
File names, directory names, paths, and RPM package names are represented this way. This style
should indicate that a particular file or directory exists by that name on your system. Examples:
The .bashrc file in your home directory contains bash shell definitions and aliases for your own
use.
The /etc/fstab file contains information about different system devices and file systems.
Install the webalizer RPM if you want to use a Web server log file analysis program.
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Introduction to the WAF Developer Guide
application
This style indicates that the program is an end-user application (as opposed to system software).
For example:
Use Mozilla to browse the Web.
[key]
A key on the keyboard is shown in this style. For example:
To use [Tab] completion, type in a character and then press the [Tab] key. Your terminal displays
the list of files in the directory that start with that letter.
[key]-[combination]
A combination of keystrokes is represented in this way. For example:
The [Ctrl]-[Alt]-[Backspace] key combination exits your graphical session and return you to the
graphical login screen or the console.
text found on a GUI interface
A title, word, or phrase found on a GUI interface screen or window is shown in this style. Text
shown in this style is being used to identify a particular GUI screen or an element on a GUI
screen (such as text associated with a checkbox or field). Example:
Select the Require Password checkbox if you would like your screensaver to require a password
before stopping.
top level of a menu on a GUI screen or window
A word in this style indicates that the word is the top level of a pulldown menu. If you click on
the word on the GUI screen, the rest of the menu should appear. For example:
Under File on a GNOME terminal, the New Tab option allows you to open multiple shell
prompts in the same window.
If you need to type in a sequence of commands from a GUI menu, they are shown like the
following example:
Go to Main Menu Button (on the Panel) =&gt; Programming =&gt; Emacs to start the Emacs text
editor.
button on a GUI screen or window
This style indicates that the text can be found on a clickable button on a GUI screen. For example:
Click on the Back button to return to the webpage you last viewed.
computer output
Text in this style indicates text displayed to a shell prompt such as error messages and responses
to commands. For example:
The ls command displays the contents of a directory. For example:
Desktop
Mail
about.html
backupfiles
logs
mail
paulwesterberg.png
reports
The output returned in response to the command (in this case, the contents of the directory) is
shown in this style.
prompt
A prompt, which is a computer’s way of signifying that it is ready for you to input something, is
shown in this style. Examples:
Introduction to the WAF Developer Guide
iii
$
#
[stephen@maturin stephen]$
leopard login:
user input
Text that the user has to type, either on the command line, or into a text box on a GUI screen, is
displayed in this style. In the following example, text is displayed in this style:
To boot your system into the text based installation program, you must type in the text command at the boot: prompt.
replaceable
Text used for examples which is meant to be replaced with data provided by the user is displayed
in this style. In the following example, version-number is displayed in this style:
The directory for the kernel source is /usr/src/ version-number /, where
number is the version of the kernel installed on this system.
version-
Additionally, we use several different strategies to draw your attention to certain pieces of information. In order of how critical the information is to your system, these items are marked as note, tip,
important, caution, or a warning. For example:
Note
Remember that Linux is case sensitive. In other words, a rose is not a ROSE is not a rOsE.
Tip
The directory /usr/share/doc/ contains additional documentation for packages installed on your
system.
Important
If you modify the DHCP configuration file, the changes will not take effect until you restart the DHCP
daemon.
Caution
Do not perform routine tasks as root — use a regular user account unless you need to use the root
account for system administration tasks.
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Introduction to the WAF Developer Guide
Warning
Be careful to remove only the necessary Red Hat Applications partitions. Removing other partitions
could result in data loss or a corrupted system environment.
3. Code Presentation Conventions
In addition to the standard document conventions covered in Section 2 Document Conventions, there
are some additional conventions related specifically to discussing source code:
classname
This is the name of a class in an object-oriented (OO) programming language. For example, the
class com.arsdigita.categorization.CategoryTreeNode.
method name
This is the name of a method in an OO programming language, e.g. the method getBase-
DataObjectType.
function
The name of a function or subroutine, as in a programming language. For example, the function
SecurityLogger.warn().
variable name
The name of a variable. For example, the variable BASE_DATA_OBJECT_TYPE.
option
An option for a software command or Method. For example, a user has been granted read
privileges on an object.
return value
The value returned by a function. For example, a method returns null.
replaceable
Content that may, must or will be replaced by the user or a program. For example, the code is
commented with NOTE(n), where n is the number of the NOTE.
program listing
A literal listing of all or part of a program. The \ character is used to break a line for printing
purposes. You will want to reconnect them back into a single line, preserving the spacing in the
line.
import
import
import
import
com.arsdigita.kernel.permissions.PermissionService;
com.arsdigita.kernel.permissions.PermissionDescriptor;
com.arsdigita.kernel.permissions.PrivilegeDescriptor;
com.arsdigita.persistence.OID;
OID acsObject = new OID(&quot;example.MyACSObject&quot;,
new BigDecimal(50));
OID party = new OID(&quot;com.arsdigita.kernel.Group&quot;, new BigDecimal(5));
Introduction to the WAF Developer Guide
v
PermissionDescriptor perm =
new PermissionDescriptor(PrivilegeDescriptor.READ,
acsObject, party);
PermissionService.grantPermission(perm);
first term
The first occurrence of a term, such as the first time we introduce a bulletin-board and note its
abbreviated form, bboard.
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Introduction to the WAF Developer Guide
I. WAF Concepts
This section covers the concepts of WAF. The intention is to provide both a very high-level architectural view and a closer review of the individual components.
Table of Contents
1. WAF Overview ................................................................................................................................ 1
2. WAF Component: Persistence ....................................................................................................... 9
3. WAF Component: Kernel............................................................................................................. 11
4. WAF Component: Services .......................................................................................................... 13
5. WAF Component: Presentation................................................................................................... 19
6. WAF Component: Web................................................................................................................. 31
Chapter 1.
WAF Overview
This chapter is an overview of the Web Application Framework architecture. This high-level viewpoint
is especially useful for gaining a good understanding of how WAF works. It is written with both the
technical developer and the technical manager/team leader in mind.
WAF is a web application development framework. Some of the web applications that have been
developed using WAF include Red Hat Content Management System and Red Hat Portal Server.
WAF runs in any standards-compliant servlet container. For more details about system requirements,
see the Red Hat Web Application Framework Installation Guide.
Figure 1-1 describes the architecture of WAF from a high-level perspective.
Figure 1-1. Basic Configuration
2
Chapter 1. WAF Overview
1.1. General Architecture
The WAF architecture described in Figure 1-1 follows the standard n-tier design pattern, with separate
presentation, domain (business logic), data, and data model layers. Web applications built on WAF
also follow the same n-tier design patter, leveraging the infrastructure provided by WAF.
1.1.1. The Layers
The four layers in the WAF architecture are:
•
Presentation Layer (UI) — presents information to the user
•
Domain Layer (Business Logic) — encapsulates business logic
•
Data Layer — stores and retrieves data
•
Data Model — stores data in a structured, format in a durable fashion
These layers are shown in Figure 1-2:
Figure 1-2. Basic Configuration
Chapter 1. WAF Overview
3
1.1.1.1. Presentation Layer
The Presentation Layer is responsible for presenting information to the end user. The presentation
layer accepts processed, structured data from the domain layer and is responsible for styling the data
appropriately and delivering the content in a format appropriate for the end user.
1.1.1.2. Domain Layer
The Domain Layer contains Domain Objects, which are abstractions of entities that exist in the business domain, for example, Party, Person, Group, Company, Department, Team, Product, Order, Line
Item.
1.1.1.3. Data Layer
The Data Layer contains two very important components:
Data Objects
Provide read and/or write access to the persistent properties of Domain Objects.
Persistence Metadata
Describes a Domain Object e.g., its name, its properties, and how each property is mapped into
the Data Storage layer. This description is written using the Persistence Definition Language
(PDL) format. PDL was designed to be used specifically in WAF. PDL is discussed in more
detail in Section 2.3 Persistence Definition Language (PDL).
1.1.1.4. Data Storage Layer
The data storage layer Contains the mechanism(s) employed for storing data persistently. This is
typically a relational database (RDBMS) such as Oracle9i™ database or PostgreSQL, combined with
a data model. It may also include other mechanisms, such as an LDAP directory or filesystem.
1.2. Features
In his seminal book Analysis Patterns, Martin Fowler writes that a framework “... should be applicable
across a large domain and be based on an effective conceptual model of that domain” (p. 11). Accordingly, the Web Application Framework defines a set of Domain Objects that are encountered in the
problem domain of most WAF applications. This object model further subdivides into two categories:
kernel and services.
In addition to kernel and services, WAF includes other features that facilitate building database-backed
web applications: infrastructure, persistence, presentation, and web.
1.2.1. Kernel
The kernel provides all the business logic provided by WAF, namely, business logic that is essential to building a web applications. Kernel provides domain objects that represent users, groups, and
permissions.
4
Chapter 1. WAF Overview
Figure 1-3. Basic Configuration
1.2.2. Services
Services are building blocks that address generic requirements common to most WAF applications.
Each requirement defines a set of related Domain Objects, for example, Versioning, Workflow, and
Categorization:
Chapter 1. WAF Overview
5
Figure 1-4. Basic Configuration
As shown in Figure 1-4, all services follow the n-tier design pattern discussed in Section 1.1 General
Architecture, providing:
•
A user interface for interacting with the Framework’s Domain Objects.
•
Domain logic.
•
The metadata (PDL) required for persistence of the Framework’s Domain Objects.
•
Data storage as appropriate.
Services are discussed in more detail in Chapter 4 WAF Component: Services.
6
Chapter 1. WAF Overview
1.2.3. Infrastructure
Infrastructure contains software to support the mechanics of application building at each layer of
the architecture (for example, serving page requests, styling the user interface, logging, specifying
metadata, storing data, etc.).
Note
This infrastructure exists independently from any specific problem domain and generally does not
depend on other WAF systems.
1.2.4. Persistence
Persistence handles the storage and retrieval of all information in WAF applications via Data Objects. Data Objects are implemented as a Java class library that supports CRUD (create, read, update,
and delete) operations for any type of Data Object. This is done through a set of generic interfaces:
DataObject, DataCollection, and DataAssociation. Persistence is discussed in detail in Chapter 2 WAF Component: Persistence.
1.2.5. Presentation
Presentation is responsible for presenting data in a structured format to the end user. WAF provides
three basic systems for presentation: Bebop, a web user interface component framework modeled
after Java Swing; Java Server Pages (JSP); and eXtensible Stylesheet Language (XSL). Presentation
is discussed in detail in Chapter 5 WAF Component: Presentation.
1.2.6. Web
The Web component of WAF makes the persistent data and domain logic of your application available
to others over protocols such as HTTP. It integrates the Java Servlet API and the kernel and persistence
components of WAF. For more information, see Chapter 6 WAF Component: Web.
1.3. Applications
Each WAF application adds code and other assets (stylesheets and PDL files) to each layer of the
architecture. The result is a complete application:
Chapter 1. WAF Overview
7
Figure 1-5. Basic Configuration
Again, each application follows the same n-tier design pattern, and builds upon the kernel and services
provided by WAF.
8
Chapter 1. WAF Overview
Chapter 2.
WAF Component: Persistence
This chapter discusses the persistence layer in the overall Web Application Framework. This was
originally discussed in Section 1.2.4 Persistence. You can find persistence tutorials in Chapter 9 Persistence Tutorial.
2.1. Persistence Overview
The storage and retrieval of persistent data is a common requirement of business applications. WAF
provides a persistence layer as a generic solution to this requirement.
The WAF persistence layer allows naturally written Java classes to be persisted to and queried from a
relational database. This is more than simply a method to save Java classes within the database. Developers can use the full range of standard object-oriented modeling techniques, such as inheritance,
interfaces, polymorphism, associations, and composition when writing their Java classes.
WAF persistence is an example of an object-relational mapping layer. This chapter will discuss some
of the concepts required to understand and use WAF persistence. Examples and tutorials are detailed
in Chapter 9 Persistence Tutorial.
2.2. Object-Relational Mapping
An object-relational mapping layer allows developers to use both relational and object modeling in
the development of their applications.
•
Relational Modeling — a powerful tool for modeling knowledge. Modern relational databases utilized with well designed relational schemas provide guaranteed data integrity, support for multiple
concurrent transactions, and support for fast and flexible querying.
•
Object modeling — a powerful tool for modeling behavior. Object modeling is useful when coupled
with object-oriented (OO) languages and design patterns. OO languages are a common choice for
rapid application development and maintenance.
An object-relational mapping layer can automatically translate operations on an object model into
operations on a relational model and vice versa. This is accomplished through the use of mapping metadata that relates persistent attributes and associations in the object model with tables and
columns in the relational model.
2.3. Persistence Definition Language (PDL)
Because of the flexibility of both relational and object models, it is possible to map a given object
model to many different relational models and to map a single relational model to many different
object models.
WAF persistence uses a modeling and mapping language called Persistence Definition Language
(PDL) to allow developers to describe their object model, their relational model, and how the two
are mapped.
The metadata described in PDL allows the relational engine to efficiently persist changes to the object
model and to construct efficient SQL queries for performing object-level reads. PDL also allows
developers to define their own custom queries and SQL operations to do specialized querying and
updating of the relational model.
10
Chapter 2. WAF Component: Persistence
For a listing of PDL terms, see Appendix D PDL Syntax. Examples of PDL usage can be found in
Chapter 9 Persistence Tutorial.
2.4. Persistence and Domain APIs (DataObject, DataAssociation,
DataCollection, DomainObjects)
Once an object model is described in PDL, the persistent state associated with it may be directly
accessed and manipulated by Java code through use of the DataObject, DataAssociation, and
DataCollection classes that are part of the WAF persistence API.
Developers can then build upon this API in order to add the behavior required to implement their application. This is generally done by extending DomainObject, an abstract base class that encapsulates
a DataObject and uses it to provide persistence capabilities to any derived classes.
2.5. Session and Transaction Management
Domain classes, once written, can be used similarly to any other Java code, with one exception — code
that involves domain objects must be executed within the context of both a session and a transaction.
The session identifies which database that changes are persisted to and queried from, and the transaction allows atomic updates of the database. Setup of the current session and transaction is a simple
process that can usually be centrally handled in an application.
Within WAF, session and transaction management is automatically handled by the BaseServlet
class. The transaction model used by WAF persistence is a simple extension of common relational
database transaction semantics:
•
Transactions cannot be nested.
•
Once a transaction begins it must either be committed or rolled back.
•
Transactions must be rolled back after an error occurs.
Chapter 3.
WAF Component: Kernel
This chapter discusses the kernel layer, which provides services used by several parts of the WAF
system. This component was initially explained in Section 1.2.1 Kernel. This discussion focuses on
the various parts of the kernel component which a developer will need in building for WAF.
For information on how to utilize the kernel in WAF applications, see Chapter 10 Kernel Tutorial.
3.1. Users and Groups
Applications have users. A user is a person who uses an application to accomplish some purpose.
In order to serve the needs of users, applications store information about the users. This information
is used to personalize content, check the permission of a user initiated operation, and to provide
information about a user to other users.
Users are organized into groups. The users in a groups are said to be members of the group. Groups
can also be members of groups. A group exists so that several users and groups can be collectively
identified as an entity.
Groups and users are the two types of parties. This parties system is one of the pieces of the kernel.
The ability to refer to an entity that may be a group or a user provides flexibility to application authors
in writing data models. An example is the definition of a group itself: 1 or more parties. This definition
is recursive, but that recursion reflects the flexibility of having a party type.
3.2. ACSObject
Party, Group, and User are all subtypes of ACSObject. Its purpose is to serve as a base class for use
in common object-level services, such as categorization and permissioning. As such, subclasses are
often types that users directly interact with such as Workflow or Category. The ACSObject object
type also has generic attributes such as a unique id and a displayName.
The ACSObject object type and class are abstract. In order to differentiate among subtypes there are
attributes objectType and defaultDomainClass. These attributes are used to instantiate the appropriate
Java domain class to wrap data objects that are instances of subtypes of ACSObject.
3.3. Permissions
The goal of the permissions system is to provide generic means to both programmers and site administrators to check, grant, or revoke permissions via a consistent interface. For example, an application
developer might decide that viewing a certain set of pages within the application is an operation to be
individually granted or revoked from a user. It’s expected that the permissions system will be heavily
used in production - almost every page will make at least one permissions API call, and some will
make several.
The permissions systems deals with three kinds of objects: ACSObject, Party, Privilege. The
system maintains a set of grants of the form Party p has Privilege priv on ACSObject obj. The
privileges represent actions that are performed on objects.
There are generic privileges that are always defined: read, write, edit, admin, create, and
delete. In addition, applications can define custom privileges, for example categorize.
The permissions system is used to answer questions such as:
12
•
Chapter 3. WAF Component: Kernel
What parties have a particular privilege on a particular object?
•
What privileges does a particular party have on a particular object?
•
On what objects does a particular party have a particular privilege?
Much of the power of the permissions system comes from the flexibility of the model. The assertions
described above are not the only input. Each privilege can imply some set of privileges. In addition,
each ACSObject can have a security context from which it inherits privilege grants. This security
context is just another ACSObject. Groups provide a way of aggregating users and the permissions
system pays attention to group membership.
The power of the permissions system comes from the interaction of these 3 hierarchies: group membership, security context, and privilege implication. Taking these 3 together, the assertion that p has
privilege priv on object obj means that p is a party or a member of a party (at any depth) that was
granted priv or a privilege implying privilege priv on object obj or any parent of obj in the security
context hierarchy.
3.4. Kernel Resources
Resource is a base class in the kernel that represents a user-accessible resource that may serve as a
data container. Resources are organized into a parent-child hierarchy. By default, resources set their
security context to their parent resource.
Currently, the two subclasses of resource are Application (which is web accessible) and Portlet
(which is accessible through Red Hat Portal Server). All Resources have a ResourceType which is
uniquely determined by the specific object type of the Resource. ResourceType has metadata that
is used by some generic navigation and administrative interfaces.
Chapter 4.
WAF Component: Services
WAF provides a number of generic services that can be used in developing a WAF application. Services leverage the business logic provided by the kernel, and provide specialized domain APIs to
solve specific, common business problems. Examples of services include notification, workflow, and
versioning.
Services were originally discussed in Section 1.2.2 Services. Implementation examples are covered in
Chapter 11 Services Tutorials.
4.1. Auditing Service
The auditing service can track when and by whom an object was created and last modified for an
ACSObject. This tracking is optional. The AuditedACSObject class provides methods for accessing
the auditing information.
4.2. Categorization Service
One common WAF application implementation is providing online access to large amounts of information. To make it easier for users to find relevant information, the categorization service is often
employed. It allows various pieces of information such as articles, forum postings, and so on, to be
categorized.
Categories are organized in a tree-like structure that is often called taxonomy or ontology. See Example
4-1.
14
•
•
Chapter 4. WAF Component: Services
Entertainment
•
Music
•
Movies
•
Television Shows
Education
•
•
Literacy
•
Testing
•
Home Schooling
•
Theories
Sports
•
Scores
•
Venues
•
Kinds of sports
•
Basketball
•
Chess
•
Soccer
Example 4-1. Sample Taxonomy
The categorization service provides:
•
The ability to set up multiple independent taxonomies.
•
A system for importing predefined taxonomies from XML files.
•
A user interface for managing categories.
•
An API for categorizing objects.
4.3. Formbuilder Service
Most applications built with WAF allow users to enter information into the system through a web
browser. A user fills out a number of fields in a form and clicks the Submit button. The user’s input
is validated and stored for later retrieval and display.
Building complex applications with this sort of user interaction usually requires programmer involvement. For example, if you are building a web browser based email client, you need to write code that
knows how to send and retrieve email messages, how to organize messages in folders, and so forth.
There are another class of applications that do not require any special handling of the input data. What
is required is the ability to enter the data in a structured way, and retrieve it later for display, reporting,
printing and so forth.
For example, a group of users wants to input and store data about competing products — they want
to record the product name, the company’s name, a short product description, and the date it was first
Chapter 4. WAF Component: Services
15
introduced to the market. Rather than requiring programming for this straightforward functionality,
WAF provides the formbuilder service.
The formbuilder service enables non-technical users to build such applications via a web interface, without any programmer intervention. The formbuilder service provides a variety of widgets
to choose from, such as a date widget which makes the part of the HTML form that allows you to
specify a date. Validation code is automatically attached to the date widget to ensure that only valid
dates are entered. Various widgets are provided for entering simple strings, numbers, etc.
Once the user has defined the required fields for their custom new document type, the system automatically allocates structured storage in the database. From this point on, other users may enter documents
that require the specified fields to be filled in. Such documents are displayed in the tabular format:
Product name
gizmo
Company name
Acme, Inc.
Description
This gizmo slices, dices, and juliennes.
Date introduced
July 22, 1999
Table 4-1. Sample structured document
4.4. Globalization Service
A globalized application is one that tries to equally accommodate readers of different languages and
dialects. Elements of the application’s user interface are shown in the user’s preferred language, if it is
supported. For example, a link to the categories page is displayed as Categories for English speakers
and Kategorien for German speakers.
A partial list of globalization and localization facilities supported by the Java language includes:
•
The notion of locale (http://java.sun.com/j2se/1.3/docs/api/java/util/Locale.html).
•
Resource bundles (http://java.sun.com/j2se/1.3/docs/api/java/util/ResourceBundle.html) allow you
to organize and maintain locale-specific objects, such as strings to be shown as button labels, e.g.
Categories and Kategorien.
•
Locale-specific date format (http://java.sun.com/j2se/1.3/docs/api/java/text/DateFormat.html\ #getDateInstance(int,java.util.Locale) — &quot;\&quot; has been inserted to show where the line was broken for
printing purposes; you will need to put both halves together again in e.g. your Web browser URL
window).
•
Locale-specific
collation
sequences of strings.
•
Miscellaneous other facilities.
(http://java.sun.com/j2se/1.3/docs/api/java/text/Collator.html)
of
The WAF globalization service provides classes and methods that can be roughly divided into the
following three categories.
1. Convenient wrappers around most-frequently used Java globalization APIs, such as resource
bundles.
2. Means of configuring the list of supported languages, locales, and character sets.
3. A mechanism for locale and character set negotiation.
Most modern browsers allow users to select their preferred language or a ranked sequence of
preferred languages. The globalization service looks at the user’s preferred language and locale,
16
Chapter 4. WAF Component: Services
as reported by the user’s browser, and compares them to the list of languages and locales that
the system is configured to support.
For example, a user can configure the preferred first language to be German (&quot;de&quot;) and the preferred second language to be British English (&quot;en_GB&quot;). If the system is configured to support
both of the languages, then the globalization service will choose &quot;de&quot; as the preferred locale.
If the system has been configured to support British English, but not German, then the globalization service will choose &quot;en_GB&quot; as the preferred locale. If the system does not support
either of the configured languages, then the service falls back to a default locale which could be
&quot;en_US&quot; (US English).
Once the desired locale is configured, a supported character set must be selected. For example,
pages in German can be displayed using the ISO-8859-1 1, UTF-8, or UTF-16 character sets.
The user may express a preference by configuring their browser. The user’s preference must
then be reconciled with the list of character sets that the system has been configured to support.
This example of locale and character set negotiation is simplified for this discussion, but it illustrates
the fact that correct negotiation is non-trivial. The globalization service relieves the developer of the
burden of negotiating the preferred locale and character set correctly.
The WAF globalization service provides a set of high-level APIs based on the standard Java globalization facilities that handle issues such as language negotiation and localization of static strings. These
APIs complement the basic globalization infrastructure provided by Java (i.e., ResourceBundles
and property files are still used in WAF) and are specifically designed for use by web applications
built with WAF.
4.5. Mail Service
The mail service acts as a Mail Transport Agent (MTA) for other WAF applications. It provides a
simple mechanism to send plain or rich text messages to any entity with a valid email address. This
service is not typically accessed directly, but rather is used as a building block for higher-level services
such as notification. This service has no dependencies on WAF and exists primarily as a wrapper for
the more cumbersome JavaMail API.
When should you use the mail service directly? If you are writing an application that sends simple
plain-text alerts to users, and you do not require those alerts to be recorded in the database, then it
makes sense to use the mail service. Also, if you are dealing with raw email addresses rather than
WAF parties (users and groups), you probably want to use the mail service directly. Otherwise, you
should consider using the higher-level notification service (see Section 4.7 Notification Service).
4.6. Messaging Service
The WAF messaging service is intended to be used as a building block for messaging applications,
which are WAF applications that use messages to represent various types of communication between
users.
Messages can represent an email from one user to another, or a bulletin-board post, or a comment on
another object in the system. A message can store attachments such as images or other files which are
relevant to the message. Each attachment can be of any arbitrary MIME type.
The implementation follows the RFC822 2 standard, which has been deprecated by RFC2822 3.
The Message class models a persistent text message with optional attachments:
1.
2.
3.
http://www.htmlhelp.com/reference/charset/
http://www.rfc-editor.org/rfc/rfc822.txt
http://www.rfc-editor.org/rfc/rfc2822.txt
Chapter 4. WAF Component: Services
17
1. The message body should have a MIME type of text/plain or text/html.
2. Each attachment to the message can have an arbitrary MIME type and format. Messages can
also refer to any ACSObject on the system.
MessageParts represent a message part (an attachment) in the sense of a multipart MIME message.
Each part has some content represented as an arbitrary block of bytes and a MIME type that identifies
the format of the content.
A ThreadedMessage is an extension of Message that allows messages to be organized into discussion threads with a tree structure. Messages at the first level are referred to as root messages.
Warning
If you delete the root message in a ThreadedMessage tree, all of its children are deleted.
4.7. Notification Service
The notification service is built on top of the mail and messaging services. Notification provides
persistent storage of messages, digest processing, automatic error recovery, and expansion of groups
into individual recipients.
Tip
When looking for a service to do alerting, consider the differences between the notification service
and the lower-level mail service. The mail API is capable of handling simple alerts in plain-text. If
you need added features, notification provides these.
4.8. Portal Service
The portal service provides basic domain classes that represent portlets and portals (a set of zero or
more portlets). The portal service is used by the Red Hat Portal Server and any WAF application that
provides portlets for displaying specific content to the end user.
For more information about utilizing portal services, see the Red Hat Portal Server Developer Guide.
4.9. Search Service
The search service provides APIs for indexing and searching content. Two search engines are supported by WAF: Oracle interMedia™ and Lucene. interMedia requires an Oracle database, while
Lucene is an open-source, database-independent search engine (see http://jakarta.apache.org/lucene/
for more information).
Objects that should be indexed register themselves with a SearchableObserver, which indexes the
object whenever the object is persisted. If you extend WAF with custom content types, making the
custom content searchable is a simple matter of implementing com.arsdigita.lucene.Adapter.
18
Chapter 4. WAF Component: Services
4.10. Workflow Service
Workflows allow specialized members of a group to collaborate using a standard process. Developers
can define new workflows using the workflow service.
A workflow contains a set of tasks, each of which may depend on one or more other tasks. A task is a
single unit of work. It can be enabled, disabled, or finished. A task may be assigned to a user or group.
Section 11.4.1 Simple Workflow describes the components of the simple workflow and how to create
workflows and assign them to users and groups.
4.11. Versioning Service
The goal of the the versioning system is to provide facilities for versioning data objects. This involves
recording information about changes made to the data in order to be able to:
1. Roll back to an earlier point in a data object’s history.
2. Undelete a data object (corollary of ability to perform rollback).
3. Compute the difference between any two versions of the data object.
To illustrate the last point, suppose you want to know the difference between the Jan 12 and Apr 19
versions of an article. The versioning service can tell you that the article’s title changed from Ravioli
is better than spaghetti to Macaroni is better than spaghetti, and its by-line changed from Guy Lewis
Steel to Guy Lewis Steele, Jr.
The service does not provide redundant storage. If you delete the versioned article in a context where
the versioning service is not available (either because it is turned off, or because you are manipulating
the database directly through JDBC or command-line client), there is no way for the versioning
service to restore it. It is not a substitute for regular database backups.
The service is provided transparently. There is very little that a developer has to do in order to make
their data versioned. To gain conceptual understanding of the versioning service, one must be familiar
with the key concepts of persistence: data objects and PDL (see Section 2.4 Persistence and Domain
APIs (DataObject, DataAssociation, DataCollection, DomainObjects), Section 2.3 Persistence Definition Language (PDL)). For a more detailed explanation of versioning, please refer to Section 11.5
Versioning Tutorial.
Chapter 5.
WAF Component: Presentation
Information in the database ultimately needs to be presented to the user for viewing and manipulating.
The Web Application Framework provides a variety of systems to display and style information. Each
system has its strengths and weaknesses, and is designed for specific situations.
The following sections discuss the various methods available for presentation under WAF. Each approach is designed to be complementary to the other approaches. Each approach is intended to be used
in different situations; the following sections discuss when each system should be used.
Presentation in the context of the Web Application Framework was originally discussed in Section
1.2.5 Presentation. For information about implementing Bebop, the presentation method unique to
Red Hat WAF, see Chapter 12 Presentation (Bebop) Tutorial. Further information and tutorials about
implementing the open standards presentation methods in WAF can be found through Chapter 14
References and on the Web.
5.1. Overview of Presentation Standards
This section discusses the standards used in WAF for textual presentation of structured data. In addition, the standard Java APIs for parsing and manipulating structured data are reviewed. This information is provided to set a common understanding of which tools are incorporated into WAF and how
they are used.
•
HyperText Markup Language (HTML) is the predominant web standard for rendering documents.
In WAF, HTML is produced either by JSPs or by transforming the XML generated by Bebop pages.
WAF applications use HTML in conjunction with the following technologies to render and style an
application’s output.
XHTML is the newest version of the HTML specification, adapted to conform to the standards of
XML.
•
Cascading Style Sheets (CSS) is a standard mechanism for adding presentation information (style
and layout) to HTML documents. See Section 5.2 CSS and XSLT for more information. WAF uses
CSS to style the HTML produced in JSPs and Bebop pages.
•
eXtensible Markup Language (XML) is a standard format for representing arbitrary tree-structured
data in textual format. XML documents appear similar to HTML because both are derived from
Standard Generalized Markup Language (SGML). WAF uses XML in its Bebop component UI
framework to describe a UI before it is styled.
•
Document Object Model (DOM) is an API (available in both C++ and Java) for manipulating an
XML document as a tree structure in memory. The heart of the DOM is the Node object, which
represents an element or attribute; a Document is the top-level object that represents an entire XML
document. WAF uses DOM to generate Bebop presentation XML. Bebop uses the J2EE JAXP API
to manipulate DOM documents.
•
eXtensible Stylesheet Language Transformations (XSLT) is a language for specifying rules to transform an XML document into some other kind of output. It is most often used for rendering XMLformatted data into an XML presentation format such as XHTML. WAF uses XSLT to convert
Bebop source XML into HTML for the client browser. Bebop uses the J2EE TrAX API to plug into
and use one of several available transformer implementations.
See Section 5.2 CSS and XSLT for more information about XSLT.
20
•
Chapter 5. WAF Component: Presentation
JavaServer Pages (JSP) is a J2EE standard for scripting dynamic web pages. JSPs typically produce
HTML, though they can generate any XML markup. WAF supports the use of JSPs as a primary
means of writing web UIs.
5.2. CSS and XSLT
WAF uses two technologies together, CSS and XSLT, to add style to logical (i.e. all form, no style)
markup.
•
CSS is used to control the style properties of HTML documents. CSS has broad browser support
and fine-grained control of properties such as color, borders and padding, positioning, and typeface.
Unlike XSLT, CSS cannot change the structure of the document it is styling. It cannot, for instance,
turn a bulleted list into a table.
Bebop uses CSS in the HTML that it produces when it transforms source Bebop XML. JSPs may
also use CSS. Consistent use of CSS under both regimes will give your site a more consistent look
and feel.
•
XSLT is used to transform the structure of an input document into a new and different structure on
output. This is very useful for creating modeling and then rendering UI concepts that do not exist
in HTML. A tabbed pane, for instance, is not part of the HTML standard, but a block of HTML
that functions as a tabbed pane can be produced by transforming source XML describing tabs into
a concrete HTML rendering.
Bebop, by design, produces XML that is not fit for direct consumption by a browser. Instead, it is
transformed first using XSLT. JSPs, by contrast, typically produce HTML directly and so will not
generally make use of XSLT. This is not, however, a rule. When it makes sense, a JSP author may
wish to produce XML and transform it using XSLT.
5.2.1. Integrating XSLT with WAF
WAF integrates XSL stylesheets in the following way:
•
It provides a default stylesheet as an integral part of each WAF package, so that each package ships
with some way to style the content it generates.
•
It allows the defaults for any package to be overridden when that package is invoked from a particular URL pattern. This allows for co-branding, etc.
•
It allows for special-usage page scripts (for example, JSP/XSL pairs) which can import site-wide
styling rules.
Note
WAF infrastructure depends on the Xalan-J XSLT engine from the Apache XML project. In turn, this
engine depends on the Xerces XML parser, also from Apache. Although it is theoretically possible to
use a different XML parser with Xalan, this process hasn’t been thoroughly tested. It is also possible
to use a different XSLT engine, such as Saxon. WAF contains no explicit dependency on any vendor’s
XSLT engine.
This flexibility comes from the PresentationManager interface, whose one method servePage
obtains a transformer for the current request, applies it to an input document, and serves the transformed output to the response output stream. A WAF application’s dispatcher can use the provided
Chapter 5. WAF Component: Presentation
21
BasePresentationManager or swap it out with its own to use a different algorithm for choosing a
stylesheet for the current request.
XSLT integration into WAF is accomplished by associating stylesheet documents with both WAF
packages and site nodes. A default stylesheet is associated with each WAF package, and the package
defaults can be overridden within a particular URL prefix’s scope. A site node represents a node in
the webapp’s URL tree; each site node, combined with its ancestors, generates a URL prefix. For the
purposes of this discussion, subsite is defined to mean any site node that contains child site nodes —
that is, a directory that contains subdirectories.
Because XSLT templates are also XML documents, they can be manipulated and composed dynamically. A PresentationManager could compute a new XSLT stylesheet on the fly, taking fragments
from files on disk or in the database.
For more information about using XSLT with WAF, see Section 12.1 Calling XSLT from a WAF
Application.
5.2.2. WAF Templating Package
The WAF Templating package (com.arsdigita.templating) serves as a repository for all classes relating
to the XSL templating.
5.2.2.1. Template Resolution
This section discusses the process of resolving the primary, top level stylesheet for transforming an
application’s XML DOM into an HTML page.
5.2.2.1.1. Background
The original
programmer
against its
override this
WAF method for resolving top level stylesheets required the application
to
register
a
default
com.arsdigita.kernel.StyleSheet
object
com.arsdigita.kernel.PackageType object. Project integrators could
default application stylesheet by registering a custom stylesheet against a
com.arsdigita.kernel.SiteNode object.
These mappings were maintained in the database and the rules for querying them to discover the
top level XSL template for an application were written into the standard presentation manager class
(com.arsdigita.sitenode.BasePresentationManager). This resulted in an XSL templating
architecture that was spread across multiple Java packages and left little scope for extending or altering
the template resolution algorithms, without massive code replacement / duplication.
5.2.2.1.2. Stylesheet Resolver
A quick analysis of XSLT usage across projects and applications shows that there are a large number
of variables that can come into play when deciding which stylesheet to apply to an application’s DOM.
Rather than attempt to standardize on a particular algorithm for resolving stylesheets, the WAF templating package introduces the com.arsdigita.templating.StylesheetResolver interface as
a means to plug in an arbitrary template resolution algorithm. This interface contains a single method:
public URL resolve(HttpServletRequest sreq);
This method may use any available state information to locate a stylesheet, which transforms XML
that has been generated during this supplied request object. The returned object must represent an
absolute URL under any protocol supported by the java.net.URL class (typically, either file:// or
http://). The com.arsdigita.templating.LegacyStylesheetResolver class provides a
resolver compatible with the resolution method used in WAF releases older than 6.0. The
22
Chapter 5. WAF Component: Presentation
com.arsdigita.templating.PatternStylesheetResolver class is the new preferred
resolver and now the default setting.
5.2.2.2. Pattern Based Resolution
The
primary
implementation
of
the
stylesheet
resolver
interface
is
the
class
com.arsdigita.templating.PatternStylesheetResolver. The core idea behind this
approach is that there is a list of abstract paths containing placeholders, of the form ::key::. For
example, a simplified version of the default list of paths looks like:
/__ccm__/apps/::application::/xsl/::url::-::locale::.xsl
/__ccm__/apps/::application::/xsl/::url::.xsl
When resolving which stylesheet to apply, the placeholders are expanded based on the request state,
to generate a list of real paths. Since a placeholder potentially has multiple valid values for a request, a
single abstract path could expand to multiple real paths. Placeholder expansion proceeds left-to-right,
to ensure a deterministic ordering of the list of real paths.
If
we
consider
an
example
request
for
the
content
/content/admin/index.jsp, the placeholder expansions might be:
• ::application:: • ::url:: -
section
admin
pages
at
(content-section)
(admin, index)
• ::locale:: -
(en_US, en)
If we proceed left-to-right with this expansion, the first expansion is for ::application::, leading
to:
/__ccm__/apps/content-section/xsl/::url::-::locale::.xsl
/__ccm__/apps/content-section/xsl/::url::.xsl
Next, the ::url:: placeholder is expanded:
/__ccm__/apps/content-section/xsl/admin-::locale::.xsl
/__ccm__/apps/content-section/xsl/admin.xsl
/__ccm__/apps/content-section/xsl/index-::locale::.xsl
/__ccm__/apps/content-section/xsl/index.xsl
Finally, the ::locale:: placeholder is expanded:
/__ccm__/apps/content-section/xsl/admin-en_US.xsl
/__ccm__/apps/content-section/xsl/admin-en.xsl
/__ccm__/apps/content-section/xsl/admin.xsl
/__ccm__/apps/content-section/xsl/index-en_US.xsl
/__ccm__/apps/content-section/xsl/index-en.xsl
/__ccm__/apps/content-section/xsl/index.xsl
Once all the placeholders have been expanded, these paths will be verified in order and the first
that exists returned as the primary stylesheet for the request. In this example the first match will
be /__ccm__/apps/content-section/xsl/admin.xsl.
Chapter 5. WAF Component: Presentation
23
5.2.2.3. Pattern Generators
The com.arsdigita.templating.PatternGenerator interface provides the mechanism for introducing new placeholders in the pattern based stylesheet resolver. This interface contains the single
method:
public String[] generateValues(String name,
HttpServletRequest request);
This method may use any available state information to generate a list of values for the placeholder.
The elements in the array should be ordered in decreasing specificity. If there are no possible values for
a placeholder, then an empty array can be returned, causing the entire abstract path to be thrown away.
As a hypothetical example, consider a pattern generator for switching based on the user’s browser:
public class BrowserPatternGenerator implements PatternGenerator {
public final static String GENERIC = &quot;generic&quot;;
public String[] generateValues(String key,
HttpServletRequest req) {
String useragent = req.getHeader(&quot;user-agent&quot;);
if (useragent != null &amp;&amp;
useragent.indexOf(&quot;MSIE&quot;)
-1) {
return new String[] { &quot;ie&quot;, GENERIC };
} elseif (useragent != null &amp;&amp;
useragent.indexOf(&quot;Mozilla&quot;)
-1) {
return new String[] { &quot;mozilla&quot;, GENERIC };
} else {
return new String[] { GENERIC };
}
}
}
Example 5-1. Web Browser Triggered Pattern Generator
Once the new pattern generator class has been implemented, it needs to be registered
with the resolver by calling the static registerPatternGenerator method in
com.arsdigita.templating.PatternStylesheetResolver, supplying the name of the
placeholder key. This registration is best done in the static initializer block of a core class, such as a
servlet.
static {
PatternStylesheetResolver.registerPatternGenerator(
&quot;browser&quot;,
new BrowserPatternGenerator()
);
}
Available Patterns
application
This pattern generator expands to the current application package key. ie, the value returned by a
call to com.arsdigita.web.Web.getConfig().getApplication().getKey().
host
This pattern generator expands to the hostname and port number for the current servlet container,
as returned by com.arsdigita.web.Web.getConfig().getHost().
24
Chapter 5. WAF Component: Presentation
locale
This pattern generator expands to the current kernel execution context locale. ie the value returned by a call to com.arsdigita.kernel.Kernel.getContext().getLocale();.
outputtype
If the outputType request parameter is set, this expands to one of text-plain,
text-javascript, or text-html if the parameter value is text/plain,
text/javascript or text/html respectively. In all other cases no values are generated.
prefix
If
the
current
request
has
passed
through
an
instance
of
the
com.arsdigita.web.InternalRedirectServlet, then this pattern generator expands to
the value of the prefix init parameter in the web.xml servlet declaration. In all other cases no
values are generated.
url
This pattern generator expands to multiple values based on the URL fragment remaining after the
application’s mount point. The set of values are generated by progressively stripping off trailing
path components. The values are then normalized as follows:
1. The file extension is removed.
2. Trailing occurrences of /index are replaced with /.
3. If the path is the empty string, it is replaces with index.
4. Occurrences of / are replaced with -.
Some examples are:
•
/index.jsp -
•
/-
{ &quot;index&quot; }
{ &quot;index&quot; }
•
/admin/index.jsp -
•
/admin/ -
•
/admin/item.jsp -
{ &quot;admin&quot;, &quot;index&quot; }
{ &quot;admin&quot;, &quot;index&quot; }
{ &quot;admin-item&quot;, &quot;admin&quot;, &quot;index&quot; }
5.2.2.4. Configuration
The choice of which stylesheet resolver to use is controlled by the waf.templating.stylesheet_resolver
property, and defaults to com.arsdigita.templating.PatternStylesheetResolver.
The location of the paths file to configure the pattern based stylesheet resolver is controlled by
the waf.templating.stylesheet_paths property, defaulting to /WEB-INF/resources/stylesheetpaths.txt
To enable an application to operate with the default pattern stylesheet resolver configuration,
its primary top level stylesheet should be named /__ccm__/apps/[application
key]/xsl/index.xsl.
Chapter 5. WAF Component: Presentation
25
5.3. JavaServer Pages (JSP)
JSP technology is a J2EE standard for presentation. JSP pages have full access to WAF APIs. For
documentation and tutorials on how to write JSPs, see http://java.sun.com/products/jsp/docs.html.
The strength of JSP is the ease with which a developer can rapidly develop and modify a single page.
JSPs can be recompiled on the fly, and changing layout is straightforward, since a JSP is patterned
after a standard HTML file. JSPs are recommended for projects where user interface specifications
rapidly change and where the need for UI reuse is limited.
JSPs that wish to use the services of the WAF framework must extend the base JSP servlet provided
by the WAF framework. See Section 6.2 BaseServlet.
5.4. Bebop - Reusable Web UI Components
Bebop is a web-based UI component framework. It is named after Swing™, the Java UI toolkit from
Sun.
Calling Bebop a web UI component framework has a very specific meaning:
•
Bebop as a framework is intended to establish a standard mechanism and pattern for defining UIs.
It is not a library of ready-to-wear UI elements, though it happens to include some.
•
Bebop as a component framework is used to define UIs, with the resulting components useful as UI
building blocks.
•
Bebop as a Web UI component framework — Bebop is specifically designed for the conventions
and constraints of the Web.
A component-based system is designed for reuse in varying contexts, bundles useful behaviors with
useful state, and operates in and responds to a service-rich environment. Bebop is intended to turn a
developer into a deployer by providing components which need only be told what to do, rather than
how to do it.
In Figure 5-1, Bebop components provide the tabbed pane. This tabbed pane component remembers
which are the currently visible components, and it knows internally how to generate the correct URLs
to other tabs. This functionality is gained just in using the component.
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Chapter 5. WAF Component: Presentation
Figure 5-1. Tabbed Pane Using Bebop Components
5.4.1. Working With Bebop
Chapter 12 Presentation (Bebop) Tutorial discusses specifics of implementing Bebop. This section is
a more abstract look into the design and usage of Bebop.
Bebop components follow these guidelines:
•
Provide a tree of components; components are also containers.
•
Consolidate parameter validation logic and support for custom validators.
•
Lock data structures for reuse across requests.
•
Automate state preservation and services to allow components to control their own state.
•
Multiplex Swing-like events onto the HTTP request.
•
For a given request, one component is selected and has control.
•
Transforms XML for global style; no HTML in Java strings.
The code in Example 5-2 gives an idea of how Bebop is used.
public void service(HttpServletRequest sreq, HttpServletResponse sresp) {
Page page = new Page(&quot;Content Section&quot;);
page.add(new Label(&quot;Content Section&quot;));
Chapter 5. WAF Component: Presentation
27
TabbedPane tabs = new TabbedPane();
page.add(tabs);
tabs.addTab(&quot;Browse&quot;, new BrowsePane());
tabs.addTab(&quot;Search&quot;, new SearchPane());
tabs.addTab(&quot;Roles&quot;, new RoleAdminPane());
page.lock();
Document doc = page.buildDocument(sreq, sresp);
transform(sreq, sresp, doc);
}
Example 5-2. Basic Bebop Page
5.4.1.1. Bebop Lifecycles
Bebop components used in a page design have a regular lifecycle.
UI Lifecycle
1. Register each component.
a. Each component adds any state parameters and event listeners it needs.
b. Each component is added to the page and given a unique key so that any state carried in
the query string is safe from collisions.
2. Lock the component tree.
a. Components can no longer be added or removed. The component instances are now safe
for reuse across requests.
3. Service requests.
Request Lifecycle
1. Client sends an HTTP request.
2. A new page state object is created.
Using the servlet request and the parameter models defined by the developer, the page builds an
object representing the state of the current request.
In addition to component state parameters, the selected component and the visibility state are
recovered from the servlet request state.
3. Fire the request event.
Any request listeners added when each component registered itself run at this time. Note that this
runs before the page request state is validated; in fact, the request event runs before much of any
work is done.
4. Validate page state.
This is when custom validators, e.g. a zip-code validation listener, are run. Parameters are also
typed at this step.
If there are errors, they are saved so that the component whose state is invalid may choose how to
present the issues.
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Chapter 5. WAF Component: Presentation
5. Fire the control event.
When a client sends a request to a Bebop page (e.g. a mouse-click on a tab); only one component
receives the request. This triggers the respond method of that component only; no other components response methods are involved.
If the request state is deemed valid, the selected component has the opportunity to respond, perhaps
changing the request state and thus the outcome of further processing.
A control event handles form submission, control links, and has influence on the state and visibility
before any output is produced.
6. Fire the action event.
The action event is an opportunity for any component to run code before the response is committed
and after the controlling component has responded.
Any component may listen and edit state and visibility before any output is produced. This is the
last opportunity to edit before XML is written out.
7. Generate XML.
The components generate the XML. They write to the document created in the first step. Each
component generates its own semantic XML (such as XUL, Mozilla’s presentation-based crossplatform markup language) and also delegates to its children. A DOM is built.
8. Transform the XML.
The XML document is transformed with an XSLT stylesheet and sent back to the client in the form
of HTML and CSS.
By following this method, it is easy to define and maintain a style and layout uniformity. A developer or designer can drop a different XSLT into the last step in a page request cycle.
9. The client receives the transformed results of the page request.
5.4.2. JSP Integration with Bebop
JSP is integrated with Bebop components (XML sources) and XSLT by using a JSP tag library to
allow the use of Bebop components in an otherwise standard JSP. The JSP tag libraries accomplish
this by performing transformations on the XML document produced by a Bebop page. This JSP tag
library also directs the generation of output by rendering the resulting XML document through XSLT,
so that the included components displayed in a JSP are styled with the standard template rules that are
used on the rest of the site. See Appendix A Bebop Tag Library Reference.
Java developers can also construct their Bebop pages in JSP. The tag library for declaring Bebop pages
is separate from the one for displaying Bebop components, but they are intended to work together. This
is different from using a Bebop component inside of JSP. In this instance, the specific Bebop JSP tags
takeover JSP similar to writing and controlling a servlet.
There are several motivating factors for integrating JSP with Bebop. First, laying out pages using JSP
integration will allow web developers who are not Java programmers to use third-party web publishing
tools (Dreamweaver, etc.) to alter the layout of pages, add new components to an existing page, edit
form field labels or prompts, etc. It would also be possible to make completely new pages with JSP
that display components from existing Bebop pages.
Second, JSP is a convenience for Java developers creating Bebop pages, because JSP shortens the
development cycle for individual pages by eliminating the need for a manual recompile and server
restart when a page is changed.
The overall request pipeline for constructing a page with Bebop and displaying it with JSP follows
this sequence:
Chapter 5. WAF Component: Presentation
29
1. The requested JSP obtains an XML document from a Bebop page object and the current request
state.
2. The tags in the requested JSP construct a new XML document, copying pieces from the Bebop
page where needed.
3. The resulting XML is passed as the XML input to an XSLT transformation step, using global
stylesheets.
4. The final result is sent to the user’s browser.
5.4.3. Relationship Between Static and Dynamic Pages
The JSP tag libraries for Bebop are designed to work together with Bebop’s model of static, shared
Page and Component objects, while providing familiar semantics to JSP authors. The division in
Bebop between static Page objects that produce dynamic output on each request is reflected by the
division of tags into two separate libraries:
A library of define:... tags.
Used for creating Bebop components.
The define:... tag library defines a Bebop page and its components with JSP tags. Since
the page structure may be static, JSP code in the define:... tag library is not guaranteed to
run on each request. Care must be taken to not put any runtime expressions or scriptlets into a
define:page block that are expected to run on each request.
A library of show:... tags.
Used for displaying the output form Bebop components inside a JSP page.
The show:.... tag library is dynamic. Any Java code inside a show:page block is guaranteed to run on each request, even if the components used are static. This is because the show:...
tags manipulate the XML output produced by Bebop components on each request, and not the
components themselves. Any valid JSP runtime expressions, tags, or scriptlets may be used in
conjunction with show:... tags and they should yield the same results they would in any other
JSP.
Caching in define:page can be suppressed with the JSP tag attribute cache=&quot;no&quot;. This will
cause the JSP define:page tag, along with the code and all the other tags inside it, to execute on
each request; the entire Page object will be re-created and garbage-collected on each request.
Warning
Although it seems there could be some benefit to changing the structure of a Page on each request,
it is not recommended.
Variations on the structure of a page will interfere with Bebop’s state maintenance, because the
URL and form variables that preserve state for individual components are linked to the component’s
position in the overall page structure. Runtime errors or unpredictable results may occur if a page’s
structure differs between subsequent requests.
Certain types of non-structural page variations between requests are permissible. Most importantly,
the individual options in option groups (radio groups, select widgets, checkbox groups) are not components themselves, so the following code is permissible:
define:radioGroup
% loop { %
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Chapter 5. WAF Component: Presentation
define:option label=&quot; %= rtexpr % &quot; value=&quot; %= expr % &quot;/
% } %
/define:radioGroup
This is especially true if the options in the group do not change frequently. Also, the contents of
stateless components (Labels, Links, Images, etc.) may change between requests, though the position
of the component in the page should not.
Further examples can be found at Appendix A Bebop Tag Library Reference.
Chapter 6.
WAF Component: Web
The Web component of WAF makes the persistent data and domain logic of your application available
to others over protocols such as HTTP. It integrates the Java Servlet API and the kernel and persistence
components of WAF.
For more information about building and deploying your own applications, see Chapter 8 WAF Application Development Tutorial.
6.1. Applications
WAF supports deploying multiple instances of an application type. A typical WAF installation may
have three forum instances, each with its own data and configuration at distinct locations on the site.
A WAF Application is the base on which developers build such applications in the WAF framework.
In the following, we distinguish between an application, here meaning the concrete application you
wish to develop, and Application, the WAF base class used to define such new applications.
6.1.1. Application Properties
Applications have a number of specific properties.
•
Applications are persistent — An Application has persistent properties describing its location,
name, etc. It is also a container of persistent data, often user-entered data, that a concrete application
uses to do its work. A forum, for instance, will contain database-stored message threads and posts.
•
Applications work with the dispatcher — Applications are designed to work together with the
WAF dispatcher to convert user-friendly URL paths into an application servlet and an application
instance containing its specific data. The dispatcher uses the location and parent properties of an
Application to look it up using the request URL.
•
Applications have a Servlet — Once the dispatcher has routed a request to an Application, the
Application responds using a Java Servlet.
•
Applications are associated with Stylesheets — The WAF presentation layer uses XSLT stylesheets
to implement the look-and-feel of its applications. The Application abstraction carries with it a
stylesheet property that the presentation layer uses to fetch the appropriate stylesheet.
•
Applications extend Resources — Applications leverage a feature of the WAF kernel API, Resources. Resources model containment, resource-partitioned user and configuration data, and a
data-backed type system. See Section 3.4 Kernel Resources. For example, Application uses the
containment behavior of Resource to implement its security.
6.2. BaseServlet
The WAF BaseServlet implements a Java Servlet and integrates it with the WAF kernel and persistence layers. The BaseServlet performs two functions:
•
Transaction management — The BaseServlet is responsible for starting and stopping the request’s database transaction. If any errors occur, the servlet will roll back the transaction. If application code requests a redirect, the BaseServlet ensures that the transaction is finished before
proceeding.
32
•
Chapter 6. WAF Component: Web
Request context — The BaseServlet packages certain facts about the request, such as the current
user, current application, etc., and loads them into a context object whose data is available to any
code running inside the servlet.
The BaseServlet is used in two principal ways in WAF:
•
New applications will sometimes use custom servlets that extend the BaseServlet and use the
Servlet API to implement their UI.
•
Applications that use JSPs can take advantage of the WAF platform by having their JSP pages
extend the BaseJSP class. Any code inside of the JSP will then be able to use the transaction and
request context setup by the BaseServlet.
6.3. Dispatcher
The WAF dispatcher connects user requests to Applications. A forum instance may live at
/apps/sales/forum/ while another is at /apps/engineering/forum/. The dispatcher maps
requests to the distinct Servlet and the distinct Application instance corresponding to each.
The design of the dispatcher is such that the URL-to-application mapping is reversible. Just as it is
possible to navigate from a URL to a specific data partition, it is possible to navigate from a data
partition back to a URL. This is done so that, given an object and its container, the WAF platform can
generate an address to it through the dispatcher.
A typical path through the dispatcher takes the following steps:
1. A request for the engineering forum at /apps/engineering/forum/index.html comes in.
2. The dispatcher is mapped to the pattern /apps/*, so the servlet container sends the request to the
dispatcher servlet.
3. The dispatcher servlet searches the database of applications using the path, minus the /apps prefix
and minus the filename suffix. The path /engineering/forum matches an Application instance
and the dispatcher servlet loads it.
4. The dispatcher servlet then fetches the path to the servlet of the application. The forum servlet is
mapped to /__ccm__/servlet/forum. The dispatcher forwards the request, now in the form
/__ccm__/servlet/forum/index.html.
5. The forum servlet receives the request. It uses application ID set on the request by the dispatcher
to load the data for the engineering forum. It uses the path info (in this case /index.html) part
of the request to display the appropriate page in the forum UI.
6. The engineering forum is served.
The WAF dispatcher is not responsible for serving static resources. Instead, your servlet container
in its default configuration performs the work of serving images, CSS and XSL files, and JSPs. No
special interaction with the dispatcher is necessary to use this feature of servlet containers.
II. Equipping Developers
This section provides information needed to develop on the Web Application Framework. Included
is a chapter on setting up a development environment and a number of tutorials related to the WAF
components.
Table of Contents
7. Developing with WAF ................................................................................................................... 35
8. WAF Application Development Tutorial..................................................................................... 49
9. Persistence Tutorial....................................................................................................................... 63
10. Kernel Tutorial .......................................................................................................................... 103
11. Services Tutorials ...................................................................................................................... 123
12. Presentation (Bebop) Tutorial.................................................................................................. 153
13. Web Applications Tutorial ....................................................................................................... 165
Chapter 7.
Developing with WAF
This chapter introduces prerequisites to working with WAF as well as the tools that are available to
the developer.
It is presumed that anyone developing for WAF has sufficient knowledge in his or her area of expertise
and can perform accordingly. For this reason, both high-level concepts, such as database design and
programming theory, and basic concepts, such as command line usage and shell scripting, are not
addressed.
7.1. Developer Education
A developer undertaking additions and modifications to this complex system needs a sufficient level
of appropriate knowledge. In particular, a developer should be knowledgeable and skillful in the following areas:
•
Java — the programming language used in WAF.
•
Servlets and JSP — the J2EE standards used in WAF.
•
SQL — used for directly accessing the relational databases in cases where the object-relational
mapping provided by the persistence engine is deemed insufficient.
•
UML — parts of the Unified Modeling Language’s basic vocabulary, especially those related to
class diagram, are used by the persistence framework.
•
XML and XSLT — key standards used in the WAF presentation system.
•
CSS — used to style WAF pages.
•
Concepts of Object Oriented (OO) programming.
•
Relational database design and object-relational mapping concepts.
In addition, a knowledge of Perl is necessary for extending the build system. PL/SQL and PL/pgSQL
are used to maintain certain denormalizations in the database.
A developer either needs to understand how to install, configure and administrate the chosen database
or have an experienced DBA performing those functions.
Finally, anyone who is involved with the installation, configuration and administration of the server(s)
and development environments for the WAF implementation requires sufficient skill in the target
installation OS, e.g. Red Hat Enterprise Linux AS.
Chapter 14 References contains references to additional resources that can help in understanding WAF.
7.2. Third-Party Development Tools
Tools are very straightforward. Because the WAF system is designed around open standards and open
source solutions, a developer is given a wide range of development tools and environments.
Programming is done primarily in Java, for which numerous Integrated Development Environments
(IDE) exist. One useful open source IDE is Eclipse. Integration of Eclipse with WAF is covered in
Section 7.4 Setting Up Eclipse and WAF. A developer can also use any text editor such as vi or Emacs.
For access to build systems and configuration files, either console or remote access to servers is required. The best choice for remote access is SSH, a protocol suite of network connectivity tools which
36
Chapter 7. Developing with WAF
includes a secure telnet replacement and a secure file-copy utility (scp). Both open source and proprietary implementations of SSH exist for virtually every OS. An open source implementation of SSH
for Unix-like systems can be found at http://www.openssh.org. The site also provides pointers for
various alternatives to OpenSSH.
The OpenSSH client is often packaged with the following Unix and Unix-like systems:
•
Linux
•
*BSD (FreeBSD, OpenBSD, NetBSD)
•
Apple OSX
•
Legacy Unices (Solaris, AIX, HP-UX, SCO, Irix, etc.)
For Win32 systems, a good open source application is PuTTY, found at
http://www.chiark.greenend.org.uk/~sgtatham/putty/. It is a Telnet/SSH client which also supports
sftp (secure ftp) and scp on a Win32 platform.
The ultimate output of WAF is HTML pages. These can be viewed in any modern Web browser.
For the most part, Web browsers will &quot;just work&quot;, although each browser may implement standards
differently.
For actual development efforts, it is highly recommended to use a version control system, also called
software control management (SCM). Several mature systems exist. On the open source side, there
is CVS (http://www.cvshome.org). The Red Hat Applications development teams use Perforce for
version control. If your code might integrate back into the main development tree, you may want to
look into Perforce at http://www.perforce.com.
7.3. Developer Support
WAF provides the Developer Support application to give developers high-level information about
each server request. Developer Support shows data such as request duration, number of queries, and
information about each query executed. In addition, Developer Support allows developers to adjust
their server logging level at runtime.
7.3.1. Enabling Developer Support
To enable Developer Support, edit your enterprise.init file and set the following initializer to
active:
init com.arsdigita.webdevsupport.Initializer {
active = true;
}
To disable Developer Support, modify your enterprise.init file and modify the webdevsupport Initializer so that active = false.
Once you have enabled Developer Support in your enterprise.init file, you must restart the
servlet container in order to use it. E.g. if you are using Tomcat, service tomcat restart is
sufficient.
Warning
You should always make sure that Developer Support is disabled in a production system. Developer
Support imposes a significant performance penalty on systems as it collects and stores request
debugging information.
Chapter 7. Developing with WAF
37
It is possible to have Developer Support enabled and not running. This still provides a measurable
performance hit because it registers a listener. Once enabled in enterprise.init and recognized
by the servlet container, you can turn Developer Support on and off via the administrator page. See
Section 7.3.2.2 Developer Support Features for more information on controlling Developer Support
via the administrator page.
7.3.2. Using Developer Support
7.3.2.1. Accessing Developer Support
To access Developer Support, login as a site-wide administrator and then navigate to /ds/ on your
server. For example, if your server is running on your localhost and your Dispatcher Servlet Path is
/ccm, then you would access Developer Support at http://localhost/ccm/ds/.
7.3.2.2. Developer Support Features
Once you have accessed Developer Support, you will find an index page listing up to the last 100
requests to the server as well as several options for configuring your server:
Request Information
Developer Support stores information about the last 100 requests to the server, accessible
through the index page. For each request, information such as the duration, the number of
database operations executed, the requesting IP address, and the URL requested is available.
This information is especially useful for performance-tuning. For example, if you are looking for
a slow or expensive page in a certain use case, look for a request with an unusually long duration
or large number of queries.
Click on a Request URL to find out detailed information about that individual request. The
Request Information page provides details such as the amount of time for various stages of the
request, and the text and duration of each SQL operation.
Click on a SQL Operation to find detailed information about that specific operation. The Query
Information page provides a stack trace showing the code that led to the SQL operation’s execution. Also, if the server is running on an appropriately configured Oracle database, the page
will provide a link to show the explain plan of the query.
Query Log
On the Developer Support index page, next to each request, is a link to a Query Log. A request’s
Query Log page presents a text page of all the SQL operations for that request, formatted for
easy cut-and-paste into a database client such as SQLPlus or PSQL.
Log4j Logger Adjuster
The Developer Support index page provides a link to a Log4j Logger Adjuster. This Log4j
adjuster allows the developer to change the server’s logging level at runtime. See also Section
7.5.1 Log4J
Disable Request Logging
The Disable Request Logging link on the Developer Support index page allows you to toggle
at runtime whether Developer Support actively stores information about each request. If you
disable request logging, Developer Support will clear all previously stored request information
as well as stop recording information about new requests.
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Chapter 7. Developing with WAF
Show Hits To Developer Support
The Show hits to developer support link on the Developer Support index page toggles the
tracking of requests against the Developer Support application itself. As most developers will
not be interested in this information, this information is usually left hidden.
7.4. Setting Up Eclipse and WAF
The following sections describes how to set up a WAF development and debugging environment
within Eclipse, an open source Integrated Development Environment (IDE).
7.4.1. Installing Eclipse
1. Install WAF — install as normal, using the RPM’s and WAF Autobuild system. For more information, see the Red Hat Web Application Framework Installation Guide:.
2. Install Eclipse — Eclipse can be obtained from http://www.eclipse.org. Install using RPM, if
possible.
In order to take advantage of the anti-aliased fonts within Eclipse, use a build of Eclipse designed
for the GTK in Red Hat Linux 8.0 and later.
3. You may also wish to install the Perforce, Resin, and JavaCC plugins for Eclipse, which can be
found at:
•
http://sourceforge.net/projects/p4eclipse
•
http://www.improve-technologies.com/alpha/resin
•
http://sourceforge.net/projects/eclipse-javacc
4. To install the Perforce and Resin plugins, use the Eclipse Update Manager by selecting Help =
Software Updates = Update Manager. Next, add bookmarks for the download URLs listed
by the plugins’ Web sites. The Update Manager can then automatically download and install the
Perforce and Resin plugins.
To install the JavaCC plugin, download the plugin and unzip it in Eclipse’s plugin directory. Then,
follow the instructions in the plugin’s README file.
5. Install Resin — if you are using the Resin application server. You may download Resin at Caucho’s website: http://caucho.com. You may also want to download the source code for Resin in
order to trace through its code when debugging.
7.4.2. Eclipse Preferences Configuration
To set preferences within Eclipse, go to Window =
•
Workbench =
•
Java = Compiler =
options:
Preferences. Noteworthy preferences include:
Editors. There is a key bindings option where you can select Emacs key bindings.
Errors and Warnings. You probably only want to select Error for the
•
Unreachable code
•
Resolvable import statements
Chapter 7. Developing with WAF
39
Tip
It is recommended to only select Warning for the options:
•
Methods overridden but not package visible
•
Methods with a constructor name
•
Hidden catch blocks
Otherwise, your compilations will output hundreds of messages in your Tasks window.
7.4.3. Eclipse Project Configuration
This section covers adding and configuring projects to Eclipse for developing with WAF.
7.4.3.1. Adding Projects
WAF
1. In Eclipse, go to File =
2. Select Java Project.
New =
Project.
3. Name the project, e.g. webapp and select your existing WAF core-platform directory as the
project directory.
4. In the source tab, make sure that Eclipse lists the WAF source directory, src/. If it is not
there, click Add Existing Folders... to add it. You may also want to add the directory for the
Junit test code, test/src/.
After adding the existing source folders, click on Create New Folder... and name the folder
_generated. This is where Eclipse will store its JavaCC-generated source files.
5. Select the Libraries tab once you are presented with the Java Settings dialog box.
6. Click on Add JARs and select all the JARs under your WAF Project (typically under lib
and etc/lib).
7. Click on Add External JARs and add the following JARs:
• $ORACLE_HOME/jdbc/lib/classes12.zip
• $RESIN_HOME/lib/jta-spec JAR
• $RESIN_HOME/lib/resin.jar
8. Click on the Order and Export tab. Select All.
9. Create a build folder for Eclipse on your file system. Then, enter the path to that build folder
in the Build output folder input box.
10. Click on the Finish button.
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Chapter 7. Developing with WAF
CMS and Other Projects
To add CMS or other projects to Eclipse, follow the same steps as for adding WAF, with the
following exceptions:
•
For CMS and other projects that depend on WAF, you do not need to add external JARs.
Eclipse will pick up these libraries from WAF.
•
When you reach the Java Settings dialog box, select the Projects tab. For CMS, add a dependency upon WAF. For projects that use both WAF and CMS, add a dependency upon both
WAF and CMS.
•
Create build folders for the respective projects.
7.4.3.2. Configuring Eclipse for Perforce
For each project that you have added, go to the Package Explorer and right-click on it. Then, select
Team = Share Project. Select the options for Perforce. Now, you should see a Perforce menu and
Perforce options for your source files.
7.4.3.3. Building and Deploying with Eclipse
Eclipse uses its own build directories for compiling your source files. However, you will probably still
want to use the WAF build system for building and deploying your application. Therefore, you should
create a shell script that will do this for you. Then, you may call this shell script to build and deploy
WAF from within Eclipse when you are ready to run your application.
Here is an example shell-script, which should be modified appropriately to fit the target environment.
#!/bin/bash
#setup environment
. /etc/profile.d/ccm-config.sh
. /etc/profile.d/ccm-devel.sh
. /etc/profile.d/ccm-scripts.sh
CCM_HOME=/var/ccm-devel/dev/user/cms_dev
ORACLE_HOME=&quot;/opt/oracle/product/9.2.0&quot;
JAVA_HOME=/opt/IBMJava2-131
CLASSPATH=$CCM_HOME/core-platform/lib/jaas.jar
CLASSPATH=$CLASSPATH:$CCM_HOME/core-platform/lib/jce.jar
CLASSPATH=$CLASSPATH:$CCM_HOME/core-platform/lib/sunjce_provider.jar
CLASSPATH=$CLASSPATH:$CLASSPATH:$ORACLE_HOME/jdbc/lib/classes12.zip
CLASSPATH=$CLASSPATH:$CCM_HOME/core-platform/etc/lib/iDoclet.jar
export CLASSPATH
export ANT_OPTS=&quot;-Xms128m -Xmx128m&quot;
##########
#build
##########
#uncomment to make enterprise.init
#cd $CCM_HOME
#ant make-config
#ant make-init
Chapter 7. Developing with WAF
41
#clean
cd $CCM_HOME
ant clean
#build
cd $CCM_HOME
ant deploy
#javadoc
cd $CCM_HOME
ant javadoc
ant deploy-api
Example 7-1. Shell-script to build and deploy from within Eclipse
In your ant.properties file, make sure that you have set compile.debug=on. Once you have
created this shell script, in Eclipse go to Run = External Tools = Configure. A dialog box will
appear for configuring external tools. Select New and in the Tool Location input box, select your
shell script for deploying WAF. Select the options:
• Block until tool terminates
• Show execution log on console
Then, select OK. Now, in Eclipse, your shell script will appear under Run =
that to build and deploy WAF from within Eclipse.
External Tools. Use
7.4.4. Eclipse Debugging Configuration
To do runtime debugging of WAF within Eclipse, you will need to add a new Resin launch configuration for running WAF and a new Remote Java Application debug configuration for attaching to
WAF.
WAF Execution Setup
To be able to run WAF from Eclipse, select Run =
Then, enter information for the following tabs:
•
Run. Select Resin and then click on New.
Main Tab
To set your project, select the highest-level project, which is the project no other projects are
dependent on. This is where you select your resin.conf.
•
Arguments Tab
In the VM arguments text box, enter the following, all in one line — this line is broken for
printing purposes with a &quot;\&quot;:
-Xdebug -Xnoagent -Djava.compiler=NONE -Xrunjdwp:transport=\
dt_socket, server=y, suspend=n,address=8000 -Xms128m -Xmx128m
You may allocate more memory than 128 MB to the server if you wish.
•
Classpath Tab
•
Common Tab
Add all the external JARs under $RESIN_HOME/lib to your user classes.
At the bottom of the dialog box, select Display in favorites menu: Run.
You are now finished and may close the dialog box.
42
Chapter 7. Developing with WAF
WAF Debugging Setup
In Eclipse, select Run = Debug. In the dialog box, select Remote Java Application and then
click on New. Then enter information for the following tabs:
•
Connect Tab
Enter a name for your debug configuration, such as webapp-debug. Select the same project
previously selected as the main project. Enter the host name (localhost should be fine). Use
8000 as your connection port. Also, select Allow termination of remote VM.
•
Source Tab
•
Common Tab
Add all the external JARs under $RESIN_HOME/lib to your source lookup path.
At the bottom of the dialog box, select Display in favorites menu: Debug.
You are now finished and may close the dialog box.
7.4.5. Eclipse Setup Validation
Your Eclipse setup should now be complete. To test this:
1. Select Run =
External Tools =
[Deploy Script].
2. Select Run = Run and pick the WAF configuration. The server’s log output should become
visible in the Console. Wait for the server to finish initializing.
3. Select Run = Debug and pick the debug configuration. This opens the Debug perspective.
Open a source file, set a breakpoint, and request a page from the server.
If everything is setup correctly, you can now develop with Eclipse and use it to step through your
WAF code.
7.5. Using logging for debugging
When code breaks, there are two ways to figure out what went wrong: launch a debugger and step
through the program, or add logging statements to see what is going on. In its crudest form, logging
means adding a few System.err.println() calls here and there. What are the benefits of logging
over using a debugger?
The Practice of Programming by Brian W. Kernighan and Rob Pike
As a personal choice, we tend not to use debuggers beyond getting a stack trace or the value of a variable
or two. One reason is that it is easy to get lost in details of complicated data structures and control flow;
we find stepping through a program less productive than thinking harder and adding output statements and
self-checking code at critical places. Clicking over statements takes longer than scanning the output of
judiciously-placed displays. It takes less time to decide where to put print statements than to single-step to
the critical section of code, even assuming we know where that is. More important, debugging statements
stay with the program; debugger sessions are transient.
Another important use of logging is to provide an audit trail: who did what and when. The predominant
pattern in WAF is to write such auditing information to the database rather than the filesystem. The
logging framework in WAF is intended to be used primarily for troubleshooting and debugging.
Chapter 7. Developing with WAF
43
7.5.1. Log4J
Using System.out.println() for logging has numerous drawbacks.
1. It degrades performance. There is no easy way to conditionally turn off logging statements
system-wide, without resorting to error-prone and maintenance-intensive workarounds such as:
if (DEBUG) {
System.err.println(&quot;foo=&quot; + foo);
}
where DEBUG is a system-wide boolean parameter that you can easily set to true or false.
2. Even with the above workaround, you don’t get a fine-grained degree of control. The logging is
either on, or off across the board. You could, of course, introduce more than one system-wide
flag, like so:
if (WARN) {
System.out.println(&quot;warn: bar=&quot; + bar);
}
3. You are constrained to outputting only to the standard out and error devices. What if you need
to output to rotated log files? Additional custom code is required to support this requirement.
Going down this path slowly but surely, you may end up developing a general-purpose logging library.
Rather than reinventing the wheel, WAF relies on the Log4J library from the Jakarta project of the
Apache Foundation. If you are not familiar with it, please skim through the online documentation at
http://jakarta.apache.org/log4j/docs/. The rest of this document tries to highlight rather than explain
the most salient Log4J features.
The key abstractions that Log4J provides are:
1. Ability to log to multiple devices. See the Javadoc for the Appender1 interface and its implementing subclasses. There are many types of appenders included in Log4J: file appender,
rolling file appender, remote syslog daemon appender, asynchronous appender, etc. Appenders
are fairly easy to extend for special purposes. For instance, you could write a database appender. (In fact, several have already been written.) See Section 7.5.4 Custom Appenders for more
discussion on this.
2. Ability to easily configure the format of the message. For example, each message can automatically include the timestamp, thread name, location (file name and line number), full or abbreviated class and method name from the which the message originated, etc. See the Javadoc for
Layout (at http://jakarta.apache.org/log4j/docs/api/org/apache/log4j/Layout.html) and its subclasses.
3. API for logging errors and exceptions. See Section 7.5.2 Always log the Throwable.
4. Different logging levels. The minimum set of possible levels are off, fatal, error, warn,
info, debug, and all. Extending the list of levels is possible but discouraged. You can change
the requested level of logging either by altering your configuration files before system startup,
or at runtime. More on this in Section 7.5.3 Runtime logging level manipulation. See also the
Javadoc for Level (http://jakarta.apache.org/log4j/docs/api/org/apache/log4j/Level.html).
5. Fine-grained hierarchy of loggers. A logger is the central class that performs all logging operations. Loggers are named with dot-delimited names like foo.bar.baz or foo.bar.quux.
Loggers form a hierarchy based on their names. You can configure and manipulate loggers in
bulk by referring to their parent names. For example, both foo.bar.baz or foo.bar.quux
are children of foo.bar.
Each logger has an associated logging level. By setting the logger’s level, you can control the
amount of information logged. Log statements are enabled only if the level of statement is
1.
http://jakarta.apache.org/log4j/docs/api/org/apache/log4j/Appender.html
44
Chapter 7. Developing with WAF
greater than or equal to the current level of the logger. For example, if you set the foo.bar.baz
logger’s level to warn, it will only log message whose level is warn, error, or fatal. By
setting the level for the foo.bar logger, you are automatically setting it for foo.bar.baz and
foo.bar.quux, unless overridden on a more specific level.
6. Miscellaneous other items such as filters2 and flexible configuration.
The next sections examine some of these benefits in more detail.
7.5.2. Always log the Throwable
In general, if you catch an exception and decide not to rethrow it for whatever reason, you should log
it. In doing so, avoid the following anti-pattern:
try {
doSomething();
} catch (FooException ex) {
ex.printStackTrace();
s_log.warn(&quot;foo occurred: &quot; + ex.getMessage());
}
Example 7-2. Exception logging anti-pattern
The printStackTrace() method should not be used, because its output goes to the standard error
device System.err rather than the devices managed by Log4J.
The getMessage() method should not be used, because it does not include the stack trace. Stack
traces are invaluable for tracking down the source of error conditions.
The following pattern should be used instead.
try {
doSomething();
} catch (FooException ex) {
s_log.debug(&quot;foo occurred&quot;, ex); // or
s_log.info(&quot;foo occurred&quot;, ex); // or
s_log.warn(&quot;foo occurred&quot;, ex); // or
s_log.log(Level.WARN, &quot;foo occurred&quot;, ex);
}
Example 7-3. Log the Throwable
Note that the various logging methods provided by the Logger 3 class all take a Throwable parameter,
i.e. an Error or Exception. Given a throwable, Log4J will print both the error message obtained via
getMessage() and the stack trace.
However, be careful not to fall into this trap:
2.
3.
http://jakarta.apache.org/log4j/docs/api/org/apache/log4j/spi/Filter.html
http://jakarta.apache.org/log4j/docs/api/org/apache/log4j/Logger.html
Chapter 7. Developing with WAF
45
try {
doSomething();
} catch (FooException ex) {
s_log.debug(ex);
}
Example 7-4. Swallowed stack trace anti-pattern
There is no debug(Throwable throwable) method — there is only debug(Object msg). Same
goes for warn, info, etc. The above statement is essentially equivalent to the following:
s_log.debug(String.valueOf(ex));
This is probably not the intended result.
What if you want to log the current stack trace? The easiest way to do this is to log a new Throwable:
s_log.debug(&quot;got here&quot;, new Throwable());
Example 7-5. Logging the current stack trace
A variation of this technique is to add a public Throwable field to a class.
public class Frob {
// add the following line temporarily
public final Throwable STACK = new Throwable();
}
Example 7-6. Tracking the origin of an object
Once this has been done, you can write code such as this:
class Foobar {
void doStuff(Frob frob) {
if ( !checksOutOK(frob) ) {
s_log.error(&quot;Got a sketchy frob&quot;, frob.STACK);
}
}
}
This allows you to figure the origin of the frob object at a distant point further down the execution
path.
7.5.3. Runtime logging level manipulation
Logging levels are usually configured at system startup via the configuration file. It is possible to
change the logger’s level at runtime. One way to do this is via the Developer Support interfaces. (See
Section 7.3 Developer Support.) From the programmatic point of view, runtime manipulation of the
logging level boils down to something as simple as this:
// assume s_log is instance of Logger
s_log.setLevel(Level.WARN);
This sets the logging level for the s_log logger to warn. This means that messages output via, say,
debug(Object msg, Throwable throwable) will be suppressed, because warn is stricter than
debug.
The standard pattern for instantiating loggers that is used throughout WAF is as follows:
46
Chapter 7. Developing with WAF
package foo.bar;
import org.apache.log4j.Logger;
public class Baz {
private final static Logger s_log = Logger.getLogger(Baz.class);
}
Example 7-7. Standard way of instantiating loggers
This instantiates a singleton logger named foo.bar.Baz. Note, however, that assigning the logger
to a private static variable is merely a matter of syntactic convenience. If you ever need to, you can
obtain the same logger from anywhere else in your code.
package foo.frob;
import org.apache.log4j.Logger;
class Nosey {
void doStuff() {
Logger logger = Logger.getLogger(&quot;foo.bar.Baz&quot;);
logger.debug(&quot;got the logger used by the Baz class.&quot;);
}
}
Example 7-8. Random access to loggers
There is a couple reasons why this might be useful.
1. This allows you to adjust the logging level of any logger at runtime. If you have a production
system that starts exhibiting erratic behavior, you can turn up the logging level in selected classes
without shutting down and restarting the system. This is what Developer Support allows you
to do.
2. There are times when you want to see what goes on in the class Foo when you call a method
reliant on Foo elsewhere in your code.
To
elaborate
on
the
last
point:
Consider
the
logging
output
generated
by
the
com.arsdigita.db.PreparedStatement logger. If the logging level for this logger is set to
info, it will log every executed query and its bind variable values. If you are interested in seeing the
query your code generates, you can set this logger’s level to info in your config file. Note, however,
that this will result in all queries being logged system-wide. That may be many more than you
require. The alternative is to adjust the logging level at runtime:
// assume all the necessary imports
class Frobnivator {
void frobnivate() {
Logger logger = Logger.getLogger(&quot;com.arsdigita.db.PreparedStatement&quot;);
Level old = logger.getLevel();
logger.setLevel(Level.INFO);
doSomething();
logger.setLevel(old);
}
Chapter 7. Developing with WAF
47
}
Example 7-9. Adjusting logging level temporarily
In the above example, you end up enabling the PreparedStatement logger only for the duration
of the doSomething() method. This may significantly cut down the number of queries logged, thus
making it easier for you to see what is going on.
The obvious caveat here is that extraneous queries may still end up getting logged in the presence of
multiple threads. This is because the logger’s level cannot be adjusted on a per-thread basis - it can
only be changed globally.
7.5.4. Custom Appenders
Out of the box, WAF provides two appenders: ConsoleAppender 4, wired to your standard output
device (usually a TTY), and RollingFileAppender 5 tied to a file whose location is configurable.
You can also use other appenders. One of the interesting possibilities is the SocketAppender 6. It
expects a log viewer (or some other log processing application) to listen on the specified TCP port,
possibly on a different machine. There are a number of GUI log viewers that work with the socket
appender. These viewers give you fine-grained control over your logging output. See, for example,
Chainsaw 7 and Lumbermill 8. Both of these log viewers allow you to filter the output by level,
logger, thread name, etc.
7.5.5. Beware of Buffered Streams
The Java language provides two abstractions for doing output: output streams 9 for working with
sequences of bytes, and writers 10 for working with sequences of characters. An output stream or a
writer can be buffered or unbuffered. For more information, read about BufferedOutputStream 11
and about BufferedWriter 12.
When I/O is buffered, it means that bytes or characters that you write do not necessarily go to their
intended output device immediately. They are cached in an intermediate buffer. When the buffer fills
up, it is flushed — an actual write to the underlying physical device occurs.
Why should you care about this? If you log a message to a buffered output immediately before the
system crashes, you may not see the message logged anywhere. The system didn’t have a chance
to flush the buffered stream or writer. This situation is fairly rare, but when it does happen, it may
stump the unwary troubleshooter. If you want to be absolutely sure you are not losing any logging
statements, you must use unbuffered output.
For example, the standard output System.out may be buffered, while the standard error device System.err is usually not. Therefore, System.err is preferable when you want to make sure no logging
is lost.
4.
5.
6.
7.
8.
9.
10.
11.
12.
http://jakarta.apache.org/log4j/docs/api/org/apache/log4j/ConsoleAppender.html
http://jakarta.apache.org/log4j/docs/api/org/apache/log4j/RollingFileAppender.html
http://jakarta.apache.org/log4j/docs/api/org/apache/log4j/net/SocketAppender.html
http://jakarta.apache.org/log4j/docs/api/org/apache/log4j/chainsaw/package-summary.html
http://traxel.com/lumbermill/
http://java.sun.com/j2se/1.3/docs/api/java/io/OutputStream.html
http://java.sun.com/j2se/1.3/docs/api/java/io/Writer.html
http://java.sun.com/j2se/1.3/docs/api/java/io/BufferedOutputStream.html
http://java.sun.com/j2se/1.3/docs/api/java/io/BufferedWriter.html.
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Chapter 7. Developing with WAF
What kind of I/O does log4j use: buffered or unbuffered? It depends on how the particular appender
is configured. In the case of FileAppender 13, you have the option of configuring it either way. See
the methods getBufferedIO() 14 and setBufferedIO(boolean) 15.
For maximum performance, you should use buffered I/O. Only switch to unbuffered I/O when you
suspect logged information may be getting lost. By default, the file appender is buffered.
7.5.6. Performance Considerations
For maximum performance, follow these rules:
1. Turn off all unnecessary logging. Set the threshold to error, fatal, or off to minimize the
amount of logging produced.
2. As has been pointed out in Section 7.5.5 Beware of Buffered Streams, make sure you are using
buffered I/O for logging.
3. If logging statements appear in a performance-critical section of code, they should be wrapped
inside an if statement that checks the current level of the logger. The &quot;\&quot; character has been
inserted where the lines were artificially broken for printing purposes:
if ( s_log.isDebugEnbled() ) {
Object expensiveMsg = &quot;parameter foo &quot; + foo + &quot; expected by the \
object &quot; +
frob + &quot; was not supplied. Oh, and the value of baz was &quot; + \
baz);
s_log.debug(expensiveMsg);
}
By making the above logging call conditional, we avoid the high cost of constructing the ex-
pensiveMsg object, if the logging level is to stricter than debug.
13. http://jakarta.apache.org/log4j/docs/api/org/apache/log4j/FileAppender.html
14. http://jakarta.apache.org/log4j/docs/api/org/apache/log4j/FileAppender.html#getBufferedIO()
15. http://jakarta.apache.org/log4j/docs/api/org/apache/log4j/FileAppender.html#setBufferedIO(boolean)
Chapter 8.
WAF Application Development Tutorial
This tutorial introduces the concepts and techniques needed to create your own application in the Red
Hat Web Application Framework. It describes how to define the application so that it can be packaged
and installed wherever the WAF platform is installed.
8.1. Terms and Assumptions
In addition to the the assumptions in Section 1 Assumptions About WAF Developers (e.g. that you have
a working understanding of object-oriented programming in Java, the Servlet API, relational schema
design, XSLT, and CSS), you should understand the WAF kernel API.
Application
A bundle of data and UI logic that is reachable via the web. Refer to Chapter 6 WAF Component:
Web.
Servlet
Code to handle a web request using the J2EE Servlet API. Throughout this document, we
assume you are familiar with version 2.3 or later of the Servlet specification. Refer to
http://jcp.org/aboutJava/communityprocess/first/jsr053/index.html.
Webapp
A web application package designed for deployment in a servlet container. A webapp instance
corresponds to a ServletContext. A WAF webapp will typically contain one Application.
PDL
The Persistence Definition Language, used to define object types in the WAF persistence layer.
Refer to Chapter 2 WAF Component: Persistence and Appendix D PDL Syntax.
8.2. Good Practices
One goal of this tutorial is to help you design an application that:
•
Uses sound patterns when integrating with WAF services.
•
Can be packaged and installed cleanly in environments other than your own.
One important consideration in developing your own application is namespace. It’s important to
pick a well-qualified name for the domain of your application and then to use this qualifier uniformly throughout your code. For the sample application we develop in this guide, we always use the
com.example.binder namespace for our PDL, Java, and other resource files.
There will be comments along the way telling you how to avoid pitfalls and where to take extra care.
8.3. Directories in the Work Area
When your webapp is complete, the packaging of the source and distribution archive depends on a
canonical layout of directories and files. This section discusses where to put them in order to create
portable, standard packages.
50
Chapter 8. WAF Application Development Tutorial
The standard layout of files in the build environment of a WAF application follows the guidelines
set out in the Tomcat Application Developer’s Guide (http://jakarta.apache.org/tomcat/tomcat-4.1doc/appdev/index.html), which are based on the Servlet specification.
binder/
The name of the directory you choose to hold your application source and build files. Our example application is a note binder, so we call our directory binder.
binder/pdl/
The PDL code for this application. As is common with Java code, it is organized into packages.
binder/pdl/com/example/binder/Binder.pdl
binder/pdl/com/example/binder/Note.pdl
binder/sql/
Custom SQL for your application. Ordinarily developers will autogenerate their SQL from PDL,
but if a custom schema is required, SQL files may be placed here to override automatic SQL
generation. See Chapter 9 Persistence Tutorial for more information. Files in this directory are
organized by relational database.
binder/src/
The source code and resources of your application reside here. As with library code, the source
is organized in packages. For example:
binder/src/com/example/binder/Binder.java
binder/src/com/example/binder/Note.java
binder/src/com/example/binder/NoteCollection.java
binder/src/com/example/binder/BinderServlet.java
binder/web/
The place for files that will become part of your webapp’s document root, such as JSPs, images,
and XSL templates. Once deployed, these files will be directly addressable via HTTP.
binder/web/logo.png
binder/web/note.jsp
binder/web/WEB-INF/
These are other resources such as compiled Java classes, property files, and resource bundles that
are used internally by your application code. Such files are not addressable.
binder/web/WEB-INF/classes
binder/web/WEB-INF/lib
Classes and jars that your application code uses go in classes/ and lib/, respectively. When
you compile and produce your webapp, these jars and classes will go with it.
8.4. Build Tools
If you choose to use the WAF build tools, you will start out with commands to build and deploy your
webapp from these directories. You can also use your own tools as long as you use this basic file layout
and follow the guidelines set out in the Jakarta webapp developer’s document specified in Section 8.3
Directories in the Work Area.
Chapter 8. WAF Application Development Tutorial
51
8.5. Modeling Your Application
A new application is represented by a persistent Application object. A typical application uses the
WAF persistence layer to store and query the state of an Application data object. An Application is more than just storage, however. It is also a set of behaviors, principally having to do with
containment and dispatch. Refer to Section 6.1 Applications to learn more.
You will subclass Application in order to introduce your own persistent properties and your own
application-specific behaviors. The data aspect of an Application is described using PDL.
This tutorial will use a sample application called Binder to illustrate how an Application is defined.
8.6. Persistent Object Types
A persistent object type definition is metadata that maps a Java object to storage in a relational schema.
As with many things in WAF, Application is one of these object types. As is the pattern for any
new application, our example creates a subtype of the Application type and adds properties to it.
model com.example.binder;
import com.arsdigita.web.Application;
// A Binder is an application that has a collection of Notes.
//
// @author Justin Ross
object type Binder extends Application {
component Note[0..n] notes = join binders.binder_id to notes.binder_id;
reference key (binders.binder_id);
}
Example 8-1. binder/pdl/com/example/binder/Binder.pdl
This definition adds just one property to Application, notes. The notes property tracks the set of
Notes belonging to a Binder.
model com.example.binder;
// A Note has a title and and body and is a component of a Binder.
//
// @author Justin Ross
versioned object type Note {
BigInteger[1..1] id = notes.note_id INTEGER;
String[1..1] title = notes.title VARCHAR(200);
String[0..1] body = notes.body VARCHAR(4000);
object key (id);
}
Example 8-2. binder/pdl/com/example/binder/Note.pdl
Observe that the Note object type is marked versioned. This means that any changes to Note will
be recorded in a change log. The WAF versioning service allows you to resurrect a specific version and
to list the changes made between two versions. For more information, refer to Section 4.11 Versioning
Service.
Once you’ve defined your PDL, the build system will generate relational tables to back your object
types.
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Chapter 8. WAF Application Development Tutorial
8.7. Java Domain Objects
Each object type will have a corresponding domain class written in Java. The domain class exists
to provide a Java-native API to your object type’s data and to behaviors that are specific to your
application. Refer to Chapter 2 WAF Component: Persistence.
package com.example.binder;
import
import
import
import
import
com.arsdigita.persistence.DataCollection;
com.arsdigita.persistence.DataObject;
com.arsdigita.util.Assert;
com.arsdigita.web.Application;
org.apache.log4j.Logger;
/**
* A collection of &lt;code&gt;Note&lt;/code&gt;s.
*
* @see com.example.binder.Note
* @author Justin Ross
*/
public class Binder extends Application {
private static final Logger s_log = Logger.getLogger(Binder.class);
public static final String BASE_DATA_OBJECT_TYPE =
&quot;com.example.binder.Binder&quot;;
static final String NOTES = &quot;notes&quot;;
protected String getBaseDataObjectType() {
return BASE_DATA_OBJECT_TYPE;
}
protected Binder(final DataObject data) {
super(data);
}
/**
* Returns all the Notes associated with this Binder.
*
* @return A &lt;code&gt;NoteCollection&lt;/code&gt; of Note objects
*/
public final NoteCollection getNotes() {
return new NoteCollection((DataCollection) get(NOTES));
}
/**
* Adds &lt;code&gt;note&lt;/code&gt; to the set of notes tracked by this
* &lt;code&gt;Binder&lt;/code&gt;.
*
* @param note The &lt;code&gt;Note&lt;/code&gt; to remove
*/
public void addNote(final Note note) {
Assert.exists(note, Note.class);
if (s_log.isDebugEnabled()) {
s_log.debug(&quot;Adding note &quot; + note + &quot; to &quot; + this);
}
add(NOTES, note);
}
Chapter 8. WAF Application Development Tutorial
53
/**
* Removes &lt;code&gt;note&lt;/code&gt; from the set of notes tracked by this
* &lt;code&gt;Binder&lt;/code&gt;.
*
* @param note The &lt;code&gt;Note&lt;/code&gt; to remove
*/
public void removeNote(final Note note) {
Assert.exists(note, Note.class);
if (s_log.isDebugEnabled()) {
s_log.debug(&quot;Removing note &quot; + note + &quot; from &quot; + this);
}
remove(NOTES, note);
}
public final String getContextPath() {
return &quot;/binder&quot;;
}
}
Example 8-3. binder/src/com/example/binder/Binder.java
The BASE_DATA_OBJECT_TYPE string specifies what PDL-defined object type this domain object
corresponds to.
The getBaseDataObjectType() method makes the runtime data object type of Binder accessible
to WAF persistence.
The DataObject constructor is a bit of plumbing necessary to make your DomainObject work, since
a DomainObject wraps a DataObject.
Everything else on Binder is there merely to expose the properties of the Binder object type as defined
in the PDL above. Binder’s UI will use the API defined here to fetch data from and to alter Binder
objects.
Note
Binder.java uses string constants that correspond to PDL-defined properties. This way the Java
compiler will catch any typos where the property is used, and a change to the PDL-defined property
name requires changing the Java code in just one place.
It’s a good idea for any WAF application to use logging to monitor important events in the lifecycles
of its objects. In the above example, any time a note is added or removed, we log what happened.
If down the line a bug appears and it’s unclear whether notes are getting added to the binder, the
developer debugging the code can simply enable correct logging and refer to whether addNote is
getting called. For more information about logging in WAF, refer to Section 7.5 Using logging for
debugging.
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Chapter 8. WAF Application Development Tutorial
package com.example.binder;
import
import
import
import
import
import
import
import
import
import
com.arsdigita.db.Sequences;
com.arsdigita.domain.DomainObject;
com.arsdigita.persistence.DataObject;
com.arsdigita.util.Assert;
com.arsdigita.util.UncheckedWrapperException;
java.io.IOException;
java.io.Writer;
java.sql.SQLException;
java.math.BigInteger;
org.apache.log4j.Logger;
/**
* A bit of text with a title.
*
* @see com.example.binder.Note
* @author Justin Ross
*/
public class Note extends DomainObject {
private static final Logger s_log = Logger.getLogger(Note.class);
public static final String BASE_DATA_OBJECT_TYPE =
&quot;com.example.binder.Note&quot;;
static final String ID = &quot;id&quot;;
static final String TITLE = &quot;title&quot;;
static final String BODY = &quot;body&quot;;
protected String getBaseDataObjectType() {
return BASE_DATA_OBJECT_TYPE;
}
protected Note(final DataObject data) {
super(data);
if (isNew()) {
try {
set(ID, Sequences.getNextValue().toBigInteger());
} catch (SQLException sqle) {
throw new UncheckedWrapperException(sqle);
}
}
}
/**
* Gets the note’s unique ID.
*
* @return The &lt;code&gt;BigInteger&lt;/code&gt; ID; it cannot be null
*/
public final BigInteger getID() {
return (BigInteger) get(ID);
}
/**
* Gets the title of the note.
*
* @return The &lt;code&gt;String&lt;/code&gt; title; it cannot be null
*/
public final String getTitle() {
return (String) get(TITLE);
}
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55
/**
* Sets the title of the note.
*
* @param title The &lt;code&gt;String&lt;/code&gt; title; it cannot be null
*/
public final void setTitle(final String title) {
if (s_log.isDebugEnabled()) {
s_log.debug(&quot;Setting title of &quot; + this + &quot; to &quot; + title);
}
Assert.exists(title, String.class);
set(TITLE, title);
}
/**
* Gets the body of the note.
*
* @return The &lt;code&gt;String&lt;/code&gt; body; it may be null
*/
public final String getBody() {
return (String) get(BODY);
}
/**
* Sets the body of the note.
*
* @param body The &lt;code&gt;String&lt;/code&gt; body; it may be null
*/
public final void setBody(final String body) {
if (s_log.isDebugEnabled()) {
s_log.debug(&quot;Setting body of &quot; + this + &quot; to &quot; + body);
}
if (Assert.isEnabled() &amp;&amp; body != null) {
Assert.truth(body.length() &lt;= 4000, &quot;The body text is too long&quot;);
}
set(BODY, body);
}
/**
* Writes an XML representation of the note and its content.
*
* @param out A &lt;code&gt;Writer&lt;/code&gt; to write the XML to
*/
public final void render(final Writer out) throws IOException {
out.write(&quot;&lt;note id=\&quot;&quot; + getID() + &quot;\&quot;&gt;&quot;);
out.write(&quot;&lt;title&gt;&quot; + getTitle() + &quot;&lt;/title&gt;&quot;);
final String body = getBody();
if (body != null) {
out.write(&quot;&lt;body&gt;&quot; + getBody() + &quot;&lt;/body&gt;&quot;);
}
out.write(&quot;&lt;/note&gt;&quot;);
}
}
Example 8-4. binder/src/com/example/binder/Note.java
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Chapter 8. WAF Application Development Tutorial
In many ways, Note.java is just like Binder.java. It declares its data object type; it defines an
instantiator; and it adds some plumbing for getting the runtime data object type and for constructing
a wrapper DomainObject.
Since the properties of the data object type differ from those of Binder, the Java accessors and mutators
are different. Of more interest is the fact that Note has additional business logic for outputting the
Note object as XML.
Note
The setTitle method uses assertions to enforce the contract set out in the object-type definition.
The title property is marked [1..1] in Note.pdl, so it cannot have a null value. Therefore, we
assert that calling setTitle(null) is a failure condition.
Note
If your code includes assertions that do work in their arguments, make sure to wrap the assertion
code in an if statement that checks that assertions are turned on:
if (Assert.isEnabled() &amp;&amp; body != null) {
Assert.truth(body.length() &lt;= 4000, &quot;The body text is too long&quot;);
}
Example 8-5. Using assertions
Be careful, however, that this is what you really want. Assertions exist to detect unexpected, unrecoverable program failures. Don’t use them for other types of errors, such as user input validation, since
they can be disabled.
The WAF persistence API gives us efficient cursor-oriented access to the elements of an association.
The NoteCollection object gives our UI code access to the data for each row returned from a query
for multiple Notes.
package com.example.binder;
import com.arsdigita.domain.DomainCollection;
import com.arsdigita.persistence.DataCollection;
import org.apache.log4j.Logger;
/**
* Represents a collection of {@link com.example.binder.Note notes}.
*
* @author Justin Ross
*/
public class NoteCollection extends DomainCollection {
private static final Logger s_log = Logger.getLogger(NoteCollection.class);
public NoteCollection(final DataCollection data) {
super(data);
}
/**
* Gets the title of the current note.
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57
*
* @return The &lt;code&gt;String&lt;/code&gt; title; it cannot be null
*/
public final String getTitle() {
return (String) get(Note.TITLE);
}
/**
* Gets the body of the current note.
*
* @return The &lt;code&gt;String&lt;/code&gt; body; it may be null
*/
public final String getBody() {
return (String) get(Note.BODY);
}
}
Example 8-6. binder/src/com/example/binder/NoteCollection.java
8.8. Initializing the Application Runtime Environment
To get your application up and running, there are some things you need to do every time the WAF
runtime starts up. Initializers exist to help you execute such code.
package com.example.binder;
import
import
import
import
import
import
import
import
import
import
import
com.arsdigita.db.DbHelper;
com.arsdigita.domain.DomainObject;
com.arsdigita.domain.DomainObjectInstantiator;
com.arsdigita.persistence.DataObject;
com.arsdigita.persistence.pdl.ManifestSource;
com.arsdigita.persistence.pdl.NameFilter;
com.arsdigita.runtime.CompoundInitializer;
com.arsdigita.runtime.DomainInitEvent;
com.arsdigita.runtime.PDLInitializer;
com.arsdigita.runtime.RuntimeConfig;
org.apache.log4j.Logger;
/**
* Initializes the binder application.
*
* @see com.example.binder
* @author Justin Ross
*/
public class Initializer extends CompoundInitializer {
private static final Logger s_log = Logger.getLogger(Initializer.class);
public Initializer() {
final String url = RuntimeConfig.getConfig().getJDBCURL();
final int database = DbHelper.getDatabaseFromURL(url);
add(new PDLInitializer
(new ManifestSource
(&quot;binder.pdl.mf&quot;,
new NameFilter(DbHelper.getDatabaseSuffix(database), &quot;pdl&quot;))));
}
public void init(final DomainInitEvent e) {
super.init(e);
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e.getFactory().registerInstantiator
(Binder.BASE_DATA_OBJECT_TYPE,
new DomainObjectInstantiator() {
protected final DomainObject doNewInstance
(final DataObject data) {
return new Binder(data);
}
});
}
}
Example 8-7. binder/src/com/example/binder/Initializer
In the section above, you defined object-relational mapping metadata. The PDLInitializer serves
to load that metadata into the runtime. This allows the persistence layer to interpret requests for the
data behind your persistent object types.
The Binder and Note persistent object types have corresponding domain classes written in Java. The
domain APIs will return the Java objects, but to do so we must map the object type to something that
can instantiate the Java class.
public void init(final DomainInitEvent e) {
super.init(e);
e.getFactory().registerInstantiator
(Binder.BASE_DATA_OBJECT_TYPE,
new DomainObjectInstantiator() {
protected final DomainObject doNewInstance
(final DataObject data) {
return new Binder(data);
}
});
}
Example 8-8. Coupling data objects to domain object instantiators
When your package is loaded, the package tool will store the initializer class name you provide in the
database. When the CCM runtime starts up, it will read out all the registered initializers and run them
in order to prepare the environment.
8.9. Creating a Web Interface
WAF uses the Servlet API for handling web requests. Any standard servlet, adapted to use the WAF
servlet facilities (com.arsdigita.web.BaseApplicationServlet and related classes), can be
used to serve your content. For our example application, we will use a basic Servlet to create our
UI . For information on how to create a UI for your application using Bebop, refer to Chapter 12
Presentation (Bebop) Tutorial.
package com.example.binder;
import
import
import
import
import
import
import
com.arsdigita.web.Application;
com.arsdigita.web.BaseApplicationServlet;
java.io.IOException;
javax.servlet.ServletException;
javax.servlet.http.HttpServletRequest;
javax.servlet.http.HttpServletResponse;
org.apache.log4j.Logger;
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59
/**
* A servlet to serve pages of the binder application.
*
* @see com.example.binder.Binder
* @author Justin Ross
*/
public final class BinderServlet extends BaseApplicationServlet {
private static final Logger s_log = Logger.getLogger(BinderServlet.class);
public void doService(final HttpServletRequest sreq,
final HttpServletResponse sresp,
final Application app)
throws ServletException, IOException {
sresp.getWriter().write(&quot;YO&quot;);
}
}
Example 8-9. binder/src/com/example/binder/BinderServlet.java
An Application is associated with a path into the servlet container. The WAF dispatcher will look up
your application and use its getContextPath and getServletPath methods to dispatch to your
UI code. Our webapp will be mounted as binder in the servlet container, so we specify Binder’s
context path to be /binder.
public final String getContextPath() {
return &quot;/binder&quot;;
}
Example 8-10. Setting the application’s dispatch destination
When the dispatcher encounters a request for an instance of the binder application, it will look up the
appropriate Binder object and use its getContextPath and getServletPath methods to dispatch
to the appropriate servlet code, in this case BinderServlet.
By specifying the servlet path this way, we index into the servlet container’s native method of dispatch,
by pattern. Your servlet container uses a webapp-standard file web.xml to declare pattern-to-servlet
mappings.
&lt;!DOCTYPE web-app
PUBLIC &quot;-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN&quot;
&quot;http://java.sun.com/j2ee/dtds/web-app_2_3.dtd&quot;&gt;
&lt;web-app&gt;
&lt;servlet&gt;
&lt;servlet-name&gt;binder&lt;/servlet-name&gt;
&lt;servlet-class&gt;com.example.binder.BinderServlet&lt;/servlet-class&gt;
&lt;/servlet&gt;
&lt;servlet-mapping&gt;
&lt;servlet-name&gt;binder&lt;/servlet-name&gt;
&lt;url-pattern&gt;/*&lt;/url-pattern&gt;
&lt;/servlet-mapping&gt;
&lt;/web-app&gt;
Example 8-11. binder/web/WEB-INF/web.xml
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8.10. Integrating Your Package With CCM Tools
The WAF environment includes a set of tools for loading and configuring software such as our example
application. In order to integrate with those tools, your application needs to supply some information
in the right places.
The CCM package loader, part of the ccm command line tool, takes a package and loads its initial
configuration, schema, and data. ccm is documented in the Red Hat Web Application Framework
Installation Guide.
$ ccm load --interactive binder
This command will ultimately run a Loader, a class that loads a package’s schema and data. So that
the CCM tool can invoke the correct loader, a file of the form ${package-key}.load is required
directly under your application’s src/ directory.
&lt;?xml version=&quot;1.0&quot; encoding=&quot;utf-8&quot;?&gt;
&lt;load&gt;
&lt;provides&gt;
&lt;table name=&quot;binders&quot;/&gt;
&lt;table name=&quot;notes&quot;/&gt;
&lt;initializer class=&quot;com.example.binder.Initializer&quot;/&gt;
&lt;/provides&gt;
&lt;scripts&gt;
&lt;schema directory=&quot;binder&quot;/&gt;
&lt;data class=&quot;com.example.binder.Loader&quot;/&gt;
&lt;/scripts&gt;
&lt;/load&gt;
Example 8-12. binder/src/binder.load
The table names in the provides block will be checked to ensure they exist when the package
tool prepares to load the binder package. The initializer classname dictates what initializer will be run
when the CCM runtime starts up. The schema directory given in the scripts block tells the base
Loader implementation where to find the schema it will load. The optional data class allows you to
use a Loader implementation specific to your package.
8.11. Creating Upgrade Scripts
Upgrading to new versions of WAF applications may require you to also migrate your data. WAF
supports two complementary approaches to data migration: Java upgrade programs and SQL scripts.
Java upgrade programs have full access to the WAF and application APIs. These programs are typically used to do more complex migrations where executing business logic is required to correctly
migrate existing data.
SQL upgrade scripts rely on SQL and the embedded database procedural language (e.g., PL/SQL)
to migrate data. SQL scripts are typically used to change database schemas. They also may provide
superior performance in migrating large amounts of data.
The purpose of this section is to assist you in creating and hooking up your Java upgrade script
to take advantage of WAF APIs. The process for performing the actual application upgrade from
the installation/administration side using the ccm upgrade tool is covered in the WAF Installation
Guide.
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61
Creating A ccm Tool Upgrade Script in Java
1. Create arbitrary Java code that is accessible via a static main() method.
## file called com/arsdigita/cms/AnUpgrade.java
package com.arsdigita.cms;
public class AnUpgrade {
public static void main(String[] args) {
System.out.println(&quot;Sample upgrade running&quot;);
}
}
2. Create or edit the upgrade spec file at ${package_name}.upgrade on the classpath. The file
described looks like this:
## file called ccm-cms.upgrade
&lt;upgrade&gt;
&lt;version from=&quot;6.0&quot; to=&quot;6.1&quot;&gt;
&lt;script class=&quot;com.arsdigita.cms.RickshawPublishAPIUpgrade&quot;/&gt;
&lt;/version&gt;
&lt;version from=&quot;6.0&quot; to=&quot;7.0&quot;&gt;
&lt;script class=&quot;com.arsdigita.cms.AnUpgrade&quot;/&gt;
&lt;script sql=&quot;ccm-cms/upgrade/::database::-6.0-7.0.sql&quot;/&gt;
&lt;/version&gt;
&lt;/upgrade&gt;
Creating a SQL Upgrade Script
1. Create arbitrary SQL code to update the schema or data, and place the code in a file with the
.sql suffix. Group all related functional changes in a single file and assign the file a descriptive
functional name e.g., update-host-unique-index.sql.
2. Update the appropriate parent upgrade script to reference the created SQL script. Parent scripts are
stored in sql/ccm-core/upgrade. Each database has its own set of versioned upgrade scripts,
e.g., oracle-se-6.0.1-6.1.0.sql.
For Java upgrade scripts, the class for the given version-version pair will be invoked (via its
main() method) when the user runs, e.g., ccm upgrade ccm-cms --from-version 6.0
--to-version 7.0. For SQL scripts, the given SQL file will be loaded as a resource from the
classpath and run. The &quot;::database::&quot; placeholder will be substituted with a short string identifying
the current database, oracle-se or postgres, before the resource is loaded.
Note
Only exact matches on both the from and the to versions will trigger script execution.
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Chapter 9.
Persistence Tutorial
This chapter presents a tutorial for using the persistence system. It presumes you are familiar with the
concepts covered in Chapter 2 WAF Component: Persistence.
This tutorial will first discuss using Data Objects, which is followed by a tutorial on using the features
of PDL. Referenced throughout this tutorial is the Persistence Glossary.
9.1. Data Objects Tutorial
This section has been assembled to help familiarize you with the concepts and functionality of the
persistence layer. This section assumes a familiarity with the concepts discussed in Chapter 2 WAF
Component: Persistence and in Persistence Glossary. It also assumes that the code is being executed
within a standard WAF installation.
This tutorial will walk you through the use of object persistence in the WAF. It begins by showing you
how to ensure that your server is set up correctly so that the PDL will compile. It then continues with
a simple example of how to create a PDL file and how to write the corresponding Java code to interact
with the database.
After covering the basics of using standalone Data Objects, the tutorial describes how to associate
objects to each other. It discusses several examples, including how to retrieve Data Objects through
arbitrary queries. The tutorial concludes with a list of common mistakes that are made by developers.
9.2. Beginning With Data Objects
This section starts with the basic steps that are required to access information in the database using the
persistence layer. It begins by discussing PDL and Data Objects. It then discusses how to create the
database schema and how it can be represented in PDL. Finally, it covers using the properties defined
in the PDL to access the database in your Java code.
9.2.1. Data Objects and PDL: How are they related?
The persistence layer can be looked at as a way to access objects within the database. Examples of
objects that can be stored in the database are Users, Groups, Articles, Images, and Email Addresses.
In order to abstract out the information regarding object storage within the database, the persistence
layer has implemented the concept of a single Data Object. Data Objects are used by Java classes
to handle all interaction with the database. Because this class is provided, other classes do not need
to know how to create, retrieve, update, or delete a given object. Data Objects are defined by their
Attributes and Object Key.
Every Data Object is associated with a single Object Type. Every object type, in turn, is associated
with events and operations that specify how information is stored in the database and how information
in the database is mapped to Java variables. The role of the PDL file (see Section 9.2.3.1 The PDL
File) is to provide developers with a mechanism to easily specify that object type.
9.2.2. Setting up the Schema
When defining your persistence layer, you need to work through two aspects of your design:
•
A UML model of your Data Objects.
64
•
Chapter 9. Persistence Tutorial
A database schema to handle the storage of the Data Objects.
Some designers may feel more comfortable starting with a database design and then designing the
objects that use the schema, or vice versa. You may begin with either one, but both should be designed
as part of the persistence layer. The UML model is typically designed for the Data Objects using a
UML modeling tool.
This tutorial will use a hypothetical database schema composed of publications, magazines, articles,
paragraphs, and authors. This goal of this tutorial is to help you better understand how this technology
can be used with WAF. In practice, the entire data model below will be automatically generated by the
persistence layer using the metadata defined in the PDL file. Therefore, none of the data model below
will have to be created by the developer.
The tutorial will begin by using two simple objects: a Publication and a Magazine. The schema will
be expanded throughout the tutorial. To see the full schema that is used throughout the tutorial, please
see Appendix D PDL Syntax.
create table publications (
publication_id
integer
constraint publications_pub_id_nn
not null
constraint publications_pub_id_pk
primary key,
type
varchar(400)
constraint publications_pub_type_nn
not null,
name
varchar(400)
constraint publications_pub_name_nn
not null,
constraint publications_pub_name_un unique(type, name)
);
create table magazines (
magazine_id
integer
constraint magazines_magazine_id_fk
references publications
constraint magazines_magazine_id_pk
primary key,
issue_number
varchar(30)
);
9.2.3. Defining an Object Type in PDL
9.2.3.1. The PDL File
A PDL file is a text file that has a .pdl extension and can be parsed using the PDL grammar (Appendix
D PDL Syntax). It is made up of a model declaration followed by block declarations. These block
declarations can be object type definitions, association blocks, Dara Query blocks, and Data Operation
blocks.
The only required item is the Model declaration, as this declaration informs the compiler of which
namespace to use. It is common to have one for all DataQuery and DataOperation definitions and
one file for each Object Type. However, it is possible to combine all Object Type definitions into a
single file. It is also possible to include DataQuery and DataOperations in their own files or inline with Object Type Definitions. Data Associations are normally found with one of the Object Type
definitions used within the association.
You can find a list of PDL reserved words, as well as the PDL grammar, in Appendix D PDL Syntax.
Chapter 9. Persistence Tutorial
65
9.2.3.2. Model and Object Type
When creating a PDL file, the first line of the file must be the name of the model that defines the
namespace for the block definitions in the PDL file. This is similar to the name of the package in
a Java class and is necessary to avoid name collisions of object types that have the same name and
which exist in different PDL files. This example will use the tutorial model.
The second block of lines within a PDL file can either be a list of namespaces to import (similar to
Java’s import statement) or the declaration of the object type itself. See Section 9.2.6 Object Type
Inheritance for more information about importing.
The object type definition follows the import statement. The definition of an object type may include
attributes and event definitions. The Publication object type defined below has two attributes defined.
One of these attributes, id, is also part of the object key, which means that a Publication is uniquely
identified by the id attribute value.
The first block of code within the object type definition is a list of persistence attributes and mappings
of those attributes to database columns for the given object. Note that the attribute names do not need
to be the same as the column names. The attributes are a list of Java variables that a given Data Object
class can access. Finally, notices that in addition to the java data type at the beginning of the attribute
mapping the SQL data type is also present. This SQL data type allows for DDL generator to generate
the correct SQL. For a complete list of supported Java types, see Section D.2.2 PDL Attribute Types
// declare the namespace as &quot;tutorial&quot; using the &quot;model&quot; keyword
model tutorial;
// there are not any import statements because Publication does not
// extend anything.
// next comes the &quot;object type&quot; keyword followed by the name of
// the object type
object type Publication {
// the first block of code within the object type is a set of
// mappings from the Attribute Java type and Attribute name to
// the database column to which they correspond.
BigDecimal id = publications.publication_id INTEGER;
String name = publications.name VARCHAR(400);
}
9.2.3.3. Object Key
For each object type, you must define an object identifier for the purposes of uniquely identifying
object instances at run time. If the object type does not have a super type, the object key syntax is
used. If the object has a super type, a reference key must be declared to indicate how this object
joins with the supertype. (See Section 9.2.6 Object Type Inheritance for more details.) The following
example indicates how to designate that the Publication’s id attribute is the object identifier or key:
model tutorial;
object type Publication {
BigDecimal id = publications.publication_id INTEGER;
String name = publications.name VARCHAR(400);
String type = publications.name VARCHAR(400);
object key (id);
}
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Chapter 9. Persistence Tutorial
This object type definition almost models the SQL that we have defined above but it is missing any
mention of the unique constraint. To allow for this and to allow the DDL generator to correctly generate unique constraints the persistence layer allows you to specify either a single property or a set of
properties as being unique. The syntax for this is as follows:
SINGLE UNIQUE PROPERTY:
object type User {
BigDecimal id = users.id INTEGER;
unique String[0..1] screenName = users.screen_name VARCHAR(100);
...
}
SET OF UNIQUE PROPERTIES:
object type Node {
BigDecimal id = nodes.id INTEGER;
Node[0..1] parent = join nodes.parent_id to nodes.id;
String[1..1] name = nodes.name VARCHAR(100);
object key (id);
unique (parent, name);
}
Therefore, in order to correctly model the publications, we need to add the constraint. The correct,
full publications object type defintion is below:
model tutorial;
object type Publication {
BigDecimal id = publications.publication_id INTEGER;
String name = publications.name VARCHAR(400);
String type = publications.name VARCHAR(400);
object key (id);
unique (name, type);
}
Note
Attributes cannot have the same name as a pdl reserved word without special quoting. For a list of
reserved words and escaping techniques, see Section D.2 PDL Reserved Words.
9.2.4. Getting Started with the API
Now that we know how to specify an Object Type using PDL, you can learn how to access the information from Java. The first step is to examine the public API that is provided by the persistence
system.
The persistence layer in the Web Application Framework is implemented in the Java package
(http://rhea.redhat.com/doc/waf/6.0/api/com/arsdigita/persistence/package-summary.html).
This
package contains a set of classes and interfaces for working with persistent objects that store
themselves in a relational database. Some of the URLs listed contain a visual break with the &quot;\&quot;
character for printing formatting.
Chapter 9. Persistence Tutorial
• SessionManager
Manager.html.
67
— http://rhea.redhat.com/doc/waf/6.0/api/com/arsdigita/persistence/\ Session-
This class is responsible for initializing the Session class. Users of persistence will use
it to get a pointer to the Session class through SessionManager.getSession()
(http://rhea.redhat.com/doc/waf/6.0/api/com/arsdigita/persistence/\
SessionManager.html#getSession()).
• Session
— http://rhea.redhat.com/doc/waf/6.0/api/com/arsdigita/persistence/Session.html
All persistence operations take place within the context of a session. The Session object contains
methods for creating and retrieving data objects, data queries, and data operations.
• DataObject — http://rhea.redhat.com/doc/waf/6.0/api/com/arsdigita/persistence/DataObject.html
This interface defines the public methods for Data Objects; see Data Object.
Data Objects are normally accessed through the use of DomainObjects
(http://rhea.redhat.com/doc/waf/6.0/api/com/arsdigita/domain/DomainObject.html).
• OID
— http://rhea.redhat.com/doc/waf/6.0/api/com/arsdigita/persistence/OID.html
This class represents a unique identifier for a given Data Object. It typically holds the information in
the object key (Object Key) of the object type. For the WAF Object type, the OID is the combination
of the &quot;acs object type&quot; (e.g., com.arsdigita.User) and the &quot;object id&quot;. This is typically used to
retrieve specific objects from the database.
• DataQuery
— http://rhea.redhat.com/doc/waf/6.0/api/com/arsdigita/persistence/DataQuery.html
This class represents an interface for retrieving arbitrary information from the database. It is the
Java equivalent of the PDL data query described in Section 9.4.1 Data Queries.
• DataOperation
ation.html
— http://rhea.redhat.com/doc/waf/6.0/api/com/arsdigita/persistence/\ DataOper-
This class represents an interface for executing arbitrary DML within the database. It is the Java
equivalent of the PDL data operation described in Section 9.4.2 Data Operations.
• DataCollection
lection.html
— http://rhea.redhat.com/doc/waf/6.0/api/com/arsdigita/persistence/\ DataCol-
This class is used to represent a collection of data objects. DataCollections can be used to
efficiently iterate over a large set of DataObjects and access the values of their properties. These
can be filtered in a manner similar to DataQueries.
• DataAssociation — http://rhea.redhat.com/doc/waf/6.0/api/com/arsdigita/persistence/\
sociation.html
DataAs-
This class is similar to the Java Collection interface, in that it provides
methods that act on the entire set of associations, such as add(DataObject
object)
(http://rhea.redhat.com/doc/waf/6.0/api/com/arsdigita/persistence/\
DataAssociation.html#add(com.arsdigita.persistence.DataObject)),
and
methods
that
return
other
objects
to
access
the
associations,
such as
cursor()(http://rhea.redhat.com/doc/waf/6.0/api/com/arsdigita/persistence/\
DataAssociation.html#cursor()).
• DataAssociationCursor
DataAssociationCursor.html
— http://rhea.redhat.com/doc/waf/6.0/api/com/arsdigita/persistence/\
Like a Java Iterator, this is used to loop over a set of associations. Developers can also add Filters
to DataAssociationCursors, thereby restricting the objects returned to the desired subset.
• Filter
— http://rhea.redhat.com/doc/waf/6.0/api/com/arsdigita/persistence/Filter.html
This class is used to filter the results of associations and collections. For instance, if a developer
only wants the associated objects with a name starting with &quot;l&quot; then a filter is used.
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• PersistenceException
PersistenceException.html
— http://rhea.redhat.com/doc/waf/6.0/api/com/arsdigita/persistence/\
This is an unchecked exception that is thrown whenever there is an error within the persistence
system. It typically contains an error message as well as some debugging information.
9.2.5. Creating and Retrieving Objects in Java
Now that you have written your PDL files and your database is loaded, the next step is to create Data
Objects to access the information in the database. The main access point to Data Objects is through
the Session class. Session objects allow you to instantiate data objects that are part of a logical
client session. Specifically, there are three methods that allow you to create and retrieve objects as
well as a method allowing you to delete an object.
Suppose you have defined a Publication and want to create a new DataObject so that you can store
information about it. The first step is to use the Session.create(String typeName) method. You
can pass in the fully qualified name of the Object Type and get a Data Object back that corresponds
to the defined events. For instance, to create a new Publication, you can do the following (remove the
&quot;\&quot; and make it all one line):
DataObject publication = SessionManager.getSession().create\
(&quot;tutorial.Publication&quot;);
If you want to retrieve an object that already exists (and you have the OID), you can use the Session.retrieve(OID oid) method. This is similar to the creation method, except that you are
accessing a row that already exists in the database instead of creating a new row (or rows).
If you have an OID and you want to delete the object from the database, Session provides a
delete(OID oid) method that allows you to perform the deletion. For most cases, however, you
will have the DataObject and can just call the local delete() method.
The above methods show how to retrieve or create a single object within the system. The system also
provides the ability to retrieve all objects of a given object type. This capability is provided through
the method retrieve(String typeName), located in the Session class.
Suppose you want to print out the names of all of the Publications in the system whose ID is less than
100. One way to do this would be to loop from 1 to 100, create the corresponding OID, and look up
each Publication. Another way would be to use a Data Query. However, the simplest way is to take
advantage of the retrieve all event that is generated for the Magazine object type. The following
example demonstrates this (remove the &quot;\&quot; and make it all one line):
// get all of the Publications in the system. Calling &quot;retrieve&quot; triggers
// the &quot;retrieve all&quot; event defined in the PDL file. Note that
// the string passed in to the method is the model name (tutorial)
// followed by the object type name (Publication) separated by a dot (.).
DataCollection pub = SessionManager.getSession().retrieve\
(&quot;tutorial.Publication&quot;);
// now we want to filter on the ID of the publication
pub.addFilter(pub.getFilterFactory().addLessThan(&quot;id&quot;, new Integer(100), \
false));
// finally, we can loop through the publications and print out its name
//
// the query to get the information out of the database is executed
// when next() is called for the first time
while (pub.next()) {
System.out.println(pub.get(&quot;name&quot;));
}
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DataCollections are also useful when it is necessary to perform certain tasks on a large number
of Data Objects. Suppose you want to add the publications to a java.util.Collection that can then be
passed around. The following code will create the java.util.Collection (remove the &quot;\&quot; and make it all
one line):
DataCollection publication = SessionManager.getSession().retrieve\
(&quot;tutorial.Publication&quot;);
Collection collection = new ArrayList();
pub.addFilter(pub.getFilterFactory().addLessThan(&quot;id&quot;, new Integer(100), \
false));
while (pub.next()) {
collection.add(pub.getDataObject());
}
Note
Please note the following:
• Most creation of Data Objects should be handled through the use of Domain Objects. All ACSObjects are also DomainObjects and therefore can use the DomainObject API to retrieve the correct
information. For more information, please see the Section 10.2 Domain Objects Tutorial.
• The DataCollection class does NOT extend the java.util.Collection interface, nor does it extend
the java.util.Iterator interface.
9.2.6. Object Type Inheritance
Now that you know how to create and access information for a specific object type, the next logical
step in Object-Oriented programming is to create an object type that extends another object type. To
address this problem, PDL allows object types to inherit attributes from other object types, similar to
inheritance in most Object-Oriented programming languages.
The following example shows a &quot;Magazine&quot; object type extending the &quot;Publication&quot; object type. The
definition for the &quot;Magazine&quot; is very similar to that of &quot;Publication&quot; in that it has a block of attributes.
It is different, however, in that it does not have an object key definition. Rather, it has a reference
key which indicates how the table containing the Magazine information can be joined to the table
containing the Publication information. If the Magazine tries to define an object key, an error will
be thrown.
model tutorial.magazine;
// we do not have to import the tutorial model because both object types
// are in the same model. However, we show the import statement here as
// an example.
import tutorial.*;
object type Magazine extends Publication {
// we need to specify the size of the String attribute so we know
// whether it is actually a String or if it is really a Clob
String issueNumber = magazines.issue_number VARCHAR(30);
// notice that because it extends Publication, there is not an
// explicitly &quot;object key&quot; declaration. Rather, there is
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// a &quot;reference key&quot; declaration and &quot;id&quot; is not defined
// as one of the attributes
reference key (magazines.magazine_id);
}
9.3. Associations
So far, the documentation has discussed how to create simple Data Objects to access the database.
These features, while sufficient to build many systems, lack the ability to relate object types to each
other. To address these needs, the persistence system contains the concept of associations.
This document discusses how the persistence layer allows developers to associate Data Objects and
how these associations can be saved in the database without needing to involve the Java code in how
the associations are actually stored. More concretely, the document first discusses how an association
is structured within PDL. It then defines the PDL for Articles, Paragraphs, and Authors and
show hows to relate them through Two-Way Associations, Composite Associations, and One Way
Associations.
9.3.1. Association Blocks
Most commonly you associate objects to each other when both objects need to know to which objects
they are associated. Magazines and Articles, Users and Groups, and Employees and Offices are all
examples of this type of association. In the PDL below, an Article Object Type and an &quot;association
block&quot; are defined to associate the Articles to Magazines. Association Block definitions are similar to Object Type definitions in that they both have attribute definitions. Instead of the Attribute being
set as equal to a single column within the database, the Attribute is set as equal to a Join Path.
object type Article {
BigDecimal id = articles.title;
String title = articles.title;
object key (articles.article_id);
}
// this is an &quot;association block&quot; associating &quot;articles&quot; and &quot;magazines&quot;
association {
// note that the Attribute Type is an Object Type (Article)
// and not a standard Java Type. Also notice the order of the
// join path and see the note below.
Article[0..n] articles = join magazines.magazine_id
to magazine_article_map.magazine_id,
join magazine_article_map.article_id
to articles.article_id;
Magazine[0..n] magazines = join articles.article_id
to magazine_article_map.article_id,
join magazine_article_map.magazine_id
to magazines.magazine_id;
}
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71
Note
The order of the join path is important. The information that the developer has must come first.
That is, when the developer needs to retreive articles, the information he has is the Magazine
(he needs to know for which magazine to get the articles). Therefore, the first line of the join path
specifies how to join the magzines table to the mapping table. From then on, it should be in order so
that the last section of the join element uses the same table as the first section of the next join
element.
9.3.2. Composite Associations
Composite relationships are a special type of Association. Composite relationships are useful for modeling relationships between objects where a contained object cannot exist outside its container object.
The main difference between a Composition and a standard Association is that within a Composition,
one of the objects cannot exist without the other.
In the following example, a Paragraph is a component of the Article (they therefore have a composite relationship). That is, it does not make sense for a Paragraph to exist outside of an article. There
are many different ways to signify a relationship as composite but the easiest way is to add the component keyword before the component Object Type (in this case, the paragraph is a component of
the article)
object type Paragraph {
BigDecimal id = paragraphs.paragraph_id INTEGER;
String text = paragraphs.text VARCHAR(4000);
object key (paragraphs.paragraph_id);
}
association {
Article[1..1] articles = join paragraphs.article_id
to articles.article_id;
// notice the component keyword indicates that if the article does
// not exist then the paragraph also does not exist
component Paragraph[0..n] paragraphs = join articles.article_id
to paragraphs.article_id;
}
Another way to make the same association is to use the composite keyword on the role that points
toward the composite end of an association in order to indicate that the association is a composition.
For example:
association {
composite Article[1..1] articles = join paragraphs.article_id
to articles.article_id;
Paragraph[0..n] paragraphs = join articles.article_id
to paragraphs.article_id;
}
The final way to signify the relationship is to use keywords for both object types. This displays the
same behavior as the two examples above but it also valid.
association {
composite Article[1..1] articles = join paragraphs.article_id
to articles.article_id;
component Paragraph[0..n] paragraphs = join articles.article_id
to paragraphs.article_id;
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}
9.3.3. Role References
Developers ofen only need to be able to obtain associated information in a single direction. For instance, if authors have screen names that are used and can be shared, it is useful to be able to look
up the screen name for a given author. However, it may not be as important to look up the author
that corresponds to a given screen name. In this case, developers should use a Role Reference. In the
following example, the developer wants to be able to easily look up a given screen name for an author.
The PDL below can be used to create Object Types for both ScreenName and Author. Notice that
Author contains a role reference to a ScreenName.
model tutorial;
object type ScreenName {
BigDecimal id = screen_names.name_id INTEGER;
String screenName = screen_names.screen_name VARCHAR(200);
Blob screenIcon = screen_names.screen_icon BLOB;
object key (id);
}
object type Author {
BigInteger[1..1] id = authors.author_id INTEGER;
String[1..1] firstName = author.first_name VARCHAR(700);
String[1..1] lastName = author.last_name VARCHAR(700);
Blob[0..1] portrait = authors.portrait BLOB;
// the following line is the role reference. Notice that it
// appears in the definition just like an Attribute. The only
// difference is that instead of pointing to a column in the
ScreenName[0..1] screenName =
join authors.screen_name_id to screen_names.name_id;
object key (id);
}
9.3.4. Link Attributes
One final feature that is immensely useful for associating objects is the idea of Link Attributes. Often,
some sort of relationship is needed for associations. For instance, for Magazines, it is useful to include
the page number with the Article. The concept of having Articles associated with Magazines is
covered by standard associations but in order to capture a page number with the association, Link
Attributes are needed.
// this is an &quot;association block&quot; associating &quot;articles&quot; and &quot;magazines&quot;
association {
Article[0..n] articles = join magazines.magazine_id
to magazine_article_map.magazine_id,
join magazine_article_map.article_id
to articles.article_id;
Magazine[0..n] magazines = join articles.article_id
to magazine_article_map.article_id,
join magazine_article_map.magazine_id
to magazines.magazine_id;
// the next line is the Link Attribute. Note that it also specifies
// the SQL type of INTEGER so that the DDL generator can correctly
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// create the mapping table with the page_number column.
BigDecimal pageNumber = magazine_article_map.page_number INTEGER;
}
For more information about Link Attributes and their use, see Section 9.8 Link Attributes.
9.3.5. Using Java to Access Associations
Now that you have seen how to declare associations within PDL, you can learn the different ways to
access the information from Java. In Java, Associations are accessed with two classes: DataAssociation, similar to a Java Collection, and DataAssociationCursor, similar to a Java Iterator.
9.3.5.1. Using Standard Associations
public Collection getArticles(DataObject obj) {
LinkedList articles = new LinkedList();
DataAssociationCursor cursor =
((DataAssociation) obj.get(&quot;articles&quot;)).cursor();
while (cursor.next()) {
articles.add(cursor.getDataObject());
}
return articles;
}
The next example shows how to associate one item with another. In this case, you are associating an
Article with a Magazine by adding the article to the &quot;articles&quot; association. By calling save(), you
are signalling for the data object to fire the appropriate insert and update association events (remove
the &quot;\&quot; and make it all one line).
public void addArticle(DataObject magazine, DataObject article) {
DataAssociation association = (DataAssociation) magazine.get\
(&quot;articles&quot;);
association.add(article);
magazine.save();
}
Note
There are two important things to realize when dealing with adding items to Associations and
iterating through them:
• Unlike DataCollection, DataAssociation has been separated into two distinct entities. If you
want to loop through the items in the association, or filter or order the association, use a DataAssociationCursor. If you want to add or remove items from the association, use the DataAssociation object. The DataAssociation is a property of the DataObject and is shared by all code
accessing the data object. The DataAssociationCursor is essentially a local copy of the associ-
ation that can be filtered, ordered, and iteratred through without any external consequences.
• While this next item is actually a feature of Domain Objects, it is important to mention here as
well. When adding items to associations using the DomainObject (and therefore any ACSObject),
there are three choices of which method to use. If the association has an association of 0..n
(or any upper bound
1), developers should use the add(String propertyName, DataObject
dataObject) method or the add(String propertyName, DomainObject dobj) method. If the
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association has a Multiplicity of 0..1 or 1..1 (or any upper bound = 1) then developers should use
the setAssociation(String attr, DomainObject dobj) method.
9.3.5.2. Using Role References
Role References can be treated in exactly the same way as standard associations. The only practical
difference between Role References and standard associations is that Role References are one-way
associations and standard associations are two-way associations. Thus, everything outlined in Section
9.3.5 Using Java to Access Associations also applies to Role References.
9.3.5.3. Using Copmposite Associations
Composite Associations are also similar to standard associations. The main difference is that in a
composite association, if one item is deleted, the other does not have any real meaning (e.g., if you
delete an Article, the Paragraph is meaningless).
Again, these can be accessed exactly as associations except for one significant difference: when the
association between an object and its component is deleted, the component is also deleted. For example, if the association between an Article and a Paragraph were deleted, the Paragraph would be
deleted. Also, when the Article is deleted, the Paragraph is deleted.
9.4. Named SQL Events
So far, we have outlined how to interact with the database in a controlled, structured fashion. While
creating standard data objects and associations handles most developing needs, sometimes a developer
needs to perform database queries that do not fit within the standard realm of objects and associations.
It is also often the case that developers are able to perform operations in a single operation that would
normally take the system multiple operations. This situation has been handled in two separate ways
through the introduction of Data Queries (for selects) and Data Operations (for DML).
9.4.1. Data Queries
Developers often come across situations in which they need information from the database and the
persistence layer does not quite do what is needed. Therefore, the system has the ability to execute
arbitrary queries through the use of a DataQuery.
9.4.1.1. Retrieving Information from the Database
Executing arbitrary queries through DataQueries is easy. You can retrieve them in the same way
that you retrieve an existing data object, and you can execute the query and loop through the results
in the same way that you use a DataAssociationCursor.
To begin, you retrieve a query through the Session object using its model and name. Then, you can
use next() to loop through the results.
For example, if you want all paragraphs that show up in the magazine with issue number 5A. The first
step is to define the query within the PDL file. A DataQuery definition has four sections. It begins
with the declaration of the name of the query followed by data type mappings for each returned
attribute. It concludes with two code blocks. The first block, the DO block, contains the actual SQL
that will be executed. The second block, the MAP block, allows the developer to map database columns
to attribute names. The attributes are the values that can be accessed from the Java code.
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75
To accomplish the task of retrieving the paragraphs as mentioned above, you could declare the following DataQuery in your PDL file:
model tutorial;
// the first line indicates that it is a query and the name of the query
query paragraphMagazines {
// the next section maps the attributes to the java type so that the
// same type is returned regardless of which database driver is used.
BigDecimal magazineID;
BigDecimal paragraphID;
String issueNumber;
String text;
do {
select m.magazine_id, p.paragraph_id, issue_number, text
from magazines m, a, magazine_article_map ma, paragraphs p
where ma.magazine_id = m.magazine_id
and p.article_id = ma.article_id
} map {
magazineID = m.magazine_id;
paragraphID = p.paragraph_id;
issueNumber = m.issue_number;
text = p.text;
}
}
With this PDL definition, it should be easy to see how the following code does what is desired (remove
the &quot;\&quot; and make it all one line).
DataQuery query = SessionManager.getSession().retrieveQuery\
(&quot;tutorial.paragraphMagazines&quot;);
query.addEqualsFilter(&quot;issueNumber&quot;, &quot;5A&quot;);
while (query.next()) {
System.out.println((String)query.get(&quot;text&quot;));
}
9.4.1.2. Creating Data Objects
The method discussed for retrieving arbitrary information from the database is sufficient to do most
of what is needed. However, it is not very convenient since most Java code is written around using
DataObjects. Therefore, most developers want to be able to retrieve DataObjects directly from
the DataQuery. One way to do this is to create a new DataObject for each row returned by the query
and then populate that DataObject with the information retrieved. While this works, it is inefficient
and inelegant.
To solve this problem, the DataQuery allows the developer to create DataObjects directly from
the query. The objects can be defined within the query statement in a fashion similar to Attribute
declarations.
Suppose you want to get all magazines that have authors of articles whose last name starts with a given
sequence of characters. This is not a standard association because you are actually going through
two separate mapping tables. This could be done by getting all articles with authors that match the
criteria and then getting all magazines that contain the articles. However, this option would require
two separate database hits. Another option is to perform a query and then for every row create the
corresponding data object. A third option is to have the persistence layer create the data objects for
you. The following example shows how you can allow the persistence layer to perform the work for
you.
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The PDL is simply a Data Query with extra Attribute definitions (remove the &quot;\&quot; and make it all one
line).
query MagazineToAuthorMapping {
// the next two lines are declaring that objects will be returned
Magazine magazine;
Author author;
do {
select publications.name, issue_number, publication_id,
authors.first_name, authors.last_name, author_id
from magazines, publications, articles, authors,
magazine_article_map, article_author_map
where publications.publication_id = magazines.magazine_id
and magazine_article_map.magazine_id = magazines.magazine_id
and maagazine_article_map.article_id = article_author_map.\
article_id
and article_author_map.author_id = authors.author_id
} map {
// here we map the attributes of the objects to columns returned
// by the query.
magazine.name = publications.name;
magazine.issueNumber = magazines.issue_number;
magazine.id = publications.publication_id;
author.authorID = authors.author_id;
author.firstName = authors.first_name;
author.lastName = authors.last_name;
}
}
This can then be accessed with the Java like most other queries. The \ marks where the line has been
wrapped for printing purposes.
DataQuery query = SessionManager.getSession().retrieveQuery\
(&quot;tutorial.MagazineToAuthorMapping&quot;);
// the next line adds the filter so that we only get author’s whose last
// name begins with the letter &quot;s&quot;. Note that we are using a stanard filter
// because we need to perform a function on the column and we are positive
// that the value is not null.
Filter filter = query.addFilter(&quot;lower(lastName) like \
’%’ || :lastNamePrefix&quot;);
filter.set(&quot;lastNamePrefix&quot;, &quot;s&quot;);
while (query.next()) {
DataObject myAuthor = query.get(&quot;author&quot;);
DataObject myMagazine = query.get(&quot;magazine&quot;);
System.out.println(&quot;the author I retrieved is &quot; + myAuthor);
System.out.println(&quot;the magazine I retrieved is &quot; + myMagazine);
}
9.4.2. Data Operations
As mentioned previously, developers often need to be able to execute arbitrary DML statements that
do not fit nicely into the realm of data objects and data associations. To accommodate this need,
the system contains the concept of a DataOperation that can be used to execute arbitrary DML
statements or PL/SQL functions and procedures.
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9.4.2.1. Executing Arbitrary DML
Data Operations are similiar to DataQueries in both structure and use. However, while they are retrieved in a fashion similar to DataQueries, they are executed differently. After the query is retrieved,
the program can set bind variables, after which it is executed. Suppose you want to create a magazine
with ID 4 using all articles in the system that are not yet currently in a magazine. To do this, you could
create a new Magazine DataObject, give it an ID of 4, use a DataQuery to get all articles not already
in a magazine, add those articles to the magazine through the use of associations, and then save the
magazine. Alternately, you can use a DataOperation and execute a single query.
The DataOperation to execute the above query is structured in almost the same way as a DataQuery. In fact, it can even have an OPTIONS block (although it does not yet have any valid values for
the options block). However, since it does not return many different rows of results, it does not allow
attribute mappings before the first do block. The PDL can be defined as follows:
data operation createMagazine {
do {
insert into magazine_article_map (magazine_id, article_id)
select :magazineID, article_id from articles where not exists
(select 1 from magazine_article_map
where magazine_article_map.article_id = articles.article_id)
}
}
Now that the operation is defined, you can set the value of the bind variable magazineID to the
correct value and then execute the operation. This can be done with code such as the following (the \
marks where the line has been wrapped for printing purposes):
DataOperation operation = getSession().retrieveDataOperation\
(&quot;tutorial.createMagazine&quot;);
// we have to pass in an Integer instead of an int so that JDBC can
// handle it correctly
operation.setParameter(&quot;magazineID&quot;, new Integer(4));
operation.execute();
9.4.2.2. Executing PL/SQL
Developers often need to execute PL/SQL procedures and functions. Therefore, it is possible to execute both using a DataOperation with additional syntax. Arguments can be passed to functions ans
procedures using Parameter Binding.
Note
The methods described below do not allow users to return cursors from their PL/SQL functions. If
this is required, the recommended workaround is to use a CallableStatement directly and bypass
the persistence layer entirely.
9.4.2.2.1. PL/SQL Procedures
Suppose you want to execute the following PL/SQL procedure:
create or replace function myPLSQLProc(v_priority in integer)
as
begin
insert into magazines (magazine_id, title)
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select nvl(max(magazine_id), 0) + 1, :title from magazine_id;
end;
/
show errors
To do this, first include the above statement in your SQL file, so that it will be defined in the database
when your package is installed. Next, declare it in your PDL file using a DataOperation:
data operation DataOperationWithPLSQLAndArgs {
do {
select myPLSQLProc(:title) from dual
}
}
You can then execute this data operation just like any other data operation, after binding the title
variable.
It is also possible to use OUT parameters within the DataOperation. To do this, the only additional
requirement is for the developer to specify the JDBC type of all of the parameters within the query.
Suppose you want to copy the article with the highest ID into a new row with the ID that you pass
into the procedure, and you want back the ID for the row that was copied. You can declare a PL/SQL
procedure such as the following:
create or replace procedure DataOperationProcWithInOut(
v_new_id IN Integer,
v_copied_id OUT Integer)
as
begin
select max(article_id) into v_copied_id from articles;
insert into articles (article_id, title)
select v_new_id, title from articles where article_id = v_copied_id;
insert into article_author_map (article_id, author_id)
select v_new_id, author_id from article_author_map
where article_id = v_copied_id;
end;
/
show errors
Adding the JDBC type, the PDL to access this procedure appears as follows:
data operation DataOperationProcWithInOut {
do call {
DataOperationProcWithInOut(:newID, :copiedID)
} map {
newID : INTEGER;
copiedID : INTEGER;
}
}
To execute this in Java, you simply need to bind the variable and then retrieve the variable using the
get(String) method in a fashion similar to retrieving a value from a DataQuery. For instance, to
print out the value of the copiedID variable, the following code can be executed:
DataOperation operation = getSession().retrieveDataOperation
(&quot;tutorial.DataOperationProcWithInOut&quot;);
operation.set(&quot;newID&quot;, new Integer(4));
operation.execute();
Integer copiedID = (Integer)operation.get(&quot;copiedID&quot;);
System.out.println(&quot;The copied ID was [&quot; + copiedID.toString() + &quot;]&quot;);
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79
Note
The do call and OUT parameters are not available for Postgres because Postgres has not yet implemented CallableStatements or OUT parameters.
9.4.2.2.2. PL/SQL Functions
Retrieving a single value back from a function is almost identical to using OUT parameters for procedures. First, declare your PL/SQL in your SQL file. For example, you may define the following:
create or replace function DataQueryPLSQLFunction(v_article_id in integer)
return number
is
v_title varchar(700);
begin
select title into v_title from articles
where article_id = v_article_id;
return v_title;
end;
/
show errors
Next, you can define the function as a DataOperation within your PDL file, as follows:
data operation DataOperationWithPLSQLAndArgsAndReturnInPDL {
do call {
:title = DataQueryPLSQLFunction(:articleID)
} map {
title : VARCHAR(700);
articleID : Integer;
}
}
Finally, you can retrieve the value for title just like any normal data query, after binding the :articleID variable.
It is necessary to declare the types for each variable within the function whether or not it is an OUT
parameter.
9.5. Filtering, Ordering, and Binding Parameters
When retrieving information from the database, developers almost always need to be able to filter and
order the results that are returned. Therefore, DataQuery, DataCollection, and DataAssociationCursor objects allow for ordering and filtering. DataQuery and DataOperation also allow
developers to set arbitrary bind variables within the queries and DML statements. This document discusses how these features are implemented and how using the Filter can be overridden to use any
arbitrary filtering scheme.
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9.5.1. Filtering
9.5.1.1. Overview
The filtering system is complex, in that it allows developers to create complex expressions by combining filters, yet simple in that it provides convenience methods for developers with simple needs.
It is important to realize that by default, Filters simply filter the resulting data from the query. For
instance, if you have the following:
query myDataQuery {
BigDecimal articleID;
do {
select max(article_id) from articles
} map {
articleID = articles.article_id;
}
}
and then add the filter &quot;lower(title) like ’b%’&quot;, the new query will be:
select *
from (select max(article_id) from articles) results
where lower(title) like ’b%’
and not:
select max(article_id) from articles where lower(title) like ’b%’
This can clearly lead to different results.
9.5.1.2. Simple Filters
For simple filters, you should use the addEqualsFilter(String attributeName, Object
value) or the addNotEqualsFilter(String attributeName, Object value) methods to
filter a DataQuery, DataOperation, DataCollection, or a DataAssociationCursor object.
These methods take the name of the attribute and its value, create the correct SQL fragment, and bind
the variable. If the system is using Oracle or Postgres and the value is null, the system will create the
correct is null or is not null syntax.
In order to specify the filter, you must use the name of the Java Attribute, not the name of the database
column. The persistence layer automatically converts the property names to column names using the
property mappings defined in the PDL. This layer of abstraction is one of the features that allows developers to change column names without having to update Java code. For example, see the following
DataQuery defined in PDL (remove the &quot;\&quot; and make it all one line):
query UsersGroups {
String firstName;
String lastName;
String groupName;
do{
select *
from users, groups, membership
where users.user_id = membership.member_id and membership.group_id \
= groups.group_id
} map {
firstName=users.first_name;
lastName=users.last_name;
groupName=groups.group_name;
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}
To retrieve all users whose last name is &quot;Smith&quot;, do the following:
DataQuery query = session.retrieveQuery(&quot;UsersGroups&quot;);
query.addEqualsFilter(&quot;lastName&quot;, &quot;Smith&quot;)
while (query.next()) {
System.out.println(&quot;First name = &quot; + query.get(&quot;firstName&quot;) +
&quot;; Last name = &quot; + query.get(&quot;lastName&quot;) +
&quot;; Group = &quot; + query.get(&quot;groupName&quot;));
}
To get all users whose last name starts with &quot;S&quot;, use the addFilter method:
DataQuery query = session.retrieveQuery(&quot;UsersGroups&quot;);
// FilterFactory is explained below
query.addFilter\
(query.getFilterFactory().startsWith(&quot;lastName&quot;, &quot;S&quot;, false));
while (query.next()) {
System.out.println(&quot;First name = &quot; + query.get(&quot;firstName&quot;) +
&quot;; Last name = &quot; + query.get(&quot;lastName&quot;) +
&quot;; Group = &quot; + query.get(&quot;groupName&quot;));
}
9.5.1.3. Complex Filters
For more complex queries, it is helpful to understand the role of each interface that deals with Filters.
— This class represents a single expression for part of a &quot;where&quot; clause. For instance, a
Filter could be &quot;foo = :bar&quot; with a value associated with &quot;bar&quot; (e.g. &quot;foo = 3&quot;).
• Filter
— This class extends Filter and provides the ability to add filters together
using the AND and OR keywords.
• CompoundFilter
— This class is responsible for handing out filters. It has methods such as &quot;simple&quot;, &quot;equals&quot;, &quot;notEquals&quot;, &quot;lessThan&quot;, &quot;greaterThan&quot;, &quot;startsWith&quot;, &quot;contains&quot;, and &quot;endsWith&quot;.
If a user is using Oracle or Postgres, all these methods check whether the value is null, and if so,
act correctly (e.g., use &quot;foo is null&quot; instead of &quot;foo = null&quot;).
• FilterFactory
• DataQuery —
This class allows you to add filters as well as get a reference to the FilterFactory. If
you need a FilterFactory but do not have a DataQuery, use Session.getFilterFactory().
If you want to filter the query based on certain conditions, you can incrementally build up your query
as follows:
DataQuery query = session.retrieveQuery(&quot;UsersGroups&quot;);
FilterFactory factory = query.getFilterFactory();
if (beginLetter != null) {
query.addFilter(factory.lessThan(&quot;firstLetter&quot;, beginLetter, true));
}
if (lastLetter != null) {
query.addFilter(factory.greaterThan(&quot;firstLetter&quot;, beginLetter, true));
}
while (query.next()) {
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System.out.println(&quot;First name = &quot; + query.get(&quot;firstName&quot;) +
&quot;; Last name = &quot; + query.get(&quot;lastName&quot;) +
&quot;; Group = &quot; + query.get(&quot;groupName&quot;));
}
Now suppose you want to get all users with a last name that is the same as the variable lName or
is Smith, and with a first name that matches the variable fName or is John. You could do this as
follows:
DataQuery query = session.retrieveQuery(&quot;UsersGroups&quot;);
FilterFactory factory = query.getFilterFactory();
Filter filter1 = factory.or().addFilter(factory.equals(&quot;lastName&quot;, lName))
.addFilter\
(factory.equals(&quot;lastName&quot;, &quot;Smith&quot;));
Filter filter2 = factory.or().addFilter(factory.equals(&quot;firstName&quot;, fName))
.addFilter\
(factory.equals(&quot;firstName&quot;, &quot;John&quot;));
query.addFilter(factory.and().addFitler(filter1).addFilter(filter2));
while (query.next()) {
System.out.println(&quot;First name = &quot; + query.get(&quot;firstName&quot;) +
&quot;; Last name = &quot; + query.get(&quot;lastName&quot;) +
&quot;; Group = &quot; + query.get(&quot;groupName&quot;));
}
These could also have been chained together in order to avoid creating any Filter variables, but this
was not done here for clarity.
Finally, if you want to add a bunch of &quot;foo = :foo&quot; statements to a query, you can use the convenience
methods provided by DataQuery. These methods delegate to FilterFactory and therefore handle the
Oracle null problem. For instance:
DataQuery query = session.retrieveQuery(&quot;UsersGroups&quot;);
if (includeFirstName) {
query.addEqualsFilter(&quot;firstName&quot;, fName);
}
if (includeLastName) {
query.addEqualsFilter(&quot;firstName&quot;, fName);
}
while (query.next()) {
System.out.println(&quot;First name = &quot; + query.get(&quot;firstName&quot;) +
&quot;; Last name = &quot; + query.get(&quot;lastName&quot;) +
&quot;; Group = &quot; + query.get(&quot;groupName&quot;));
}
Note
When setting dates, java.util.Date objects should be used instead of java.sql.Date objects because
java.sql.Dates do not have hours, minutes, or seconds.
When filtering a query that returns data objects (as opposed to simple java types), you must prepend
the name of the object attribute. For instance, if you want to retrieve all uses using a query, you would
follow the example below. In practice, you want to retrieve a DataCollection from the Session
but we are using a query here for demonstration purposes.
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query retrieveAllUsers {
User myUser;
do {
select user_id, first_name, last_name from users
} map {
user.id = users.user_id;
user.firstName = users.first_name;
user.lastName = users.last_name;
}
}
DataQuery query = session.retrieveQuery(&quot;retrieveAllUsers&quot;);
// notice how the attribute name corresponds directly to what
// in the map&quot; section of the query and is actully
// the object type . attribute name
query.addEqualsFilter(&quot;user.firstName&quot;, fName);
while (query.next()) {
DataObject user = query.get(&quot;user&quot;);
System.out.println(&quot;First name = &quot; + user.get(&quot;firstName&quot;) +
&quot;; Last name = &quot; + user.get(&quot;lastName&quot;) +
&quot;; Group = &quot; + user.get(&quot;groupName&quot;));
}
9.5.1.4. Restricting the number of rows returned
One common feature that is requested of queries, collections, and associations is to be able to restrict
the number of rows that are returned. Specifically, in order to create any sort of pagination or to break
up a large set of results in to a series of smaller sets it is necessary to restrict the number of rows
returned.
Restricting the number of rows a query returns is easy. To do so, you can simple call
setRange(Integer, Integer) on the data query is question. For instance, if I want results 10-19
for a qury, I can do the following:
DataQuery query = session.retrieveQuery(&quot;retrieveAllUsers&quot;);
query.setRange(new Integer(10), new Integer(20));
while (query.next()) {
DataObject user = query.get(&quot;user&quot;);
System.out.println(&quot;First name = &quot; + user.get(&quot;firstName&quot;) +
&quot;; Last name = &quot; + user.get(&quot;lastName&quot;) +
&quot;; Group = &quot; + user.get(&quot;groupName&quot;));
}
9.5.1.5. Filtering Using Subqueries
The filtering methods described so far handle most situations. However, sometimes developers need
the ability to filter based on the results of a subquery. Therefore, the persistence layer provides a
mechanism to allow developers to use named queries within filters. Specifically, this is useful within
IN clauses and EXISTS clauses.
Suppose that you want to retrieve all articles written by authors whose last name begins with the letter
&quot;b&quot;. One easy way to avoid duplicates is to use an IN clause. To perform this operation, you can create
the following two DataQueries:
query retrieveArticlesBasedOnAuthor {
BigDecimal authorID;
do {
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select article_id
from authors, author_article_map
where authors.author_id = author_article_map.author_id
and lower(last_name) like :lastName || ’%’
} map {
authorID = authors.author_id;
}
}
query retrieveSelectedArticles {
BigDecimal articleID;
String title;
do {
select article_id, title from articles
} map {
articleID = articles.article_id;
title = articles.title;
}
}
Next, simply retrieve one query and add the other query as part of the filter, as follows (remove the \
and make it all one line):
Session session = SessionManager.getSession();
DataQuery query = \
session.retrieveQuery(&quot;tutorial.retrieveSelectedArticles&quot;);
Filter filter = query.addInSubqueryFilter(&quot;articleID&quot;, \
&quot;tutorial.retrieveAuthorsWithParam&quot;);
// we have to set the value for &quot;lastName&quot; since it is a bind variable
// in the subquery we added.
filter.set(&quot;lastName&quot;, &quot;b&quot;);
System.out.println\
(&quot;The following articles have at least one author whose &quot; +
&quot;last name starts with ’b’&quot;);
while (query.next()) {
System.out.println(query.get(&quot;title&quot;));
}
The code above will actually execute the following SQL:
select article_id, title from articles
where article_id in (select article_id
from authors, author_article_map
where authors.author_id = \
author_article_map.author_id
and lower(last_name) like ? || ’%’
with ? = &quot;b&quot;
Note
While there are other, possibly better ways to obtain the same result, this example is used to demonstrate how the feature works, not as an authoritative example of writing queries.
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9.5.1.6. Filtering Using Functions
The filtering methods discussed so far work well when the developer only needs to filter directly off
of columns or values. However, they do not work well if the developer wants a case-insensitive filter
or needs to use some other function to manipulate the data in the columns.
To meet this need and to appropriately handle null values, the system provides a method within FilterFactory named compare that allows developers to pass in two expressions and have the system
compare them to each other.
The most common use case for this is a case-insensitive comparison where the developer wants to
know whether a string exists in a column, but does not care about the case. For instance, suppose a developer wants to retrieve all articles titled &quot;Disaster Strikes,&quot; but does not care about the capitalization.
He could use use the following code to achieve this:
DataCollection pub = SessionManager.getSession().retrieve(&quot;tutorial.Articles&quot;);
Filter filter = pub.addFilter(pub.getFilterFactory().compare(&quot;upper(title)&quot;,
FilterFactory.EQUALS,
&quot;:title&quot;));
// we set the title to all upper case so that we do not make oracle do
// it for us which would be slower
filter.set(&quot;title&quot;, &quot;DISASTER STRIKES&quot;);
If the developer actually wants all articles with either the word &quot;Disaster&quot; or &quot;Strikes,&quot; he can do the
following:
DataCollection pub = \
SessionManager.getSession().retrieve(&quot;tutorial.Articles&quot;);
FilterFactory factory = pub.getFilterFactory();
Filter disasterFilter = \
factory.compare(&quot;upper(title)&quot;, FilterFactory.CONTAINS,
&quot;:disasterTitle&quot;));
filter.set(&quot;disasterTitle&quot;, &quot;DISASTER&quot;);
Filter strikesFilter = \
factory.compare(&quot;upper(title)&quot;, FilterFactory.CONTAINS,
&quot;:strikesTitle&quot;));
filter.set(&quot;disasterTitle&quot;, &quot;STRIKES&quot;);
pub.addFilter(factory.or()
.addFilter(disasterFilter)
.addFilter(strikesFitler));
The important thing to realize is that it this method will handle problem with null values faced by
Oracle and Postgres, whereas using a standard simple filter will not.
9.5.2. Ordering
Use the addOrder(String order) method to order a DataQuery, DataCollection, and a
DataAssociationCursor object. The addOrder method takes a String as its only parameter
and the format of the string is the optional object type following by a dot and then then required
attribute name ([ object type name .] attribute ) you wish to order by.
The string parameter passed to the addOrder(String order) method is used in an ORDER BY
clause, which is appended to the SELECT statement. The order is specified by constructing a string
representing the ORDER BY clause, but instead of specifying column names, you specify attribute
names. The persistence layer automatically converts the attribute names to column names using the
property mappings defined in the PDL. For example, see the following DataQuery defined in PDL
(remove the &quot;\&quot; and make it all one line):
query UsersGroups {
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String firstName;
String lastName;
String groupName;
do{
select *
from users, groups, membership
where users.user_id = membership.member_id and membership.group_id \
= groups.group_id
} map {
firstName=users.first_name;
lastName=users.last_name;
groupName=groups.group_name;
}
}
You can order this query by the user’s last name, as follows:
DataQuery query = session.retrieveQuery(&quot;UsersGroups&quot;);
query.addOrder(&quot;lastName asc&quot;);
while (query.next()) {
System.out.println(&quot;First name = &quot; + query.get(&quot;firstName&quot;) +
&quot;; Last name = &quot; + query.get(&quot;lastName&quot;) +
&quot;; Group = &quot; + query.get(&quot;groupName&quot;));
}
Finally, you can build up the ORDER BY string in the same way that you build up a filter. For instance:
DataQuery query = session.retrieveQuery(&quot;UsersGroups&quot;);
query.addOrder(&quot;lastName asc&quot;)
if {careAboutGroupName} {
query.addOrder(&quot;groupName&quot;);
}
while (query.next()) {
System.out.println(&quot;First name = &quot; + query.get(&quot;firstName&quot;) +
&quot;; Last name = &quot; + query.get(&quot;lastName&quot;) +
&quot;; Group = &quot; + query.get(&quot;groupName&quot;));
}
The ORDER BY string is any valid ORDER BY clause, except that you specify property names, not
column names.
9.5.3. Binding Parameters
Use the setParameter(String parameterName, Object value) method to bind an arbitrary
variable within a DataQuery, DataOperation, DataAssociationCursor, or DataCollection.
The method getParameter(parameterName) allows you to retrieve the value of a set parameter.
The setParameter takes in a string that should match the string within the defined SQL. The Object
it takes should specify the value.
This functionality is useful for complicated queries that involve embedding parameters. For example,
see the following DataQuery defined in PDL (bind variables are in bold):
query CategoryFamily {
Integer level;
BigDecimal categoryID;
String name;
String description;
Boolean isEnabled;
do {
select l, c.category_id, c.name, c.description, c.enabled_p
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from (select level l, related_category_id
from (select related_category_id, category_id
from cat_category_category_map
where relation_type = :relationType)
connect by prior related_category_id = category_id
start with category_id = :categoryID) m,
cat_categories c
where c.category_id = m.related_category_id
} map {
level = m.l;
categoryID = c.category_id;
name = c.name;
description = c.description;
isEnabled = c.enabled_p;
}
}
This query first retrieves all mappings that are of a particular type (e.g., &quot;child&quot; mappings as opposed
to &quot;related&quot; mappings). It then does a &quot;connect by&quot; to get all the parents (or all the related categories).
Finally, it joins this result with the original categories table so that it can have the name, categoryID,
description, and isEnabled for each of the selected categories. Without being able to set the
categoryID and relationType variables, you could not perform this query. Creating a separate
query for each kind of relationType does work, but there is no way to account for every possible
categoryID.
After the query is defined, it can be used as follows:
DataQuery query = session.retrieveQuery(&quot;CategoryFamily&quot;);
query.setParameter(&quot;relationType&quot;, &quot;child&quot;);
query.setParameter(&quot;categoryID&quot;, &quot;3&quot;);
while (query.next()) {
System.out.println(&quot;We retrieved Category &quot; + query.get(&quot;name&quot;)) +
&quot;with ID = &quot; + query.get(&quot;categoryID&quot;));
}
9.5.3.1. Binding Collection Parameters
Thus far, the document has discussed binding parameters that contain a single value, that is, parameters
that are used in comparison clauses. While these types of parameters cover most cases, sometimes you
will want to be able to have bind variables that represent many different values. Specifically, you may
want to be able to get rows that meet specific criteria and are IN a given set of rows. To provide this
functionality, the system has the ability to take a java.util.Collection as the value for a bind variable
and then expand the Collection so that it works correctly.
For instance, if you want all Articles whose IDs were in a given collection, you can write a method
such as the following (remove the &quot;\&quot; and make it all one line):
public DataCollection retrieveArticles(Collection articlesToRetrieve) {
DataCollection articles = SessionManager.getSession().retrieve\
(&quot;tutorial.Articles&quot;);
Filter filter = articles.addFilter(&quot;id in :articlesToRetrieve&quot;);
filter.set(&quot;articlesToRetrieve&quot;, articlesToRetrieve);
return articles;
}
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9.5.4. How it Works
You may be wondering how to add filters and bind variables after retrieving the query. The persistence
system does not actually execute the required SQL query until the first call to next(). Therefore, the
DataQuery (or DataCollection or DataAssociationCursor) can be passed around and have
Filters and ORDER BY statements added and variables bound before the first element is retrieved.
Then, when the first element is retrieved, the query is executed and the code can no longer add or
remove filters or ordering criteria.
9.6. Common Mistakes
9.6.1. Introduction
As developers use the persistence layer of the WAF, several types of errors are made by many developers. This document tries to highlight some of those errors to help with debugging tasks. Another
document that may be of interest to developers having problems with persistence is the Section 9.10
Frequently Asked Questions.
9.6.2. Use of Semi-Colons; Invalid Character Error
One of the most common and most easily fixed errors is that of an invalid character. The error is
typically something such as:
com.arsdigita.persistence.PersistenceException: ORA-00911: invalid character
This error is caused because the developer accidentally included a semi-colon at the end of a SQL
statement. For instance, the following retrieve event will cause the above error because of the
semi-colon (in bold) at the end:
retrieve {
do {
select publication_id, name
from publications
where publication_id = :id;
} map {
id = publications.publication_id;
name = publications.name;
}
}
To fix the error, simply remove the semi-colon so that the event definition appears as follows:
retrieve {
do {
select publication_id, name
from publications
where publication_id = :id
} map {
id = publications.publication_id;
name = publications.name;
}
}
This error occurs is because the query is fed directly to the database using the JDBC driver, which
does not exptect a trailing semi-colon.
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9.6.3. Incorrect Attribute Mappings
When you receive an error indicating that an attribute cannot be found or an attribute name is invalid,
make sure that there are no typos. Simple typos cannot be caught by the compiler and cause many
errors.
9.6.4. Problems with Transactions
Typically, two types of mistakes occur when dealing with Transactions within the WAF.
The first type of mistake is trying to access Data Objects (and hence the database) outside of a transaction. This typically happens when the developer tries to write a custom dispatcher that bypasses
the standard WAF dispatcher and does not remember to include transaction management. To fix this,
make sure that the custom dispatcher properly opens and closes transactions using appropriate WAF
APIs.
The second type of mistake is the exact opposite of the first: trying to nest transactions. Unless you
have written a custom dispatcher that bypasses the standard WAF dispatcher, you should never have
to open or close a transaction. Trying to do so within the standard framework of the WAF will result
in an error. In almost all cases, developers building on top of the WAF should not try to manage their
own transactions.
For more information, see the document on Section 9.7 Transaction Management.
9.6.5. Join Paths
Common problems:
•
Non-continuous join paths -- the second column’s table in each join path element must match the
table of the next join path element’s first column. That is, the path must look somthing like join
A.B to C.D, join C.E to E.F In this example, table C is the last table of the first half and the
first table of the second half.
•
Join paths are too long -- MDSQL only supports join paths composed of 1 or 2 join path elements.
If paths are longer than that, it becomes impossible to generate events correctly given the current
implementation.
•
Join path does not start in the primary table -- a join path must always start in the same table as the
reference key or object key. If it does not, there is a gap and the event cannot be generated.
9.6.6. Dynamic DDL Generation
Dyanmic DDL Generation works well when the PDL is specified correctly. However, it is easy to think
that the PDL is written to represent the model correctly when in fact you are missing a simple item to
two. Below are some symptoms that you may see with your generated DDL and some suggestions as
to how you may be able to fix them.
Data Model Problem
Likely Cause in PDL
Missing columns
Properties were specified without a column or
join path
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Data Model Problem
Likely Cause in PDL
Missing foreign keys
Object Model doesn’t use associations, but data
model does, e.g. Message object has
BigDecimal authorID property instead of User
author property, in these cases an easy fix is to
create the author association without removing
the authorID attribute so that existing java code
continues to work.
Missing not null
The property in PDL is [0..1] when it should be
[1..1].
Extra not null
The property in PDL is [1..1] when it should be
[0..1].
Missing on delete cascade
The property in PDL should be declare
component or composite.
Missing unique constraint
The property(ies) in PDL should be declared
unique.
9.6.7. Debugging Persistence
When developing code using persistence, you may have a difficult time tracking down the
reason for a PersistenceException. Turning up the logging level can help you understand
what is going on. The following Log4J loggers com.redhat.persistence.Session and
com.redhat.persistence.engine.rdbms can be turned to the info log level to help see what is
going on. The latter will log all SQL being sent to the database.
9.7. Transaction Management
Within WAF, the Servlet Dispatchers handle all transactions for the developer. This document clarifies
the decisions that have been made regarding transactions within the WAF, and briefly discusses how
to manage transactions outside of the WAF.
9.7.1. Transactions within the WAF
The WAF imposes several restrictions on the developer that are important to understand:
•
Only one transaction may be open at a time for a given thread. More concretely, it is not possible
to nest transactions.
•
Writable Data Objects cannot be cached across transactions, because aborting a transaction requires
some way to either rollback or invalidate all DataObjects using the transaction. However, it is
possible to cache read-only data objects since they are loaded from the database a single time and
then never modified and they never again need to access the database. However, when doing this, it
is important that all read-only objects are removed from memory when a writable object is retrieved.
One feature to realize is that if a SQLException is thrown when using Postgres then the transaction is
aborted and it is no longer possible to interact with the database. Therefore, it is necessary to check
for all conditions that could cause an error to arise before actually making a call to the database.
When programming in the WAF, unless you are writing a dispatcher or initializer, you will most likely
not need to deal with transactions. However, if you do, the process is simple and is outlined in the next
section.
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9.7.2. Manual Transaction Management
When you manage your transactions locally, your starting point is the SessionManager class. From
there, you can get access to the Session class and then to the Transaction. Specifically, the Session
provides access to the TransactionContext, which has methods for beginning a transaction, committing
a transaction, and aborting a transaction. For example, the following code will open a transaction,
execute the necessary code and then either commit or abort the transaction:
import com.arsdigita.persistence.Session;
import com.arsdigita.persistence.SessionManager;
import com.arsdigita.persistence.TransactionContext;
Session session = SessionManager.getSession();
TransactionContext txn = session.getTransactionContext();
try {
txn.beginTxn();
// do some work here
txn.commitTxn();
} catch (Exception e) {
txn.abortTxn();
}
Transactions cannot be nested. If you have to make sure that you are in a transaction, use the inTxn()
method of TransactionContext, as in the following example:
import com.arsdigita.persistence.Session;
import com.arsdigita.persistence.SessionManager;
import com.arsdigita.persistence.TransactionContext;
Session session = SessionManager.getSession();
TransactionContext txn = session.getTransactionContext();
boolean openedTransaction = false;
try {
if (!txn.inTxn()) {
openedTransaction = true;
txn.beginTxn();
}
// do some work here
if (openedTransaction) {
txn.commitTxn();
}
} catch (Exception e) {
if (openedTransaction) {
txn.abortTxn();
}
}
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9.8. Link Attributes
When modeling many real-world problems, it is common to encounter situations that require associating data with a link between two objects. This document describes how to model these situations
using the persistence system.
9.8.1. Introduction
When creating a model for use in a particular domain, there are usually cases in which a simple
association between two object types will not suffice. A Group may contain Users through a members
Association (see Section 9.3 Associations), and for each member that Group may want to record the
date on which the User became a member of the Group. This is a case in which the link between
two objects must carry more information than just that the two objects are associated. The UML
terminology for this is a qualified association and it is described with the following model.
____________
____________
|
Group
|
|
User
|
|------------|
|------------|
|
| n
n |
|
|
|------------------------&gt;|
|
|
|
|
members |
|
|____________|
|
|____________|
|
|
|
________|________
|
|
|-----------------|
| membershipDate |
|
|
|_________________|
A model like the one depicted above can be created in sql with the following 3 tables.
create table groups (
group_id
integer primary key;
name
varchar(300);
....
);
create table users
user_id
name
email
....
);
(
integer primary key;
varchar(300);
varchar(100);
create table group_member_map (
group_id
integer references groups;
member_id
integer references users;
membership_date date default sysdate;
primary key (group_id, member_id);
);
This association can then easily be transformed to PDL through the use of the association keyword.
When defining an association between two objects using the association block, it is possible to add
extra properties that can store information associated with a particular link between two objects.
object type Group {
BigInteger[1..1] id = groups.group_id;
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String[1..1]
// ...
93
name = groups.name;
}
object type User {
BigInteger[1..1] id = users.user_id;
String[1..1]
name = users.name;
String[1..1]
email = users.email;
// ...
}
association {
Group[0..n] groups = join users.user_id to \
group_member_map.member_id,
join group_member_map.group_id to \
groups.group_id;
User[0..n] members = join groups.group_id to \
group_member_map.group_id,
join group_member_map.member_id to \
users.user_id;
Date[1..1]
membershipDate = group_member_map.membership_date;
}
Note
In this case, all events are auto-generated and will only work if the link attribute (in this case, membershipDate) is defined within the mapping table. If the DDL generator is used, the above association
definition will create the correct mapping table.
It is also possible to have a link attribute that returns a full object type (e.g. another User) rather than
a simple object type (e.g. a Date). Everything in this example is the same if you replace Date with
User. The only extra assumption made is that the full object type (e.g. User) only has a single Object
Key and that key is the item stored in the mapping table (e.g. user_id must be stored in the mapping
table in the case of User).
9.8.2. Link Attributes API
Once the PDL has been written to describe link attributes, the java API may access the values using
the following methods (remove the &quot;\&quot; and make it all one line):
• DataObject DataAssociation.add(DataObject object)
—
http://rhea.redhat.com/doc/waf/6.0/api/com/arsdigita/persistence/\
DataAssociation.html#add(com.arsdigita.persistence.DataObject)
• Object DataAssociationCursor.getLinkProperty(java.lang.String)
—
http://rhea.redhat.com/doc/waf/6.0/api/com/arsdigita/persistence/\
DataAssociationCursor.html#getLinkProperty(java.lang.String)
—
http://rhea.redhat.com/doc/waf/6.0/api/com/arsdigita/persistence/\
DataAssociationCursor.html#getLink()
• classname
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9.8.2.1. Creating and Initializing Links
The DataAssociation.add(DataObject object) method is used when creating a link between
two objects. If the association was defined with the association keyword, this method returns the link
DataObject. The link DataObject can then be used to set any link attributes that have been defined.
This is illustrated in the following example:
// Put the current session in a variable for convenience.
Session ssn = SessionManager.getSession();
// Get a user.
DataObject user = ssn.retrieve(new OID(&quot;User&quot;, ...));
// Get a group.
DataObject group = ssn.retrieve(new OID(&quot;Group&quot;, ...));
// Get the &quot;members&quot; association so that we can add a member to the
// group.
DataAssociation members = (DataAssociation) group.get(&quot;members&quot;);
// Add the user to the association.
DataObject link = members.add(user);
java.util.Date now = new java.util.Date();
link.set(&quot;membershipDate&quot;, now);
// Persist the changes.
group.save();
Note
Only group.save() is called to persist the changes. Changes to the links are automatically persisted
when the parent object is saved.
9.8.2.2. Reading Link Attributes
The DataAssociationCursor.getLinkProperty(java.lang.String) method can be used to
read the values of a link attribute while iterating over a cursor.
// Put the current session in a variable for convenience.
Session ssn = SessionManager.getSession();
// Get a group.
DataObject group = ssn.retrieve(new OID(&quot;Group&quot;, ...));
// Get the members association.
DataAssociation members = (DataAssociation) group.get(&quot;members&quot;);
// Iterate over the members of the group and print out the
// membership date.
DataAssociationCursor cursor = members.getDataAssociationCursor();
while (cursor.next()) {
// Fetch the users email for the current row.
String email = cursor.get(&quot;email&quot;);
// Fetch the link property for the current row.
java.util.Date membershipDate =
(java.util.Date) cursor.getLinkProperty(&quot;membershipDate&quot;);
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System.out.println(email + &quot;: &quot; + membershipDate);
}
9.8.2.3. Updating Link Attributes
The DataAssociationCursor.getLink() method can be used to fetch the DataObject that represents a link. This DataObject can then be used to modify the link and persist the results.
// Put the current session in a variable for convenience.
Session ssn = SessionManager.getSession();
// Get a group.
DataObject group = ssn.retrieve(new OID(&quot;Group&quot;, ...));
// Get the members association.
DataAssociation members = (DataAssociation) group.get(&quot;members&quot;);
// Iterate over the members of the group and modify each link.
DataAssociationCursor cursor = members.getDataAssociationCursor();
while (cursor.next()) {
// Fetch the link object for the current row.
DataObject link = cursor.getLink();
// Get the membership date from the link data object.
java.util.Date oldDate = (java.util.Date) \
link.get(&quot;membershipDate&quot;);
// Incrememnt the membership date by 1 millisecond.
java.util.Date newDate = new \
java.util.Date(oldDate.getTime() + 1);
// Set the new date
link.set(&quot;membershipDate&quot;, newDate);
}
// Persist all the changed links.
group.save();
Note
Only group.save() is called to persist the changes. Changes to the links are automatically persisted
when the parent object is saved.
9.8.2.4. Filtering and Ordering based on Link Attributes
To access the values of a link attribute when filtering or setting the order of a data association, simply
put the special link prefix in front of the link attribute name.
// Put the current session in a variable for convenience.
Session ssn = SessionManager.getSession();
// Get a group.
DataObject group = ssn.retrieve(new OID(&quot;Group&quot;, ...));
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// Get the members association.
DataAssociation members = (DataAssociation) group.get(&quot;members&quot;);
// Iterate over new members of the group.
DataAssociationCursor cursor = members.getDataAssociationCursor();
// Get yesterday’s date.
java.util.Date yesterday =
new java.util.Date(System.currentTimeMilis() - \
1000 * 60 * 60 * 24);
// Restrict to recent members
Filter f = cursor.addFilter(&quot;link.membershipDate
f.set(&quot;date&quot;, yesterday);
:date&quot;);
// Order by membership date, descending
cursor.setOrder(&quot;link.membershipDate desc&quot;);
while (cursor.next()) {
...
}
9.9. Dynamic Object Types
Thus far, the documentation has assumed that developers know the types of objects that they will
be dealing with at compile time. More concretely, it has assumed that all SQL table definitions and
PDL files have already been defined by the developer. In some situations, however, this assumption is
invalid.
Sometimes developers want to provide site administrators with an interface to create their own types
of objects and store custom information within the database. Since it is not possible to anticipate all
information anyone will ever want to store in the system and it is not feasible to require developers
to manually create all types, the system contains the notion of a DynamicObjectType that provides
developers with the ability to create data schemas (and persist data to that schema) at run time. This
is one of the main motivations of the Metadata-Driven SQL.
The implementation of dynamically storing information has been broken into two parts. The first
part, dynamically creating new object types, uses the DynamicObjectType class. The second part,
dynamically associating objects to each other, is handled by DynamicAssociation.
9.9.1. Using Dynamic Object Types
In order to provide developers with the ability to declare objects at run time instead of at compile
time, the persistence system has the notion of a DynamicObjectType. A Dynamic Object Type allows
users to dynamically create and modify Object Types. It can be used to create a subtype of an existing
object type, add and remove Attributes and RoleReferences, and perform many other tasks related to
the new object type.
The way that this is done is relatively simple. The developer uses methods within the class to set the
Model and object type name and create attributes. When the code saves the current object type, it does
the following:
1. Creates the DDL that needs to be executed to store information about the specific object type.
2. Generates the PDL that needs to be stored so that the object type will be instantiated when the
server restarts.
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3. Generates the events for storing information in the schema in memory so that the ObjectType
returned can be used within DataObjects.
4. Executes the DDL to create the schema. Unfortunately, this causes the system to commit the
current transaction, so it is important that you do not do anything else in the same transaction as
saving the DynamicObjectType.
5. Assuming the DDL executed successfully, saves the PDL that was generated to a table within
the database. The information in this table is then read in on every server startup, so that the
DynamicObjectTypes essentially become permanent.
6. Regenerates events for any children of this object type that may have been affected by any
changes that were made.
9.9.2. Dynamic Associations
The DynamicObjectType supports creating new object types. However, it does not allow the dynamic
creation of associations that involve static object types. Specifically, if a developer wanted to dynamically create an association between Users and the Publications that they read, the only way to do that
would be to add that information to the PDL file, recompile and restart the server. To address this
problem, the system provides a DynamicAssociation class.
This class saves information about the association following approximately the same steps as the DynamicObjectType. The main difference between the classes, besides the types of events they generate,
is that the DynamicAssociation can be used to map two dynamically defined Object Types, two statically defined Object Types, or one dynamically defined Object Type and one statically defined Object
Type. This is in contrast to the DynamicObjectType that only deals with dynamically defined Object
Types.
9.10. Frequently Asked Questions
This document contains a list of the most frequently asked questions concerning the WAF persistence
layer. For terminology and definitions, please see the Persistence Glossary.
1. General Questions
1.1. Why does the Red Hat WAF have a persistence layer? Why doesn’t it just create the SQL
when and where it is needed?
A persistence layer has been developed as part of the WAF for the purpose of encapsulating
database access routines. This is desirable for at least two reasons: abstraction and database
independence. By encompassing the SQL statements in Java objects, the database access routines are developed in a scalable environment. Also, the applications are isolated from the
schema changes (which may occur in future versions) since the database access routines are
encapsulated by a standard API. The second reason, database independece, is desirable because it means that the Java code can easily be ported from one database to another by changing a small set of centrally located files (as opposed to modifying every file that interacts with
the database).
1.2. Why does the Red Hat WAF have a persistence layer instead of just using standard EJB?
Why is Red Hat reinventing the wheel?
WAF is primarily a framework for building web applications, and Red Hat’s reasoning for
its current architectural direction is best summarized by Sun’s own J2EE Blueprints at
http://java.sun.com/blueprints/corej2eepatterns/Patterns/DataAccessObject.html.
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In addition, there are numerous examples that one could concoct where an EJB server (at least
initially) could be deemed to be an overkill given the problem being tackled. This is the sledgehammer-to-crack-a-nut problem. In essence, the J2EE specification does not mandate a 2, 3,
or multitier application model, nor realistically could it do so. The point is that it is important
to use appropriate tools for a given problem space.
Given that the most common usage for WAF deployment is, to use Sun’s term, the &quot;Webcentric application scenario&quot;, Red Hat opted for the &quot;3-tier Web-centric&quot; architecture, in which
&quot;[t]he Web container is essentially hosting both presentation and business logic, and it is assumed that JDBC (and connectors in the future) will be used to access the EIS resources.&quot;
Coarse-grained interoperation of WAF with other systems would certainly be a sound application of EJB or JMS. However, Red Hat does not currently have clear requirements in this area.
More activity is anticipated in this area during future WAF implementations, initiated both by
Red Hat and by others building on top of WAF.
(As an aside, commercial J2EE containers such as WebLogic and Oracle’s 9i typically make
it a goal to provide a &quot;simple mechanism for balancing load across several machines without
too much thinking,&quot; even when you are only using the Servlet API, as opposed to EJBs.)
Regarding the other reasons for using EJBs outside of distributed objects, the following points
should clarify the extent to which Red Hat is &quot;reinventing the wheel&quot;:
1. Persistence: There are two standard types of persistence: Bean-Managed Persistence
(BMP) and Container-Managed Persistnce (CMP). BMP does not provide much advantage, and CMP, unfortunately, does not provide automatic SQL generation. In short, the
WAF persistence layer is designed to address a different set of requirements than CMP.
2. Connection pooling: Red Hat is not reinventing connection pooling; rather, its code is
writtten against the J2EE-standard API for connection pooling, the JDBC 2.0 Optional
Package at http://java.sun.com/products/jdbc/articles/package2.html.
3. Transaction monitoring: EJB’s declarative-style transaction management is one of its
more attractive features, but not compelling enough for Red Hat to make it the deciding
factor in using EJBs. Red Hat does not &quot;reinvent&quot; transaction management, either; it
simply leaves the applications responsible for managing transactions.
Red Hat has found, through input from prospective customers, partners, and analysts, that the
market perspective on the necessity and appeal of the &quot;full J2EE architecture&quot; is not clear-cut.
Being able to run WAF atop a J2EE web container alone has benefits of its own: simplicity of
development and deployment, low run-time overhead, and broad availability of stable opensource/affordable implementations. In other words, 3-tier Web-centric is quite defensibly the
appropriate tool for Red Hat’s primary problem space.
1.3. What are the primary benefits/goals of the persistence API?
The persistence API provides the following benefits:
•
It provides an abstraction for physical data models for greater database independence.
•
It isolates the java classes from data model changes (e.g., if a column is renamed, no Java
code must be changed).
•
It provides support for user-defined object types.
•
It decreases the amount of time it takes to implement a new object type.
•
It can automatically generate SQL statements that can be run on different databases. Thus,
it is possible to write one PDL file that can be used on N databases. Without persistence,
a developer may be required to write N different DDL scripts and then N different sets of
SQL statements to use the tables.
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2. Developer Specific Questions
2.1. I am new to the persistence API. Where do I start?
Start with this book’s table of contents which lists all available persistence documents. In
addition, the Section 10.2 Domain Objects Tutorial introduces the API used by the WAF and
provides you with code samples for implementing your own Domain Objects.
Additionally, you may want to consult the document on Section 9.2 Beginning With Data
Objects, as well as material on Section 9.5 Filtering, Ordering, and Binding Parameters.
2.2. If I am creating an object type what kind of metadata do I need to define?
The best place to find a full explaination and examples is in the Section 9.2.3 Defining an
Object Type in PDL. However, as a short summary, you must specify the following:
•
For each attribute:
•
A mapping of the attribute to the database column in which it resides.
•
The SQL type of the attribute. For instance, if the data type of the attribute is a string, the
SQL type might be VARCHAR(20) or VARCHAR(4000) or even CLOB.
•
For each association, it is important to specify the Join Path that the persistence layer will
know how to join the SQL tables to each other.
•
For each data query, a mapping from the returned attribute name to the data type of the
attribute is required. This allows the code whether an INTEGER SQL type should be an
INTEGER data type or actually a BigDecimal data type.
All of the metadata is required so that the persistence layer can successfully generate a data
model as well as all of the events to manipuate the object.
2.3. Where can I find example PDL (Persistence Definition Language) files that define object
types?
At the top level of any project you will find a pdl directory. In there, you will find many PDL
files that should provide plenty of examples.
2.4. Where do I put my PDL files?
PDL files should be kept in a directory at the same level as the SQL and src files. If the
PDL does not contain any database specific queries (e.g., something containing a connect
by statement) then it should end in (.pdl). Otherwise, you should create a copy of the query
for each database and name each copy appropriately: .ora.pdl for Oracle or .pg.pdl for
PostgreSQL.
2.5. I want to create a new object type that extends ACSObject. What do I do?
When you extend an object type, the new object type will inherit all the properties (attributes
and role references) of the super type. A child object type can override the parent’s attributes
(but not role references), as long as the new attribute does not violate any constraints placed
on the supertype’s attribute. For example, suppose that the parties object type defines an email
attribute that is required. That is, parties.email has multiplicity of 1..1. You can create a persons
object type that extends parties. You cannot make the email address optional in the persons
object type because it is already required by the supertype.
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Suppose you are defining an object type named &quot;ChewingGum&quot; that extends ACSObject. To
specify that an object type extends another, do the following:
•
Before defining your object type but after declaring your model, make sure to import the
ACSObject type.
•
When defining your object type, specify that the supertype of the &quot;Chewing Gum&quot; object
type is &quot;ACSObject&quot; and import the namespace for ACSObject. In the PDL file, you currently write:
import com.arsdigita.kernel.*;
object type ChewingGum extends ACSObject {
--}
•
When you define your table in the database, make the primary key reference the
acs_objects table. This is only required, however, when you manually specify your
SQL. In most cases, defining the PDL will be enough to get your started (you must,
however, still load the auto-generated table). The following shows how to manually define
the table.
create table acs_objects (
object_id
integer primary key
);
create table chewing_gum (
gum_id
integer primary key
references acs_objects(object_id)
);
•
When you create your Java class, you can extend the ACSObject class in the
com.arsdigita.kernel package.
See Section 9.2.6 Object Type Inheritance for a longer example.
2.6. What is a DataQuery and how do I use it?
A DataQuery encapsulates SQL queries. You can retrieve a DataQuery by name from the
PDL file, set filters on its attributes, execute the event, iterate over the result set, and access the
attribute values.
Underneath, the actual SQL query and data model used are hidden from application code.
For more information, see the documentation on Section 9.4 Named SQL Events.
2.7. How do I specify a custom SQL query?
You can create a DataQuery by specifying a SQL query and as many attribute/column mappings as you like. You can then define bind variables or set filters on that query to gain the
final query you wish.
2.8. What is an Object/Reference Key and why do I need one?
The object key (Object Key) declared in the PDL files is used by the persistence system
to uniquely identify a particular object in the database. For instance, the object key for
acs_object is &quot;id&quot;, which is the name of the attribute that maps to the object_id column
in the acs_objects table.
Object keys can contain singule values or they can be compound (they can be specified using
1 to N attributes). For more information, see Section 9.2.3.3 Object Key.
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2.9. How do I retrieve a DataQuery, DataCollection, or DataAssociation in the order
I want (e.g., there is a sort_order link attribute that I want to sort by)?
To do this, use the setOrder() method. For further information, see Section 9.5.2 Ordering.
2.10. What is the OID class used for?
The OID class encapsulates the details of the primary key of an object. You use instances of
OID for retrieving an object from the database and you set the OID to a known value. You can
also get an OID object from a DataObject.
2.11. I would like to retrieve all instances of a particular object type (e.g.,
com.arsdigita.kernel.User). How do I do this?
You will want to use the method in the class com.arsdigita.persistence.Session
(http://rhea.redhat.com/doc/waf/6.0/api/com/arsdigita/persistence/Session.html) that retrieves
a DataCollection for all instances of a data object type. The DataCollection can be
filtered to narrow the results. It is possible to request individual properties of the collection
without instantiating an object. You can also instantiate the data object, and if you use the
DomainObjectFactory, you can get a DomainObject from the data object. It is recommended, however, that you do not instantiate the object unless absolutely necessary, because
creating the object consumes extra memory resources as compared to iterating through the
DomainCollection.
As a specific example, to get all users in the system, you can execute the following line:
DataCollection authors =
SessionManager.getSession().retrieve(&quot;com.arsdigita.kernel.User&quot;);
For more information, see Section 9.2.5 Creating and Retrieving Objects in Java.
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Chapter 10.
Kernel Tutorial
This chapter discusses how to use permissioning and domain objects, answers frequently-asked questions about the WAF security mechanisms and API, and touches on extending the authentication
system. Please refer to Chapter 3 WAF Component: Kernel for more information about the concepts
used in these tutorials.
10.1. Permissions Tutorial
10.1.1. Granting Access
Granting access to a party is accomplished by creating a PermissionDescriptor and passing it to
PermissionService.grantPermission. The following example grants read privilege on MyACSObject 50 to Group 5:
import
import
import
import
com.arsdigita.kernel.permissions.PermissionService;
com.arsdigita.kernel.permissions.PermissionDescriptor;
com.arsdigita.kernel.permissions.PrivilegeDescriptor;
com.arsdigita.persistence.OID;
OID acsObject = new OID(&quot;example.MyACSObject&quot;,
new BigDecimal(50));
OID party = new OID(&quot;com.arsdigita.kernel.Group&quot;, new BigDecimal(5));
PermissionDescriptor perm =
new PermissionDescriptor(PrivilegeDescriptor.READ,
acsObject, party);
PermissionService.grantPermission(perm);
The next example grants admin privilege on all objects to User 100:
import
import
import
import
com.arsdigita.kernel.permissions.PermissionService;
com.arsdigita.kernel.permissions.UniversalPermissionDescriptor;
com.arsdigita.kernel.permissions.PrivilegeDescriptor;
com.arsdigita.persistence.OID;
OID party = new OID(&quot;com.arsdigita.kernel.User&quot;, new BigDecimal(100));
PermissionDescriptor perm =
new UniversalPermissionDescriptor(PrivilegeDescriptor.ADMIN,
party);
PermissionService.grantPermission(perm);
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10.1.2. Revoking Access
Revoking a privilege on an object from a party is accomplished by creating a PermissionDescriptor and passing it to PermissionService.revokePermission. The following example revokes
read privilege on MyACSObject 50 from Group 5:
import
import
import
import
com.arsdigita.kernel.permissions.PermissionService;
com.arsdigita.kernel.permissions.PermissionDescriptor;
com.arsdigita.kernel.permissions.PrivilegeDescriptor;
com.arsdigita.persistence.OID;
OID acsObject = new OID(&quot;example.MyACSObject&quot;,
new BigDecimal(50));
OID party = new OID(&quot;com.arsdigita.kernel.Group&quot;, new BigDecimal(5));
PermissionDescriptor perm =
new PermissionDescriptor(PrivilegeDescriptor.READ,
acsObject, party);
PermissionService.revokePermission(perm);
The next example revokes admin privilege on all objects from User 100:
import
import
import
import
com.arsdigita.kernel.permissions.PermissionService;
com.arsdigita.kernel.permissions.UniversalPermissionDescriptor;
com.arsdigita.kernel.permissions.PrivilegeDescriptor;
com.arsdigita.persistence.OID;
OID party = new OID(&quot;com.arsdigita.kernel.User&quot;, new BigDecimal(100));
PermissionDescriptor perm =
new UniversalPermissionDescriptor(PrivilegeDescriptor.ADMIN,
party);
PermissionService.revokePermission(perm);
10.1.3. Basic Access Check
The basic access check indicate whether a user has a privilege on an object. User X has privilege Y
on object Z if either of the following is true:
•
Privilege Y or admin has been granted universally to user X or some group to which X belongs.
•
Privilege Y or admin has been granted on object Z or some object from which Z inherits permissions (via Z’s context) to user X or some group to which X belongs.
To perform this check, you create a PermissionDescriptor and pass it to PermissionService.checkPermission. The following example checks read privilege on MyACSObject 50 for
User 100:
import
import
import
import
com.arsdigita.kernel.permissions.PermissionService;
com.arsdigita.kernel.permissions.PermissionDescriptor;
com.arsdigita.kernel.permissions.PrivilegeDescriptor;
com.arsdigita.persistence.OID;
OID acsObject = new OID(&quot;example.MyACSObject&quot;,
new BigDecimal(50));
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105
OID party = new OID(&quot;com.arsdigita.kernel.User&quot;, new BigDecimal(100));
PermissionDescriptor perm =
new PermissionDescriptor(PrivilegeDescriptor.READ,
acsObject, party);
if (PermissionService.checkPermission(perm)) {
// user 100 has read access on object 50
} else {
// user 100 does NOT have read access on object 50.
// You might handle this case by displaying an
// &quot;access forbidden&quot; message.
}
As the previous examples have shown, operations performed on PermissionDescriptor can also
be performed on UniversalPermissionDescriptor when dealing with universal access control
(that is, access to all objects). The same applies for PermissionService.checkPermission().
The following example checks whether user 100 has admin privilege universally:
import
import
import
import
com.arsdigita.kernel.permissions.PermissionService;
com.arsdigita.kernel.permissions.UniversalPermissionDescriptor;
com.arsdigita.kernel.permissions.PrivilegeDescriptor;
com.arsdigita.persistence.OID;
OID party = new OID(&quot;com.arsdigita.kernel.User&quot;, new BigDecimal(100));
PermissionDescriptor perm =
new PermissionDescriptor(PrivilegeDescriptor.ADMIN,
party);
if (PermissionService.checkPermission(perm)) {
// user 100 has admin access universally (that is, on all objects).
} else {
// user 100 does not universal admin access universally.
// You might handle this case by displaying an
// &quot;access forbidden&quot; message.
}
10.1.4. Allowed Targets Check
The allowed targets check is performed on a DomainCollection or DataCollection in order to
filter the result set of domain/data objects to only those on which a given user has a given privilege.
The rules for determining whether a given user has a given privilege on an object are described in
Section 10.1.3 Basic Access Check.
You
can
be
perform
this
filtering
by
using
either
PermissionService.filterObjects(DomainCollection, PrivilegeDescriptor, Party)
or
PermissionService.filterObjects(DataCollection, PrivilegeDescriptor,
Party). The following example retrieves all MyACSObjects on which User 100 has read
privilege:
import
import
import
import
import
import
com.arsdigita.kernel.permissions.PermissionService;
com.arsdigita.kernel.permissions.PermissionDescriptor;
com.arsdigita.kernel.permissions.PrivilegeDescriptor;
com.arsdigita.persistence.OID;
com.arsdigita.persistence.DataCollection;
com.arsdigita.persistence.SessionManager;
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DataCollection objects = SessionManager.getSession()
.retrieve(&quot;example.MyACSObject&quot;);
OID party = new OID(&quot;com.arsdigita.kernel.User&quot;, new BigDecimal(100));
PermissionService.filterObjects(object, PrivilegeDescriptor.READ, party);
// iterate over filtered results
while (objects.next()) {
...
}
10.1.5. Setting the Access Control Context of an ACSObject
An ACSObject can inherit permissions from another ACSObject, which is called its context. To
set the context of an object, use PermissionService.setContext(object, context). The
context may be set to null to signify that the object should not inherit permissions from any other
object. Note that universal permissions still apply to any object, even if its context is null.
10.1.6. Defining New Privileges
There are 4 pre-defined privileges in the system, similar to file system privileges:
• read
- The privilege to read or view an object.
• write
- The privilege to write or edit an object.
• create - The privilege
to create new objects within an object. For example, a user who has create
privilege on a given directory is allowed to create new files within the directory.
• admin
- Implies all other privileges.
Application developers may cautiously define new privileges to represent specific actions in the
context of an application. For example, a content management system may support publishing a
content item that is in final draft, but this operation should be restricted to certain parties for each
content item. To accomplish this, the content management application creates a publish privilege
from its initializer, as illustrated by the following code fragment.
if (PrivilegeDescriptor.get(&quot;publish&quot;) == null) {
PrivilegeDescriptor.createPrivilege(&quot;publish&quot;); }
10.2. Domain Objects Tutorial
10.2.1. Building the Domain Object
This section will take you step by step through the process of building a domain object.
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10.2.1.1. Starting the Class
A domain object starts off as a standard Java class that extends one of the four domain object base
classes. Because of the auditing and permissioning requirements, AuditedACSObject is the base
class.
The code in Example 10-1 illustrates the initial definition of the class and the import statements.
package com.arsdigita.notes;
import
import
import
import
import
import
import
import
import
import
com.arsdigita.db.Sequences;
com.arsdigita.domain.DataObjectNotFoundException;
com.arsdigita.auditing.AuditedACSObject;
com.arsdigita.kernel.Stylesheet;
com.arsdigita.kernel.User;
com.arsdigita.persistence.DataAssociation;
com.arsdigita.persistence.DataObject;
com.arsdigita.persistence.PersistenceException;
com.arsdigita.persistence.OID;
com.arsdigita.persistence.metadata.ObjectType;
(1)
import java.math.BigDecimal;
import java.sql.SQLException;
import java.util.Date;
// Stylesheets
import java.util.Locale;
import java.util.ArrayList;
import org.apache.log4j.Category;
/**
* Note class. Extends AuditedACSObject to implement
(2)
* persistent Note objects.
*
* p
* Note: according to current DomainObject docs, APIs are not yet
* stable. Changes may invalidate the Note class.
*
* @author Scott Seago
**/
public class Note extends AuditedACSObject {
(3)
private static Category log =
Category.getInstance(Note.class.getName());
(2)
/**
* BASE_DATA_OBJECT_TYPE represents the full objectType name for the
* Note class
**/
private static final String BASE_DATA_OBJECT_TYPE =
(4)
&quot;com.arsdigita.notes.Note&quot;;
...
/**
* Returns the appropriate object type for a Note so that proper
* type validation will occur when retrieving Notes by OID
*
* @return The fully qualified name of of the base data object
* type for the Note object type.
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*/
protected String getBaseDataObjectType() {
return BASE_DATA_OBJECT_TYPE;
}
(4)
}
(1)
The AuditedACSObject is imported from the auditing service package.
(2)
Log4j is used as a uniform debugging tool across WAF. The convention for initializing the log4j
system is to initialize a category with the name of the current class, as shown here.
(3)
By extending this baseclass, this Java class becomes a domain object. It inherits a data object
and methods for manipulating it. Calls to these methods are automatically observed and modifications are logged in the audit trail.
(4)
The data object type for the domain object is declared as a member variable,
BASE_DATA_OBJECT_TYPE. It is final and static, so the compiler will replace it with a constant.
An inherited function, getBaseDataObjectType, is overridden to return this variable. This
method is used by the constructors on the superclasses to verify that the data object matches
this type or is a subtype. For more information on this topic, see Section 10.2.1.2 Constructors.
Example 10-1. Starting to Build the Domain Object
10.2.1.2. Constructors
Before any of the methods of a class can be used, an instance must be constructed in memory. There
are several different varieties of constructors for domain objects, all of which are illustrated in the
Notes domain object.
There are two different types of constructors for domain objects. One is used for constructing domain
objects by creating a new data object. The no-arg constructors — the String typename and the
ObjectType type — are this type of constructor. These constructors use the persistence system to
create a new data object that matches the type passed as an argument.
The other type of constructor relies on retrieval of an existing data object to construct the domain
object. The first of these takes an Object ID or OID as input, and then retrieves a data object corresponding to that OID. An OID is comprised of two pieces: a BigDecimal numeric ID and an object
type identifier. The second constructor takes a data object as input and constructs a DomainObject
to wrap it. This constructor does not need to construct the underlying data object, so it is preferable to
use this constructor if the data object has already been loaded into memory.
These constructors exist in DomainObject, ObservableDomainObject, ACSObject, and AuditedACSObject. Subclasses should replicate these constructors, unless there is a good reason to
restrict them. The comments following Example 10-2 explain the overall utility of each constructor,
and why each subclass should use them. Additional constructors can be added, and this is encouraged
if it makes the class more convenient to use.
Note
Be aware that none of the constructors will change the persistent state of the DomainObject or its
data object. To store a domain object’s properties in the database, the save method must be called.
To delete a DomainObject, the delete method must be called.
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public class Note extends AuditedACSObject {
/**
* BASE_DATA_OBJECT_TYPE represents the full objectType name for the
* Note class
**/
private static final String BASE_DATA_OBJECT_TYPE =
&quot;com.arsdigita.notes.Note&quot;;
/**
* Default constructor. The contained DataObject is
* initialized with a new DataObject with an
* ObjectType of &quot;Note&quot;.
*
* @see AuditedACSObject#AuditedACSObject(String)
* @see com.arsdigita.persistence.DataObject
* @see com.arsdigita.persistence.metadata.ObjectType
**/
public Note() {
this(BASE_DATA_OBJECT_TYPE);
}
/**
* Constructor. The contained DataObject is
* initialized with a new DataObject with an
* ObjectType specified by the string
* typeName
*
* @param typeName The name of the ObjectType of the
* contained DataObject.
*
* @see AuditedACSObject#AuditedACSObject(ObjectType)
* @see com.arsdigita.persistence.DataObject
* @see com.arsdigita.persistence.metadata.ObjectType
**/
public Note(String typeName) {
super(typeName);
}
/**
* Constructor. The contained DataObject is
* initialized with a new DataObject with an
* ObjectType specified by type
*
* @param type The ObjectType of the contained
* DataObject.
*
* @see AuditedACSObject#AuditedACSObject(ObjectType)
* @see com.arsdigita.persistence.DataObject
* @see com.arsdigita.persistence.metadata.ObjectType
**/
public Note(ObjectType type) {
super(type);
}
(1)
(2)
(3)
/**
* Constructor. Retrieves a Note instance, retrieving an existing
* note from the database with OID oid. Throws an exception if an
* object with OID oid does not exist or the object
* is not of type Note
*
* @param oid The OID for the retrieved
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* DataObject.
*
* @see AuditedACSObject#AuditedACSObject(OID)
* @see com.arsdigita.persistence.DataObject
* @see com.arsdigita.persistence.OID
*
* @exception DataObjectNotFoundException Thrown if we cannot
* retrieve a data object for the specified OID
*
**/
(4)
public Note(OID oid) throws DataObjectNotFoundException {
super(oid);
}
...
}
(1)
The empty constructor is used to construct a new Note with its default data object type. This is
the common case for constructing a new Note, where a specific subtype of domain object is not
needed and an existing Note is not being retrieved.
(2)
The typeName specified in this constructor must be a String that names an object type. This
does the same thing as the constructor that takes an object type, but is more convenient, because
you only need to specify a String with the type name.
(3)
This constructor takes an ObjectType that matches the base object type, in this case,
com.arsdigita.notes.Note or a subtype. The constructor requiring an ObjectType can
be used to specify a specific subtype of the Notes data object. This is useful if the data object
may be used with different domain objects that have different methods.
In most cases, the empty constructor, which defaults to the base object type, is sufficient, and
any reason to use the other constructors should be specified. Even if the Note domain object will
not be used with multiple object types, it is necessary to have these constructors for a subclass to
provide this functionality. Without providing the constructors on every class, a subclass cannot
rely on the constructor chain to reach the constructors on ACSObject and DomainObject.
(4)
This constructor is used to construct a Notes domain object with a Notes domain object that
has already been created. The OID is used to retrieve an instance of the correct domain object.
The retrieved data object can then be accessed using the set/get methods and all other methods
defined.
Example 10-2. Domain Object Constructors
The role of each constructor can be clarified by examining how the constructors are implemented in
DomainObject, the root base class for all domain objects.
public abstract class DomainObject {
private final DataObject m_dataObject;
/**
* Constructor. The contained DataObject is
* initialized with a new DataObject with an
* ObjectType specified by the string
* typeName.
*
* @param typeName The name of the ObjectType of the
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* new instance.
*
* @see com.arsdigita.persistence.Session#create(String)
* @see com.arsdigita.persistence.DataObject
* @see com.arsdigita.persistence.metadata.ObjectType
**/
public DomainObject(String typeName) {
Session s = SessionManager.getSession();
(1)
if (s == null) {
throw new RuntimeException(&quot;Could not retrieve a session
from &quot; + &quot;the session manager while instantiating &quot; +
&quot;a class with ObjectType = &quot; + typeName);
}
m_dataObject = s.create(typeName);
initialize();
}
/**
* Constructor. The contained DataObject is
* initialized with a new DataObject with an
* ObjectType specified by type.
*
* @param type The ObjectType of the new instance.
*
* @see com.arsdigita.persistence.Session#create(ObjectType)
* @see com.arsdigita.persistence.DataObject
* @see com.arsdigita.persistence.metadata.ObjectType
**/
public DomainObject(ObjectType type) {
Session s = SessionManager.getSession();
(1)
if (s == null) {
throw new RuntimeException(&quot;Could not retrieve a session
from &quot; + &quot;the session manager while instantiating &quot; +
&quot;a class with ObjectType = &quot; + type.getName());
}
m_dataObject = s.create(type);
initialize();
}
/**
* Constructor. The contained DataObject is retrieved
* from the persistent storage mechanism with an OID specified by
* oid.
*
* @param oid The OID for the retrieved
* DataObject.
*
* @exception DataObjectNotFoundException Thrown if we cannot
* retrieve a data object for the specified OID
*
* @see com.arsdigita.persistence.Session#retrieve(OID)
* @see com.arsdigita.persistence.DataObject
* @see com.arsdigita.persistence.OID
**/
public DomainObject(OID oid) throws DataObjectNotFoundException {
Session s = SessionManager.getSession();
if (s == null) {
throw new RuntimeException(&quot;Could not retrieve a session (2)
from &quot; + &quot;the session manager while instantiating &quot; +
&quot;a class with OID = &quot; + oid.toString());
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}
m_dataObject = s.retrieve(oid);
if (m_dataObject == null) {
throw new DataObjectNotFoundException
(&quot;Could not retrieve a DataObject with &quot; +
&quot;OID = &quot; + oid.toString());
}
initialize();
}
/**
* Constructor. Creates a new DomainObject instance to encapsulate
* a given data object.
*
* @param dataObject The data object to encapsulate in the new domain
* object.
* @see com.arsdigita.persistence.Session#retrieve(String)
**/
public DomainObject(DataObject dataObject) {
m_dataObject = dataObject;
initialize();
}
(2)
/**
* Returns the base data object type for this domain object class.
* Intended to be overridden by subclasses whenever the subclass will
* only work if their primary data object is of a certain base type.
*
* @return The fully qualified name (&quot;modelName.typeName&quot;) of the base
* data object type for this domain object class,
* or null if there is no restriction on the data object type for
* the primary data object encapsulated by this class.
**/
protected String getBaseDataObjectType() {
return null;
}
/**
* Called from all of the DomainObject constructors
* to initialize or validate the new domain object or its
* encapsulated data object. This was introduced in order to
* support efficient validation of the encapsulated data object’s
* type. If the validation is typically performed in class
* constructors, then redundant validation is performed in
* superclass constructors. This validation now occurs here.
**/
protected void initialize() {
if (m_dataObject == null) {
throw new RuntimeException
(&quot;Cannot create a DomainObject with
(3)
a null data object&quot;);
}
String baseTypeName = getBaseDataObjectType();
if (baseTypeName == null) {
return;
}
// ensure data object is instance of baseTypeName
// or a subtype thereof.
ObjectType.verifySubtype(baseTypeName,
m_dataObject.getObjectType());
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}
...
}
(1)
These constructors are used to create an empty data object. The Session class is used look up
the metadata that defines the object type and returns the data object. Because the data object is a
private member variable, it is denoted m_dataObject.
(2)
These two constructors are used to create a DomainObject when a data object already exists.
The OID-based constructor searches for a data object with the given OID. If the object cannot
be found, a DataObjectNotFound exception is thrown. Otherwise, the DomainObject is initialized with the given data object. The data-object-based constructor is used if the data object is
available, so that an additional one does not need to be retrieved from the database.
(3)
The initialize() is called after the domain object instance is created. One use of this function
is to validate the data object type to see if it is the same type or a subtype of the base data object
type. If not, an exception is thrown. In order for this to work, your subclass must implement
getBaseDataObjectType(), as in the Notes example. Subclasses of DomainObject can add
their own initialization logic, but should always call super.initialize() in the first line of
the function so that initializations from the superclasses are processed.
Example 10-3. Implementing Constructors
10.2.1.3. Adding Create Methods
The constructors described in Section 10.2.1.2 Constructors are intended to be used for creating empty
data objects or retrieving existing data objects. However, in some situations, it is useful to have a
method that takes in a set of application-specific parameters and creates a domain object for you:
/**
* Creates a new note and sets the title, body, and theme.
*
* @param title The title describing the note.
* @param body The body of the note.
* @param theme The theme of the note.
*/
public static Note create(String title, String body, NoteTheme theme) {
Note note = new Note();
note.setTitle(title);
note.setBody(body);
note.setTheme(theme);
return note;
}
This method is static, so it can be called without an instance of a Note. It constructs a new note and
then sets the title, body, and theme properties to the values passed into the method. It then returns the
constructed Note object. The Note’s data is not saved in the database by the constructor. Such data is
not persisted until the save method is executed.
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10.2.1.4. DomainObject Methods
Several methods are inherited from DomainObject that are useful for building other methods for
subclasses. In general, methods are added to subclasses to provide application logic specific to a
business domain. A common case of this are accessors and mutators for data object properties. Such
methods are usually called by process objects or UI components.
10.2.1.4.1. Accessors and Mutators
Because DomainObjects wrap data objects, accessors and mutators for the domain object properties
are common methods to provide on a domain object. The DomainObject class provides a set and
get that are automatically delegated to the data object member of DomainObject. The set method
is used to set properties of the domain object to a value. The get method is used to retrieve the values
of those properties.
Using the Note domain object, the following example demonstrates how to implement an accessor
and mutator for the contained data object’s property.
/**
* Retrieve the title of the note.
*
* @return The title.
*/
public String getTitle() {
return (String) get(&quot;title&quot;);
}
/**
* Set the title of the note.
*
* @param title A title for the note.
*/
public void setTitle(String title) {
set(&quot;title&quot;, title);
}
The accessor, getTitle works by calling get with the name of the property to retrieve. The
getmethod returns a java.lang.Object, so the return type must be casted to a String. The
setTitle method works by calling the set with the name of the property to be set and the value.
The member data object in DomainObject is private to prevent access to the data object outside of the
methods, ensuring an interface/implementation barrier. Subclasses of DomainObject cannot access
the data object directly but must use methods on DomainObject instead. Because this barrier guarantees that all access to the properties of the data object are through set and get methods, subclasses
can add behavior to these methods. For example, the ObservableDomainObject adds behavior
to the set method that enables observers of the DomainObject to be notified when a property is
changed.
10.2.1.4.2. Initialize
The DomainObject class provides an initialize method that is executed after the constructor is run.
The Domain Subclasses can override this method and add further initialization logic. However, the
initialize method on the superclass should be run to ensure that all inherited member variables
are initialized and so that the data object type checking is executed.
A good use of the initialize method is to set initial values for data object properties. The ACSObject class uses the initialize method to determine the value for the ObjectType property.
/**
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* Called from base class constructors (DomainObject constructors).
*/
protected void initialize() {
super.initialize();
if (isNew()) {
String typeName =
getObjectType().getModel().getName() +
&quot;.&quot; + getObjectType().getName();
set(&quot;objectType&quot;, typeName);
}
}
10.2.2. Conventions
1. Every domain object with a public constructor should have a public final static String
BASE_DATA_OBJECT_TYPE variable with the value equal to the primary data object type used
by the domain object. The common use for the BASE_DATA_OBJECT_TYPE variable is to construct an OID for the data object given its numeric id. For convenience, you can provide a no-arg
constructor that will dispatch to the object type constructor with the BASE_DATA_OBJECT_TYPE
variable.
2. The protected method getBaseDataObjectType is required to provide proper data object
type checking. In the common case, the method returns the BASE_DATA_OBJECT_TYPE variable. The DomainObject initialize method ensures that the data object used to create a
DomainObject is equal to that type or a subtype of the object type returned by this method.
For example, if you try to instantiate an ACSObject with a data object that is not a subtype of
the ACSObject data object type, you will get an exception. By default, this method returns null,
which disables the type checking
10.2.3. Examples
10.2.3.1. Creating Messages
By default, a new Message has a MIME type of text/plain, so creating and storing simple text
messages is straightforward:
Party from; Message msg = new Message(from, &quot;the subject&quot;, &quot;the body&quot;);
msg.save();
To create a message in a different format, like text/html, the API provides a method to set the
MIME type when the Message is created:
Message msg = new Message(from, subject);
msg.setBody(&quot; p this is the body /p &quot;, MessageType.TEXT_HTML);
msg.save();
Finally, a Message can also be instantiated by retrieving it from the database by supplying its unique
ID:
Message msg = new Message(new BigDecimal(1234));
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Note that the Message class only support bodies with a primary MIME type of text. The MessageType interface defines legal MIME types for use in specifying a message body.
10.2.3.2. Referring to Other Objects
Messages can store an optional reference to an ACSObject. This is useful for attaching messages
to other items in the system. For example, a discussion forum might implement a Topic class to
represent a collection of related messages. The process of adding a message to a given topic can be
implemented by setting a reference to that topic:
// One topic in a discussion forum
class Topic extends ACSObject {
// Add a new posting for this topic
addNewPosting (User postedBy, String subject, String post) {
Message msg = new Message(postedBy, subject, post);
msg.setRefersTo(this);
msg.save();
}
}
10.2.3.3. Attachments
Additional pieces of content can be attached to a message. These content items can be any media
type with a supported DataHandler. Convenience methods are provided for attaching plain text
documents directly to a message:
Message msg = new Message(from, subject);
msg.setText(&quot;See the attached document.&quot;);
msg.attach(&quot;A simple document&quot;, &quot;simple.txt&quot;);
msg.save();
To attach more complex types of content, you use a MessagePart and an appropriate data source
or DataHandler. There are convenience methods to attach content retrieved from a File or a URL.
The following example shows how to attach an uploaded image to a message:
File file = new File(&quot;image.gif&quot;);
MessagePart part = new MessagePart();
part.setContent(image, &quot;image.gif&quot;, &quot;An image&quot;);
Message msg = new Message(from, subject, &quot;See attached image&quot;);
msg.attach(part);
msg.save();
The code for downloading the image from a remote server is almost identical:
URL url = new URL(&quot;http://mysite.net/image.gif&quot;);
MessagePart part = new MessagePart();
part.setContent(url, &quot;image.gif&quot;, &quot;An image from mysite&quot;);
Message msg = new Message(from, subject, &quot;See attached image&quot;);
msg.attach(part);
msg.save();
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Note that the above two examples do not explicitly set a MIME type for the content. This is determined
automatically when the content is handed off to a DataHandler for processing. In both cases shown
above the content will be of type image/gif.
10.2.3.4. Simple Threading
A Message object can store a reference to another Message object to implement basic threading. A
reply is created using the reply() method of the parent Message:
Message parent = new Message(new BigDecimal(1234)); Message reply =
parent.reply();
reply.setFrom(from);
reply.setText(&quot;I do not agree, because...&quot;);
reply.save();
When a reply is created this way, the subject is initialized as appropriate for a reply to the parent, and a
reference to the parent message is stored internally. The client code must set other message properties,
including the body of the reply.
10.2.3.5. Advanced Threading
Many applications need to store a more complex, structured set of responses than the flat organization
provided by Message. The ThreadedMessage class provides support for organizing messages into
a tree structure as outlined above. The API for ThreadedMessage is identical, but the reply() also
takes care of setting a special sort key that determines the proper location of a message in the tree.
The following example shows a simple discussion thread and the technique used to retrieve all messages from the database for display in the correct order. The structure of the underlying tree is as
follows:
msg0
msg2
msg4
msg5
msg3
msg6
msg1
Although in a real application the structure of messages and replies would be generated over time, the
following example shows the sequence of calls that produces the same organization, for illustration
purposes.
//
//
//
//
A common object that all messages refer to.
In practice this might a forum or a content
item that is being discussed by a group of
collaborators.
ACSObject anchor;
// Create the message
ThreadedMessage msg[];
msg[0] = new ThreadedMessage();
msg[0].setRefersTo(anchor);
msg[1] = new ThreadedMessage();
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msg[1].setRefersTo(anchor);
msg[2]
msg[3]
msg[4]
msg[5]
msg[6]
=
=
=
=
=
msg[0].replyTo(from,body);
msg[0].replyTo(from,body);
msg[2].replyTo(from,body);
msg[2].replyTo(from,body);
msg[3].replyTo(from,body);
Note that the two root-level messages (0 and 1) explicitly set the reference to our anchor object, but
the replies do not. This information is automatically transferred to the replies when they are created,
as are the subject and other properties, in the same way as Message.reply().
In addition, ThreadedMessage.replyTo() also sets a special sort key that determines the correct
position of the message in the tree. Details of the sort keys are not important, but they are generated
so that all common messages can be retrieved in the correct order using a single order by clause.
A special query provided by the messaging package is used to reconstruct the tree structure shown
above:
Session session = SessionManager.getSession();
DataQuery query = session.retrieveQuery
(&quot;com.arsdigita.messaging.getMessageTree&quot;);
query.addEqualsFilter(&quot;object&quot;, anchor);
while (query.next() {
ThreadedMessage msg = new ThreadedMessage
((BigDecimal) query.get(&quot;id&quot;));
System.out.println(&quot;message &quot; + msg.toString());
}
The addEqualsFilter is required to retrieve only those messages that refer to the same ACSObject.
10.3. Security Service FAQ
This section addresses common questions developers have when implementing a security service
through the kernel.
1. How do I determine whether the user is logged in?
KernelHelper.getKernelRequestContext(request).getUserContext().isLoggedIn()
returns true if the user is logged in, false otherwise.
2. How do I get the ID for the current user?
KernelHelper.getKernelRequestContext(request).getUserContext().getUserID()
returns the current user’s ID. This method throws an exception if the user is not logged in, so check
with isLoggedIn() first. If the calling code needs a User object for the current user, it should call
getUser() instead.
3. How do I get the User object for the current user?
KernelHelper.getKernelRequestContext(request).getUserContext().getUser() returns a User object for the current user. This method throws an exception if the user is not logged in,
so check with isLoggedIn() first. This method throws DataObjectNotFoundException if the user
doesn’t exist; calling code should catch this exception and handle it appropriately. The User object
provided by this method is cached for the current thread, so multiple calls to getUser() incur at most
one database hit.
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KernelHelper.getCurrentUser(request) is a convenience method that returns the current
User object if available, returns null if the user is not logged in, or throws a RuntimeException if the
user is logged in but does not exist.
4. How can a user be logged in but not exist in the database?
WAF logs in users automatically using cookies (or other mechanisms), so it is possible for a client to
present a valid cookie for a user that doesn’t exist. This might happen if the user is deleted, the database
is cleared, or an attacker spoofs a non-existent user’s cookie. WAF uses cryptographic mechanisms to
make the last case unlikely.
5. How do I require that a user is logged in for a given page?
com.arsdigita.ui.login.UserAuthenticationListener is a RequestListener that re-
quires that the user is logged in and that the user exists. This listener should be added to any Bebop
Page that requires login using Page.addRequestListener().
If the user is not logged in or doesn’t exist, the client is redirected to the login page with return_url set
to the original request URL. This ensures that the client will return to the original page after logging
in.
If the user is logged in, this listener provides the methods isLoggedIn() and getUser(). Note that
these methods differ from those in UserContext since they also ensure that the user exists.
6. How do I require that a user is securely authenticated (using SSL or similar) for a given page?
This is
plished
not yet provided in a single API, but
using
a
UserAuthenticationListener
this
and
can be
then
accomcalling
com.arsdigita.kernel.Initializer.getSecurityHelper.isSecure(request) to check
whether the current request is secure.
Note
In the current implementation of WAF, a user must be logged in securely to access a page over SSL.
This restriction will be loosened in the future, and an API for checking secure authentication will be
provided.
7. How do I get the HttpSession object for the current request?
WAF does not currently wrap session retrieval, so request.getSession() will return the current
HttpSession object.
Note
Session management is independent of user authentication, so a session will always exist, whether
or not the user is logged in.
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8. How do I log in a user using a username and password?
KernelHelper.getKernelRequestContext(request).getUserContext().login(username,
password, forever), where forever should be true if the user should be granted a permanent
login cookie, false if the cookie should only last for the current session. For an example, see
com.arsdigita.ui.login.UserRegistrationForm.
Tip
There are several subtle security issues in managing passwords safely, so developers are encouraged to use the provided UI code rather than creating their own. This ensures that developers automatically benefit from fixes in future releases.
9. How do I log in as another user (Administrators only)?
Three methods allow an administrator to assume the role of another user — the &quot;\&quot; is used to break
the lines for printing purposes only::
1. KernelHelper.getKernelRequestContext(request).getUserContext().\
login(username)
2. KernelHelper.getKernelRequestContext(request).getUserContext().\
login(userID)
3. KernelHelper.getKernelRequestContext(request).getUserContext().\
login(User)
The first two versions of this method are convenience wrappers for the third. These methods require
that the current user be an administrator.
After calling any of these methods, the UserContext is updated with the target user’s information;
however, cached user information (such as that provided by UserAuthenticationListener) will
still contain the administrator’s information.
Immediately after calling any of these methods, the client should be redirected to a new page (such as
the user workspace). See com.arsdigita.ui.admin.UserLoginPage for an example.
10. How do I log out a user?
KernelHelper.getKernelRequestContext(request).getUserContext().logout() logs
out the current user. com.arsdigita.ui.login.UserLogoutListener is an ActionListener
that logs out the user by calling this method.
Developers can link to this action listener using an ActionLink. Alternately, developers can link
to a com.arsdigita.ui.login.UserLogoutPage; this page logs out the user and immediately
redirects the client to the registration page.
11. How do I get a user’s email address?
The user’s User object given to the method user.getPrimaryEmail().getEmailAddress()
returns the user’s primary email address as a string. It is possible that getPrimaryEmail() or
getEmailAddress() might return null.
is
a
FormInitListener
that
initializes a form parameter with the current user’s email address, if possible. If the
user is not logged in or has no email address, it leaves the parameter unchanged. See
com.arsdigita.ui.login.UserRegistrationForm for an example.
com.arsdigita.ui.login.EmailInitListener
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12. How do I set a user’s password?
Given the user’s UserAuthentication object, auth.setPassword(password) sets the user’s
password.
Caution
Use the method auth.setPassword(password) carefully, as it can allow an attacker to override the
user’s password.
com.arsdigita.ui.login.PasswordValidationListener
is
a
ParameterValidationListener that checks whether a form parameter value is a strong
password. This listener should always be used before setting the user’s password. See
com.arsdigita.ui.login.ChangePasswordForm for an example.
13. What is / How do I get a user’s UserAuthentication object?
There are four methods for retrieving a user’s UserAuthentication object:
1. UserAuthentication.retrieveForLoginName(String loginName)
2. UserAuthentication.retrieveForUser(OID userOID)
3. UserAuthentication.retrieveForUser(BigDecimal userID)
4. UserAuthentication.retrieveForUser(User user)
The first is appropriate if the username is entered in a form; the last two are appropriate if the user is
already logged in. The UserAuthentication object allows code to check and set a user’s password
and password retrieval question and answer.
Caution
Access to the UserAuthentication object is dangerous, since it can allow an attacker to compromise a user’s account. If at all possible, use the provided UI components and login modules rather
than access this object directly.
14. What is / How do I use the SecurityLogger class?
SecurityLogger wraps the Log4j category called SECURITY. It provides static methods for ap-
pending entries to that log, and automatically inserts the current date and time and, if applicable, the
current client’s IP address.
SecurityLogger is used to log security-relevant events for future auditing. Examples of such events
are bad passwords, malformed cookies, and expired login page accesses. To use the class, simply call
the appropriate class method, such as SecurityLogger.warn().
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10.4. Extending the Authentication System
The main strength of PAM is that the system may be extended with new authentication technologies.
This is done by implementing new LoginModules. For example, an LDAP server can be used to
authenticate a user by username and password. To integrate this behavior into WAF, a new login
module (for example, LDAPLoginModule) must be defined.
LDAPLoginModule would replace LocalLoginModule in the login configuration. It needs its own
configuration information to determine how to connect to the LDAP server. This information can be
hard-coded into the module, read from a file, provided by an Initializer, or passed as an option in
the login configuration.
If the LDAP username does not match the WAF username, another login module must
be defined to map the LDAP username to a WAF user ID. This module, (for example,
LDAPUserLoginModule), would replace UserIDLoginModule and must implement
MappingLoginModule.getUserID(username) appropriately.
Changing the authentication recipe involves editing the sequence of login modules in the login configuration. For example, you can create a variety of authentication sequences in the login configuration
by combining various login modules:
•
Replace certain modules.
•
Change the order of modules.
•
Change the control flag on the modules.
Caution
Not all of the combinations will make sense in terms of authentication practices, and may even be
a security risk. As part of your exploration with authentication, you can read up on the specifics at
http://java.sun.com/security/jaas/apidoc/javax/security/auth/login/Configuration.html.
Chapter 11.
Services Tutorials
These tutorials build upon the discussion in Chapter 4 WAF Component: Services.
11.1. Categorization Tutorial
This section presents an overview of using the categorization layer within WAF. The focus in this
section is on describing the main concepts, classes, and interfaces that a programmer uses to work
with the categorization API.
11.1.1. Overview
This section partially overlaps with and elaborates on the material presented
http://rhea.redhat.com/documentation/api/ccm-core-6.1.0/com/arsdigita/categorization/packagesummary.html.
in
A category is a class of objects or things that share something in common within a conceptual scheme.
It has a short name and an optional description. Each category also has a unique identity. Two distinct
categories may happen to have the same name. They are treated as two different categories, if their
identities are different. This abstraction is represented by the Category class.
There are two kinds of things that can be placed in a category. Firstly, a category may contain other
categories within it. Such categories are called subcategories or child categories. The enclosing category is referred to as the parent category. Category Y is said to be a descendant of category X if either
Y is a child of X, or the parent of Y is a descendant of X. If Y is a descendant of X, then X is called an
ancestor category or ascendant category of X.
Secondly, a category may contain objects other than categories. In our system, a category may contain
any ACSObject. Note that the Category class is itself an ACSObject, but one that has a special
status in the categorization service. If ACSObject A is placed into category X, then we say that A
is a child object of X and X is a parent category of A. We say that object B is a descendant object of
category X, if either B is a child object of X, or the parent category of B is a descendant of X.
Let us first concentrate on the category-subcategory relationship. A category cannot contain two identically named subcategories.
We also require that there be no cycles. In other words, A must not be its own descendant. As an edge
case of this general rule, A cannot contain itself as a subcategory.
A category may have more than one parent. By allowing this, we make possible categorization
schemes that do not look like trees (see below). This complicates matters slightly, insofar as trees
are easier to deal with than the more general structure known as directed acyclic graphs. To restore
the ability to treat categorization schemes as trees, we allow some category-subcategory links to be
marked as &quot;default&quot;. We require that each category have no more than one default parent. A default
parent is also sometimes referred to as a primary parent. Non-default parents are called secondary
parents.
A category with no parents is called a root category. This category and its descendants are referred
to as a category scheme. By disregarding non-default parent-child links, we can obtain a subset of
the categorization scheme that forms a proper rooted tree. The following diagram shows a simple
categorization scheme.
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Figure 11-1. Categorization scheme
In the above diagram, the default parent of Televised Events is TV Shows. Its secondary parent
is Sports. Once we have a categorization scheme, we can start categorizing objects.
The following diagram shows three objects placed in the above categorization scheme.
Figure 11-2. Categorized objects
Note that an object can be categorized under more than one category. In the above example, the movie
The Natural belongs to two categories.
It is possible to have two or more separate categorization schemes within the same application.
Suppose the Legal and Marketing departments each need their own independent categorization
scheme. This is supported through the notion of categorization contexts. Each categorization scheme
is uniquely identified by its root category. Each root category is tied to an application that owns it.
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An application may own more than one category root. Each association may be labeled with a unique
string, called a context.
Figure 11-3. Categorization contexts
In the above example, the application name is Content Section. It has two categorization schemes
identified by the contexts legal and marketing, respectively.
11.1.2. Classes
To use the categorization layer, you should become familiar with the following classes.
com.arsdigita.categorization.Category
http://rhea.redhat.com/documentation/api/ccm-core6.1.0/com/arsdigita/categorization/Category.html
A Category encapsulates a persistent category object. This object contains the name and description for the category, as well as information about whether the category is enabled. It also
provides an API for placing objects within this category, creating subcategories under the instance category, and retrieving parent and child categories and objects.
This class has several notable methods that you should understand before beginning work with
categorization. The URLs have been line broken with a &quot;\&quot; for printing purposes:
• addChild(ACSObject acsObject) is used to create subcategories
egory and to categorize objects within the instance Category.
under the instance Cat-
http://rhea.redhat.com/documentation/api/ccm-core6.1.0/com/arsdigita/categorization/Category.html\
#addChild(com.arsdigita.kernel.ACSObject)
• addRelatedCategory(Category category) is
used to specify a related category, that is,
a category that is not necessarily a parent or a child, but is related in nature.
http://rhea.redhat.com/documentation/api/ccm-core6.1.0/com/arsdigita/categorization/Category.html\ #addRelatedCategory(Category)
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• removeChild(ACSObject object)
is used to delete a mapping with a child.
http://rhea.redhat.com/documentation/api/ccm-core6.1.0/com/arsdigita/categorization/Category.html\
#removeChild(com.arsdigita.kernel.ACSObject)
• getChildren() returns
all subcategories for the given category. See CategoryCollection.
http://rhea.redhat.com/documentation/api/ccm-core6.1.0/com/arsdigita/categorization/Category.html\ #getChildren()
• getObjects() returns
all objects categorized within the instance Category.
http://rhea.redhat.com/documentation/api/ccm-core6.1.0/com/arsdigita/categorization/Category.html\ #getObjects()&quot;
com.arsdigita.categorization.CategoryCollection
A collection of categories, e.g. children of the same parent category.
com.arsdigita.categorization.CategorizedCollection
A collection of (non-category) objects, e.g. child objects of a category.
com.arsdigita.categorization.CategorizedObject
http://rhea.redhat.com/documentation/api/ccm-core6.1.0/com/arsdigita/categorization/CategorizedObject.html
A convenience wrapper for working with the leaf nodes of a category scheme. Methods within
CategorizedObject can be used to retrieve the parent categories or default ancestors of the
object.
Other Classes
These classes work together to provide access to a Bebop Tree that can be used to display the
category tree:
• com.arsdigita.categorization.CategoryTreeModelLite
—
http://rhea.redhat.com/documentation/api/ccm-core6.1.0/com/arsdigita/categorization/CategoryTreeModelLite.html
• com.arsdigita.categorization.CategoryTreeNodeLite
—
http://rhea.redhat.com/documentation/api/ccm-core6.1.0/com/arsdigita/categorization/CategoryTreeNodeLite.html
These classes are not of much importance to you unless you want to change the way the tree
appears. Displaying a category hierarchy is a multiple-step process. First, create a TreeModelBuilder that will instantiate a CategoryTreeModelLite (based either on a query or some
other external data source). This TreeModelBuilder is passed to the Tree, which uses your
builder to create its TreeModel. This process is necessary since a DataObject cannot be used
across connections.
11.2. Categorization Scenarios
11.2.1. Creating a new Category
// Creates the Movies category at the top level with a description
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Category movies = new Category(&quot;Movies&quot;, &quot;long television shows&quot;);
// Create the Romantic Comedies category under the Movies category.
Category romance = new Category(&quot;Romantic Comedies&quot;,
&quot;Comedies with love stories&quot;);
romance.setDefaultParentCategory(movies);
// Create the Titanic category under the Romantic Comedies category.
Category titanic = new Category(&quot;Titanic&quot;, &quot;A category for large movies&quot;);
// set this as the default category
titanic.setDefaultParentCategory(romance);
// Create the Drama category under the Movies category.
Category drama = new Category(&quot;Drama&quot;, &quot;long, not funny stories&quot;);
// Make Drama a parent category (but not the default parent) of Titanic.
drama.addChild(titanic);
// Finally, make movies a parent of Drama
drama.setDefaultParentCategory(movies);
Example 11-1. Creating a new category
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Figure 11-4. Category hierarchy before and after code execution
Adding the &quot;Titanic&quot; category to two categories looks the same as adding it to a single category. The
first category to which an item (category or other ACSObject) is added is explicitly added as the
default category. If a category/item only has one parent, that parent is implicitly the default.
11.2.2. Deleting a Category
// Fetch the Movies category from the database, assuming its id is 123
Category category = new Category(new BigDecimal(123));
// Delete the Movies category.
category.deleteCategoryAndRemap();
Example 11-2. Category deletion
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Figure 11-5. Category hierarchy before and after deleting a category
You can delete a category in the following ways:
•
Deleting Leaf Category — If the category is a leaf, call Category.delete().
•
Remapping Child Categories — If you want to remove the current category and make all
categories that were pointing to it point to its default parent (as in the example), call
Category.deleteCategoryAndRemap().
•
Orphaning Children — If you want to delete the category without remapping any of the child
categories, call Category.deleteCategoryAndOrphan(). Note that there is no way to navigate
from the root to orphaned categories. Effectively, the orphaned categories are no longer part of the
categorization schemes, unless they have non-default parents.
•
Deleting Category Subtree — If you want to delete the entire subtree, including the passed-in
category and all categories below it whose default ancestry can be traced to the root, call Category.deleteCategorySubtree().
11.2.3. Adding more Parent Categories
Category a = new Category(new OID(123));
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Category b = new Category(new OID(124));
Category c = new Category(new OID(125));
if ( a != null &amp;&amp; b != null &amp;&amp; c != null ) {
// Makes Category B the parent of Category A
b.addChild(a);
// Makes Category C the parent of Category A
c.addChild(a);
// Sets Category B as the default parent of Category A
a.setDefaultParentCategory(b);
}
Example 11-3. Adding more parent categories
Figure 11-6. Category hierarchy before and after adding parent categories.
11.2.4. Removing Parent Categories
// Fetch category A from the database.
Category a = new Category(new OID(123));
// Fetch the parent category
Category b = a.getDefaultParentCategory();
b.removeChild(a);
a.setDefaultParentCategory(b.getDefaultParentCategory());
Example 11-4. Removing Parent Categories
Chapter 11. Services Tutorials
Figure 11-7. Category Hierarchy before and after removing parent categories
11.2.5. Retrieving all Subcategories of a given Category
// assume that we have the Category OID (call it categoryOID)
Category category = new Category(categoryOID);
// subcategories is a collection of Category objects
CategoryCollection subcategories = category.getChildren();
Example 11-5. Retrieving Subcategories of a given Category
11.2.6. Retrieving all child objects of a given Category
// assume that we have the Category OID
// (call it categoryOID)
Category category = new Category(categoryOID);
// the Collection will be a Collection of
// CategorizedObjects
Collection childObjects = category.getObjects();
// print out the toString for each object
// and its parents
Iterator childIterator = childObjects.iterator();
while (childIterator.hasNext()) {
CategorizedObject object =
(CategorizedObject) childIterator.next();
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System.out.println(&quot;object = &quot; + object.getObject());
Iterator parents = object.getParentCategories().iterator();
while(parents.hasNext()) {
System.out.println(&quot;parent = &quot; +
((Category) parents.next()).toString());
}
}
Example 11-6. Retrieving child objects of a given Category
11.3. Notification Tutorial
This section deals with several types of notification services you can create in WAF — simple notification, notification with attachment, notification digest, and email alerts.
11.3.1. Creating a Simple Notification
A basic notification requires a sender, a receiver, a subject, and a body. All notifications require a
Message object to send, but in the case of a simple text message, an API allows you to provide the
relevant information and constructs a temporary Message object for you. By default, these notifications will be deleted after they are sent.
The following code fragment depicts the simplest case of sending a notification to a user:
User to
= getRecipient();
User from = getSender();
Notification n = new Notification(to, from, &quot;Subject&quot;, &quot;Body&quot;);
n.save();
This notification will be sent to the user on the next run of SimpleQueueManager. to and from must
be persistent Parties in the database.
You can also create a notification and send it to a Group. When the notification is processed, it will
be sent to each individual User in the Group.
Group group = getTargetGroup();
User from = getSender();
Notification n = new Notification(group, from, &quot;Subject&quot;, &quot;Body&quot;);
n.setExpandGroup(Boolean.TRUE);
n.save();
Note that this option is turned on by default, so the call to setExpandGroup is not strictly necessary.
11.3.2. Creating a Simple Notification with an Attachment
For more complicated notifications, it is better to construct a separate Message object and then wrap
a notification around it for email delivery to a user. The following example shows how to construct
a multipart message with attachments, using both an HTML document fetched from a URL and a
simple text document constructed on the fly.
// Create a message for the body of the notification
User from = getSender();
Message msg = new Message(from, &quot;subject&quot;, &quot;See attachments&quot;);
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// Attach some content fetched from a URL
URL url = new URL(&quot;http://www.yahoo.com/&quot;);
MessagePart part = new MessagePart(&quot;Yahoo&quot;, &quot;Yahoo index page&quot;);
part.setDataHandler(new DataHandler(url));
msg.attach(part);
// Attach a simple text document
msg.attach(&quot;Some additional text&quot;, &quot;file.txt&quot;, &quot;description);
// Save the message
msg.save();
// Send the message to the recipient
User to = getRecipient();
Notification n = new Notification(to, msg);
n.save();
11.3.3. Creating an Hourly Digest
Applications that send frequent notifications to users are often designed to group those messages
into a digest. A common example is a workflow application that sends users a summary of new and
completed tasks every hour.
The notification service supports using an explicit digest. After creating a digest, you can use it to
send future notifications by passing the digest to the notification constructor. All messages sent to a
user through the same digest will be combined into a single outbound message when the digest is next
processed.
// Party responsible for sending the digest
User from = getDigestSender();
String subject = &quot;my-digest&quot;;
String header = &quot;Recent messages&quot;;
String footer = &quot;To unsubscribe, visit
http://mysite.net/unsubscribe&quot;;
Digest digest = new Digest(from, subject,
header, footer);
digest.setFrequency(Digest.HOURLY);
digest.save();
// Create a couple of notifications and send
// them using the hourly digest
Notification n0 = new Notification(digest, user,
from, &quot;Subject0&quot;, &quot;Body0&quot;);
n0.save();
Notification n1 = new Notification(digest, user,
from, &quot;Subject1&quot;, &quot;Body1&quot;);
n1.save();
These two separate notifications will be composed into a single email message and sent to the user
during the next run of the digest queue manager.
Applications typically create their digests when they are installed, and then use them as part of processing alerts for users.
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11.3.4. Email Alerts
The examples above assume that applications will simply need to notify users of some event via email.
However, one of the powerful features of the notification service is that it is built on top of the WAF
messaging service. One of the goals of this design is to make it efficient for messaging applications to
send Message objects directly to users via email, without the need to store any additional information
in the database.
A simple example of this is a bulletin-board (bboard) application that stores each post as a Message,
and then sends each post via email to Users who have subscribed to bboard alerts. In addition to the
basic text of the message, such an application might also need to wrap additional text around it to
include introductory remarks and possibly action links that users can manipulate.
For example, a simple message such as this is my post would typically be sent out with additional information:
Message-ID: 574077721.1185532184.CCMMail@localhost
Date: Fri, 5 Oct 2001 00:43:21 -0700 (PDT)
From: [email protected]
To: [email protected]
Subject: a simple post
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Posted by: Bboard User
Category: Announcement
this is my post
---------This is a posting from the company news bboard.
To reply you can go to:
http://mysite.com/bboard/news/
To unsubscribe from this or other bboard posts go to:
http://mysite.com/bboard/subscriptions/
The notification API includes methods to define the additional text that is wrapped around the contained Message object so that these emails can be generated without creating and storing a duplicate
Message object in the database. In the example above, the header and signature of the notification
would be specified as follows:
Notification notice = new Notification(to,msg);
notice.setHeader
(&quot;Posted by: &quot; + poster.getName() + &quot;\n&quot; +
&quot;Category: &quot; + forum.getCategory());
notice.setSignature
(&quot;---------\n&quot; +
&quot;This is a posting from the company news bboard.\n&quot; +
&quot;To reply you can go to:\n&quot; +
&quot;http://mysite.com/bboard/news/\n&quot; +
&quot;To unsubscribe from this or other bboard posts go to:\n&quot; +
&quot;http://mysite.com/bboard/subscriptions/&quot;);
notice.save();
Applications that use extensive email alerts will probably want to extend Notification so that the
header and signature are set in a special constructor for each notification to be sent out.
For efficiency, applications should avoid sending email alerts to individual users. It is much more
efficient to store the list of recipients in a Group and send a single notification to the group, letting the
notification service expand the group into the list of individual recipients. If you follow this approach,
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an email alert going out to 1000 users will occupy the same amount of space in the database as a single
email.
11.4. Workflow Tutorial
This tutorial covers various tasks that can be accomplished with the workflow service — a simple
workflow, adding a task, rolling back a task, and completing a task.
11.4.1. Simple Workflow
These steps describe the procedure in Procedure 11.1, Creating a Simple Workflow. The procedure
covers creating a hello world workflow and describing the task state change.
1. Design a workflow by defining the desired tasks and the dependencies between them.
2. Create a new named task class for the different task types. Be sure to define the
BASE_DATA_OBJECT_TYPE, the getBaseDataObjectType, constructors, and clone
methods. Also include the methods to invoke.
3. Write the PDL file to support the new task type.
4. Create an instantiator for DomainObjectFactory.
5. Create a workflow template based on the design.
6. Instantiate a workflow from a workflow template.
7. Call the workflow start method to start the Engine.
Creating a Simple Workflow
1. Design your workflow.
2. Create a new task type by subclassing task:
public class HelloWorldTask extends Task {
//The base data object is used for the domain object
public static final String BASE_DATA_OBJECT_TYPE =
&quot;com.arsdigita.workflow.simple.HelloWorldTask&quot;;
protected String getBaseDataObjectType() {
return BASE_DATA_OBJECT_TYPE;
}
//constructors are not inherited from subclasses
//so you’ll need to add them
public HelloWorldTask(String label, String description) {
this(BASE_DATA_OBJECT_TYPE);
initAttributes(label,description);
}
public HelloWorldTask(DataObject taskDataObject) {
super(taskDataObject);
}
public HelloWorldTask() {
this(BASE_DATA_OBJECT_TYPE);
setState(DISABLED);
}
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public HelloWorldTask(OID oid) throws
DataObjectNotFoundException {
super(oid);
}
public HelloWorldTask(BigDecimal id) throws
DataObjectNotFoundException {
this(new OID(BASE_DATA_OBJECT_TYPE, id));
}
protected HelloWorldTask(ObjectType type) {
super(type);
}
protected HelloWorldTask(String typeName) {
super(typeName);
}
// Add functionality in these methods
public void enableEvt() {
System.out.println(getLabel()+&quot;: I am enabled&quot;);
}
public void disableEvt() {
System.out.println(getLabel()+&quot;: I have been disabled&quot;);
}
public void finishEvt() {
System.out.println(getLabel()+&quot;: I am finished&quot;);
}
public void rollbackEvt() {
System.out.println(getLabel()+&quot;:
}
I was rollbacked&quot;);
//Write clone functionality. Note the use of copyAttributes
//
public Object clone() {
HelloWorldTask taskClone = new HelloWorldTask();
copyAttributes(taskClone);
return taskClone;
}
//Add this method because future versions will
protected void copyAttributes(HelloWorldTask taskClone) {
taskClone.setLabel(getLabel());
taskClone.setDescription(getDescription());
taskClone.setActive(isActive());
}
}
Ensure that the constructors, events, and clone methods are coded for the new task type.
3. Write the PDL for the new subclass of task. This is a simple case; you would probably have
additional tables for select and DML statements.
object type HelloWorldTask extends Task {
retrieve {
super;
}
insert
{
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super;
}
update {
super;
}
delete {
super;
}
}
4. In your package initializer section, create and add a new instantiator.
DomainObjectInstantiator instHelloWorldTask =
new ACSObjectInstantiator() {
public DomainObject doNewInstance(DataObject
dataObject) {
return new HelloWorldTask(dataObject);
}
};
DomainObjectFactory.registerInstantiator(
&quot;com.arsdigita.workflow.simple.&quot;,
instHelloWorldTask);
5. Create the workflow template.
public class WFTutorialHello {
public void WFTutorialHello() {
HelloWorldTask helloTask1 =
new HelloWorldTask(&quot;hello 1&quot;, &quot;description&quot;);
HelloWorldTask helloTask2 =
new HelloWorldTask(&quot;hello 2&quot;, &quot;description&quot;);
//Note(1): Save the task before adding the dependency
helloTask1.save();
helloTask2.save();
helloTask2.addDependency(helloTask1);
helloTask2.save();
User user = new User(__USER_ID__)
Workflow wf = new Workflow(&quot;hello example&quot;,
&quot;tutorial example of creating a task&quot;);
wf.addTask(helloTask1);
wf.addTask(helloTask2);
//Note(2): The workflow mad
helloTask1.save();
helloTask2.save();
wf.start();
helloTask1.finish();
helloTask2.finish();
}
}
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11.4.2. Adding a Task to a Workflow
To add a task, you call the addTask method in workflow. The task is inactive when created, and can
be set to be active by calling the setActive(true). A task is not considered part of the workflow
until it becomes active. Tasks are created in an inactive state to allow you to preview them before
altering the workflow state.
Once a task is active, it can affect the workflow and other dependent tasks. Manually setting the task
state is required only when adding a new task to an in-progress workflow. When the workflow is
started, it will automatically set all tasks as active.
11.4.3. Rolling Back a Task
Rolling back a process to a certain task is done by enabling a task early on in the workflow. For
example, to move the process to task A:
//Get reference to task A
taskA.enable();
This will set the workflow back to the state that preceded finishing task A.
11.4.4. Completing a Task
When a task is enabled, call the finish method to complete it:
//Get reference to task A and call finish method
taskA.finish();
11.5. Versioning Tutorial
For a high-level overview and the basic definition of versioning, please refer to Section 4.11 Versioning
Service.
Conceptually, versioning can be divided into two parts:
1. One part concerns PDL syntax that allows the developer to declaratively request certain object
types to be versioned.
2. The other part consists of the Java API provided by the com.arsdigita.versioning package. This API provides classes and methods for interacting with and making use of the versioning service.
This tutorial explains the PDL syntax first, with examples covered in Section 11.5.5 PDL Syntax. If
you wish to skip ahead, you can go directly to Section 11.5.4 Versioning service API.
The implementation and semantics of the versioning service have changed in a number of major ways
after the 5.2 release. If you are familiar with the older implementation and would like a brief summary
of the major differences between the old and current implementations, please refer to Section 11.5.6
Differences between WAF 5.2 and 6.0.
11.5.1. Data-Object-Level Service
The versioning service operates on the data object level. Putting the versioned keyword in front of
the object type definition makes all instances of this type versioned. For example:
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versioned object type Quux {
BigInteger[1..1] id = quuces.id INTEGER;
String[1..1] name
= quuces.name VARCHAR;
object key(id);
}
Example 11-7. The versioned keyword
The consequences of marking an object type as versioned are explained in Section 11.5.2 Fully
versioned types.
11.5.2. Fully versioned types
All instances of the object type Quux defined in Example 11-7 are versioned.
Marking one object type as versioned may impose constraints on other object types, forcing
them to be versioned, too. Two most straightforward examples of this are subtyping and compositecomponent relationship.
object type GreatQuux extends Quux {
String[0..1] email = great_quuces.email VARCHAR;
component Foobar[0..n] foobars = join great_quuces.id
to foobars.great_quux_id;
Country[1..1] country = join great_quuces.country_id
to countries.id;
reference key (great_quuces.id);
}
Example 11-8. Components and required compound attributes
In Example 11-8, the GreatQuux object type is versioned, because it extends a versioned type. If
the object type X is marked as versioned, then the versioning service infers that the subtypes and
components of X are also versioned.
This happens because a data object fully owns its components. As part of properly versioning a data
object, we must version its components. In Example 11-8, this semantic constraint dictates that the
object type Foobar is also versioned.
Generally speaking, versioning a data object means recording its creation and deletion events, as well
as all changes to its attributes. For example, if a Great Quux’s email was [email protected] on
19 Jan. and changed to [email protected] on 12 Apr., the versioning service will have
a record of this.
In the event that this data object is rolled back to its 19 Jan. state, then the email address has to be
changed back to [email protected]. This is an example of versioning a scalar attribute.
We use the term scalar attribute to refer to a property that has a simple object type, such as BigInteger, Boolean, or String.
If the properties type of an object type are compound, they are referred to as compound attributes.
In Example 11-8, Country is a compound object type (the exact PDL definition is not shown for
the sake of brevity). Thus, the property country of the object type GreatQuux is a compound
attribute.
As the example of the email property demonstrates, the case of versioning scalar attributes is a
straightforward one, while compound attributes require a little extra care. Section 11.5.3 Recoverable
types explains another situation in which compound attributes require special treatment.
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11.5.3. Recoverable types
The case of compound attributes like country is a little more complex. Let’s look at Example 11-8
again. Suppose the Great Quux had Wonderland listed as his country of residence on Jan 19. On Apr
12, his country of residence changed to Eriador; the Wonderland data object was deleted altogether.
What should happen if we try to rollback the Great Quux to his Jan 19 state? Since the data object
is versioned, its country attribute should be rolled back to Wonderland. But Wonderland no longer
exits in the database. One solution is to set the country to null. This would not work in this case,
because this attribute is required - it has the multiplicity of 1..1. Therefore, we should be able to
recover the deleted data object.
This leads to the notion of a recoverable data object. A data object is recoverable if the versioning
service is able to undelete it after it has been deleted. Being recoverable is a weaker requirement than
being fully versioned. The versioning service may not be able to rollback a recoverable object back
to an arbitrary point in its history, but it should record enough information to undelete it, in case it is
ever deleted.
The versioning service infers that if a versioned object type has a required compound attribute,
then the object type of the attribute must be marked as recoverable. The versioning service does
not normally record changes to recoverable objects, but it keeps track of them in case they are deleted.
If a recoverable object is deleted, the versioning service records the last known values of its attributes
in order to be able to undelete it.
What does this mean in terms of Example 11-8? The versioning service treats the Country object
type as recoverable, because it is a required compound attribute of the versioned type GreatQuux.
Why not make the Country object type fully versioned? Because we don’t want to version more
data than is actually needed. If a developer wants to make the Country object type fully versioned,
they should explicitly mark it as such in the PDL definition.
What if the Country object type is marked as versioned? Should we rollback the country
attribute when we rollback the Great Quux object? We cannot. Since it is not a component of
GreatQuux, Country data objects may be included as an attribute by other object types. If we
rollback a country as part of rolling back the Great Quux object, we may affect a lot of other objects
that should not have been necessarily affected by this rollback.
11.5.4. Versioning service API
For backwards compatibility, some of the old versioning APIs are preserved. For example, you can
tag the state of a data object in the current transaction by calling the applyTag method on the VersionedACSObject class. However, this class has been deprecated.
The preferred point of entry into the API provided by the versioning service is the Versions class.
One important capability it has is providing methods for invoking the following functionalities:
1. Tagging the state of a data object in the current transaction. Note that you can tag the state of a
data object, even if no changes were made to it in the current transaction. You can also tag more
than one data object within the same transaction.
2. You can retrieve a collection of tagged transactions for a data object. Note that since the data
object may have been deleted, the method for retrieving the collection takes in an OID parameter
rather than a DataObject parameter.
3. You can roll a data object back to any previous point in its history.
4. You can compute the difference between any two states of a data object.
5. You can suspend versioning till the end of the current transaction.
Please refer to the Javadoc API at http://rhea.redhat.com/documentation/api/ccm-core-6.1.0 for details.
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11.5.5. PDL Syntax
To specify which object types should be versioned, developers can use the keywords versioned
and unversioned. Consider the following example.
versioned object type VT1 {
BigInteger[1..1] id = t_vt1.id INTEGER;
object key(id);
}
object type VT2 extends VT1 {
component UT3[0..n] ut3s = join t_vt2.id to t_ut3.vt2_id;
reference key(t_vt2.id);
}
object type C1 {
BigInteger[1..1] id = t_c1.id INTEGER;
A1[1..1] a1s = join t_c1.a1_id to t_a1.id;
component UT4[0..1] ut4 = join t_c1.ut4_id to t_ut4.id;
object key(id);
}
association {
VT2[0..1] vt2 = join t_c1.vt2_id to t_vt2.id;
component C1[0..n] c1s = join t_vt2.id to t_c1.vt2_id;
}
object type A1 {
BigInteger [1..1] id = t_a1.id INTEGER;
UT4[1..1] ut4 = join t_a1.ut4_id to t_ut4.id;
object key(id);
}
object type UT1 {
BigInteger[1..1] id = t_ut1.id INTEGER;
UT3[1..1] ut3attr = join t_ut1.ut3_id to t_ut3.id;
object key(id);
}
object type UT2 {
BigInteger[1..1] id = t_ut2.id INTEGER;
object key(id);
}
versioned object type VUT2 extends UT2 {
UT1[1..1] ut1 = join t_vut2.ut1id to t_ut1.id;
unversioned String[1..1] unverAttr = t_vut2.unver_attr VARCHAR;
unversioned component UT5[0..n] ut5 = join t_vut2.ut5id to t_ut5.id;
versioned UT6[0..n] ut6s = join t_vut2.ut6id to t_ut6.id;
reference key(t_vut2.id);
}
object type UT3 {
BigInteger[1..1] id = t_ut3.id INTEGER;
composite VT2[1..1] vt2 = join t_ut3.vt2_id to t_vt2.id;
object key(id);
}
object type UT4 {
BigInteger[1..1] id = t_ut4.id INTEGER;
object key(id);
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}
versioned object type VTC3 {
BigInteger[1..1] id = t_vtc3.id INTEGER;
object key(id);
}
object type C2 {
BigInteger[1..1] id = t_c2.id INTEGER;
composite VTC3[1..1] vtc3 = join t_c2.composite_id to t_vtc3.id;
object key(id);
}
object type UT5 {
BigInteger[1..1] id = t_ut5.id INTEGER;
object key(id);
}
object type UT6 {
BigInteger[1..1] id = t_ut6.id INTEGER;
object key(id);
}
Example 11-9. Sample PDL definitions
For the sake of brevity, Example 11-9 only has key attributes for object types and does not show
any scalar attributes.
The graph in Figure 11-8 provides a visual representation of the above PDL definitions. Wheat-colored
nodes represent object types that are marked as versioned in Example 11-9. There are two types
of edges. If an edge is labeled extends, it means that the type at the edge head extends, in the PDL
sense, the type at the edge tail. For example, VT2 extends VT1. This relationship is important, because
subtypes of a versioned type are also versioned.
The other kind of edge is one that shows attributes of an object type. For example, consider the edge
labeled rqd:ut3attr that connects UT1 and UT3. It means that the object type UT1 has a required
attribute ut3attr of type UT3.
There are two kinds of compound attributes that are important from the versioning point of view:
required (rqd) and components (cnt).
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Figure 11-8. PDL definition graph
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Based on Figure 11-8, the versioning service decides which object types should be versioned,
recoverable, or simply ignored. The result of this decision can be visualized as follows.
UT2
C2
rqd,cst:vtc3
VUT2
vnd:ut6srqd:ut1
UT6
UT1
VT1
VTC3
unv,cnt:ut5
UT5
rqd:ut3attr
VT2
cnt:ut3s
rqd,cst:vt2
cnt:c1s
UT3
C1
rqd:a1s
A1
cnt:ut4
rqd:ut4
UT4
Figure 11-9. Versioning dependence graph
Red-colored nodes indicate those object types that are fully versioned by virtue of being marked
versioned (vnd) or having a supertype that is marked vnd.
Pink-colored nodes represent those types that are co-versioned by virtue of being a component of a
versioned or co-versioned object type.
Yellow-colored nodes denote those types that are treated as recoverable by virtue of being a required
attribute of a versioned or recoverable type.
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Gray nodes represent types that are ignored by the versioning service.
There are two kinds of edges in Figure 11-9:
1. Unlabeled edges represent the subtype relationship between two nodes. For example, VUT2
extends UT2.
2. Labeled edges are those where the edge tail is an object type that has an attribute whose type
is the edge head. For example, VT2 has the component attribute c1s of type C1.
Four kinds of attributes are important from the versioning perspective: marked versioned (vnd),
marked unversioned (unv), required (rqd) and components (cnt).
11.5.6. Differences between WAF 5.2 and 6.0
If you used the versioning service in previous releases of WAF prior to and including 5.2, you will
notice a number of differences between the old and current implementation.
The old implementation operated on the domain object level. The current implementation operates on
the data object level. Key differences that stem from this are:
1. Previously, you had to subclass VersionedACSObject in order to make your domain objects
versioned. This is no longer necessary.
2. Consequently, you are no longer required to use the methods getMaster(), setMaster(),
etc. The notion of master is gone. Although marked deprecated, these methods remain in order
to provide some degree of backwards compatibility on the API level.
3. In the old versioning systems, calling the delete() method never actually deleted the underlying data object. It merely marked it as deleted via the is_deleted flag in the vc_objects table.
This was referred to as a soft delete. It was possible to hard-delete an object via the permanentlyDelete() method of the VersionedACSObject class. This is no longer supported. In
the current versioning system, all deletes are hard deletes.
As a consequence, it is no longer necessary to write queries such as this:
select
f.id, frob_name
from
frobs f,
vc_objects v
where
f.id = v.object_id
and v.is_deleted = ’0’;
Instead, one can simply write:
select
f.id, frob_name
from
frobs f
4. The old versioning provided the ability to turn off versioning on a per instance basis. The method
trackChanges() could be overloaded to tell the versioning service whether or not this domain
object wished to be versioned. The new versioning service no longer provides this capability.
What it offers instead is the ability to turn off versioning entirely until the end of the current
transaction by calling Versions.suspendVersioning().
It is possible to request that an attribute of an object be not versioned. For instance:
versioned object type Frob {
BigInteger[1..1] id = frobs.id INTEGER;
unversioned String[0..1] type
= frobs.type VARCHAR;
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String[1..1] name
= frobs.frob_name VARCHARA;
}
In the above example, the versioning system will ignore changes to the type attribute of the
Frob object type.
5. The current versioning service provides the ability to compute a diff between any two points in
history of a versioned data object. The old service did not provide a similar capability.
11.6. Search Tutorial
This section provides useful tutorials for the search service.
11.6.1. Making a domain object searchable
Making a domain object in an application searchable requires implementing and registering a metadata provider class. This adapter pattern enables the search service to extract the metadata it requires
from domain objects without requiring any specific knowledge of the application domain. The APIs
required to achieve this task are provided by a handful of classes from the com.arsdigita.search
package:
• MetadataProvider.java
• MetadataProviderRegistry.java
• ContentProvider.java
• ContentType.java
11.6.1.1. Core search metadata
The first task is to implement the MetadataProvider.java interface, providing the core search
metadata - the object’s locale, title and summary blurb. All the methods in this interface have a DomainObject as the first argument. The object supplied as the value for this argument will be an
instance (or subtype) of the object type specified when registering the provider with the MetadataProviderRegistry.
package com.example.binder;
import com.arsdigita.search.MetadataProvider;
import com.arsdigita.domain.DomainObject;
import com.arsdigita.util.StringUtils;
import java.util.Locale;
public class NoteMetadataProvider implements MetadataProvider {
public Locale getLocale(DomainObject dobj) {
Note note = (Note)dobj;
// Note doesn’t store the locale yet, so we just return null
return null;
}
public String getTitle(DomainObject dobj) {
Note note = (Note)dobj;
return note.getTitle();
}
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public String getSummary(DomainObject dobj) {
Note note = (Note)dobj;
// Truncate body text &amp; remove any HTML.
return StringUtils.truncateString(note.getBody(),
200,
true);
}
...
Example 11-10. Core search metadata
11.6.1.2. Supplementary search metadata
The next set of optional methods allow for provision of auditing data that will be useful for
narrowing search results, namely creation and modification date and the party who performed
these two actions. This information can be trivially provided if the domain object already using
com.arsdigita.auditing package:
...
public Date getCreationDate(DomainObject dobj) {
Note note = (Note)dobj;
BasicAuditTrail audit = BasicAuditTrail.retrieveForACSObject(note);
return audit == null ? null : audit.getCreationDate();
}
public Party getCreationParty(DomainObject dobj) {
Note note = (Note)dobj;
BasicAuditTrail audit = BasicAuditTrail.retrieveForACSObject(note);
return audit == null ? null : audit.getCreationParty();
}
public Date getLastMofidiedDate(DomainObject dobj) {
Note note = (Note)dobj;
BasicAuditTrail audit = BasicAuditTrail.retrieveForACSObject(note);
return audit == null ? null : audit.getLastModifiedDate();
}
public Party getLastMofidiedParty(DomainObject dobj) {
Note note = (Note)dobj;
BasicAuditTrail audit = BasicAuditTrail.retrieveForACSObject(note);
return audit == null ? null : audit.getLastModifiedParty();
}
...
Example 11-11. Supplementary search metadata
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11.6.1.3. Content provision
The remaining method to be implemented in the MetadataProvider interface is the one
that actually provides the searchable content. There are currently three formats in which
searchable content can be provided, each of which are identified by a static constant in the
com.arsdigita.search.ContentType class. Each search indexer will support a different set of
formats, so applications should implement as many formats as make sense.
•
TEXT - plain text, with no markup. Equivalent to text/plain mime type.
•
RAW - an arbitrary document format such as HTML, OpenOffice, PDF, RTF. The indexer will auto
detect which format and extract content for building the search index.
•
XML - a well formed XML document containing arbitrary elements. The indexer will extract content from the elements, keeping track of its XPath, enabling searches to be restricted by element
name.
The Lucene implementation in WAF supports the text content type, and InterMedia supports the RAW
and XML formats. The ContentProvider interface defines the API for providing content. The Note
object allows its body text attribute to store HTML, so there can be two implements of ContentProvider, one for TEXT, and the other for HTML. These are typically written as package private,
inner classes of the MetadataProvider implementation
...
class TextContentProvider implements ContentProvider {
privte Note m_note;
public TextContentProvider(Note note) {
m_note = note;
}
public String getTag() {
return &quot;Body Text&quot;;
}
public ContentType getType() {
return ContentType.TEXT;
}
public byte[] getBytes() {
String body = m_note.getBody();
// Strip out html tags
return StringUtils.htmlToText(body).getBytes();
}
}
....
Example 11-12. Text content provider
...
class HTMLContentProvider implements ContentProvider {
privte Note m_note;
public HTMLContentProvider(Note note) {
m_note = note;
}
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public String getTag() {
return &quot;Body Text&quot;;
}
public ContentType getType() {
return ContentType.RAW;
}
public byte[] getBytes() {
String body = m_note.getBody();
// Wrap the body HTML in a header and footer
return (&quot; html&gt; head&gt; title&gt;&quot; +
m_note.getTitle() +
&quot; /title&gt; /head&gt; body&gt;&quot; +
body +
&quot; /body&gt; /html&gt;&quot;).getBytes();
}
}
...
Example 11-13. Raw content provider
Finally to the getContent method in the MetadataProvider interface is used to wire in the supported ContentProvider implementations. This method returns an array of ContentProvider
objects for each type, for example, allowing an object which ’0..n’ file attachments to return each file
as raw content.
...
public ContentProvider[] getContent(DomainObject dobj,
ContentType type) {
Note note = (Note)dobj;
if (type == ContentType.TEXT) {
return new ContentProvider[] {
new TextContentProvider(note)
};
} else if (type == ContentType.RAW) {
return new ContentProvider[] {
new HTMLContentProvider(note)
};
} else {
return null;
}
}
Example 11-14. Wiring up the content providers
11.6.1.4. Metadata provider registration
The search service maintains a registry of which metadata provider adapters to use for each object
type. To activate searching of the Note domain object, its adapter must be registered. The registration process is typically done upon startup from the init(DomainInitEvent e) method of
com.arsdigita.runtime.Initializer. When determining which adapter to use for extracting
metadata, the search service will travel up the object type inheritance tree until it finds a registered
adapter. Thus if an application has a number of object types all inheriting from a common parent, it
may be sufficient to register the metadata provider against the parent type.
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package com.example.binder;
import com.arsdigita.runtime.CompoundInitializer;
import com.arsdigita.runtime.DomainInitEvent;
import com.arsdigita.search.MetadataProviderRegistry;
public class NoteInitializer extends CompoundInitializer {
public void init(DomainInitEvent evt) {
super.init(evt);
MetadataProviderRegistry.registerAdapter(
Note.BASE_DATA_OBJECT_TYPE,
new NoteMetadataProvider());
}
}
Example 11-15. Registering a provider
11.6.2. Creating a search user interface
This section of the tutorial outlines the steps required to add user interface for performing searches
of content within an application. The com.arsdigita.search.ui package contains a library of
components which serve as the building blocks for an application’s search UI. The main files of
interest are:
•
QueryComponent.java
•
BaseQueryComponent.java
•
ResultsPane.java
•
FilterComponent.java
11.6.2.1. Basic search form
The first step in building a search form is to create a form containing a text entry widget for the query
string. The QueryComponent class is a general purpose, abstract Bebop container implementing the
QueryGenerator interface. This interface provides a mechanism for retrieving a query specification
using the current page state without requiring any knowledge about the structure of the data entry
form (for that matter, there might not be any form at all!).
The BaseQueryComponent class is a simple subclass of QueryComponent providing a widget for
specifying the query string and APIs for adding filter components (more on these later). This is the
component to start with when creating a search UI for an application. The only pre-requisite is that is
be contained within a Bebop form.
QueryComponent query = new BaseQueryComponent();
Form form = new Form(&quot;search&quot;);
form.add(m_query):
form.add(new Submit(&quot;Search notes&quot;));
add(m_query);
Example 11-16. Creating a basic search form
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11.6.2.2. Displaying results
The next stage is to add functionality for processing the query specification and displaying the results. The ResultsPane takes care of both of these tasks, only requiring an implementation of the
QueryGenerator interface be passed into its constructor, which of course is already fulfilled by the
QueryComponent class.
ResultPane results = new ResultPane(query);
add(results);
Example 11-17. Adding a result pane
11.6.2.3. Filtering results
Since search is a system wide service, the result of the previous stage is a component that searches
every single object type for which there is a search metadata provider registered. For internal application search, a filter is required to restrict results to one or more object types. There is a choice of
two classes that can be used for this task, both part of the com.arsdigita.search.ui.filters
package.
• ObjectTypeFilterComponent a
into its constructor.
static component that restricts to the list of object types passed
• ObjectTypeFilterWidget a
dynamic widget that presents the list of object types passed into its
constructor in a form, enabling the user to restrict the search.
For the binder application, there is only a single object type, Note, so the ObjectTypeComponent is
most appropriate.
FilterComponent objTypeFilter =
new ObjectTypeFilterComponent(Note.BASE_DATA_OBJECT_TYPE));
query.add(objTypeFilter);
Example 11-18. Filtering by object type
11.6.2.4. Note search component
These three stages now all combine to form a NoteSearchComponent that can be dropped into pages
in the Binder application (or indeed any other application wishing to Note objects.
package com.example.binder.ui;
import com.example.binder.Note;
import
import
import
import
import
com.arsdigita.search.ui.BaseQueryComponent;
com.arsdigita.search.ui.QueryComponent;
com.arsdigita.search.ui.ResultPane;
com.arsdigita.search.ui.FilterComponent;
com.arsdigita.search.ui.ObjectTypeFilterComponent;
import com.arsdigita.bebop.Form;
import com.arsdigita.bebop.SimpleContainer;
import com.arsdigita.bebop.form.Submit;
public class NoteSearhComponent extends SimpleContainer {
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Chapter 11. Services Tutorials
private QueryComponent m_query;
private FilterComponent m_typeFilter;
private ResultsPane m_results;
public NoteSearchComponent() {
super(&quot;note:search&quot;, Note.XML_NS);
m_typeFilter = new ObjectTypeFilterComponent(Note.BASE_DATA_OBJECT_TYPE);
m_query = new BaseQueryComponent();
m_query.add(m_typeFilter);
m_results = new ResultsPane(m_query);
Form form = new Form(&quot;search&quot;);
form.add(m_query):
form.add(new Submit(&quot;Search notes&quot;));
add(m_query);
add(m_results);
}
}
Example 11-19. Completed search component
11.6.3. Providing a new Query engine
This section of the tutorial outlines the steps required to implement a new query engine for performing
searches against an external index.
MORE NEEDED HERE
11.6.4. Providing a new Search indexer
This section of the tutorial outlines the steps required to implement an search indexer which receives
update notifications when a domain object is changed, retrieves metadata and content and builds an
index.
From Dan ... to manually hack the PL/SQL for the ’sync_index’ method and remove the keyword
’online’ from the code. This will do offline rebuilds of the search index. The potential problem with
this is that this locks out any other threads touching the search index - including end user searches &amp;
metadata updates from authors editing content. As such it could severely impact on scalability, so EE
is definitely preferable to this.
MORE NEEDED HERE
Chapter 12.
Presentation (Bebop) Tutorial
This chapter provides useful tutorials for learning and exercising the presentation system using Bebop,
as introduced in Chapter 5 WAF Component: Presentation. The focus is primarily on integrating other
presentation methods such as CSS, CSL and JSP into WAF, while demonstrating how to use Bebop.
This chapter does not provide any general tutorials on these other tools. For a starting point to finding
tutorials about these methods, see Chapter 14 References.
12.1. Calling XSLT from a WAF Application
The gateway to XSLT from WAF is the PresentationManager interface, whose servePage
method selects a stylesheet to use, applies the selected stylesheet to an XML document, and sends
the output from the transformation to the client. This information was originally discussed in Section
5.2.1 Integrating XSLT with WAF.
The most commonly used implementation of PresentationManager is the provided BasePresentationManager, which searches for a stylesheet for a request by first looking for a stylesheet
associated with the active site node, then the parents of the active site node, and finally the default
stylesheet for the current package. It also takes the locale and output type for the request into account
when selecting stylesheets.
Any selected stylesheet may use the xsl:import or xsl:include tags to import rules from another
stylesheet. There are two common uses for this: a package’s default stylesheet will import stylesheets
from other packages that it depends on; and a customized stylesheet (for example, for a site node) can
import another stylesheet and the rules defined in the customized stylesheet will override conflicting
rules in the imported one.
Calling XSLT from WAF applications is transparent if you use Bebop — you pass a Bebop Page
object directly as an argument to BasePresentationManager.servePage(). That form of
servePage will save the step of explicitly generating an XML document as output from the Page
object:
Page p = ... Bebop page ...;
BasePresentationManager.getInstance().servePage(p, request,
response);
Any WAF application code that wants to render an XML Document object into HTML output directly, without using Bebop, would call the servePage method of PresentationManager using
approximately this pattern:
import com.arsdigita.templating.PresentationManager; import
com.arsdigita.xml.Document;
Document doc = ... generated document ...
// grab a presentation manager instance
PresentationManager pm = SomePMClass().getInstance();
pm.servePage(doc, request, response);
12.2. Handling Pre-Formatted Text
You may occasionally have HTML-preformatted text that you need to integrate into a Bebop component. This might come from a globalization translator, user input HTML, or as part of feed or
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Chapter 12. Presentation (Bebop) Tutorial
stream from an outside source. This section discusses methods for handling this pre-formatted text
intelligently.
WAF provides an explicit technique for this situation by using the Bebop Label component and by
disabling output escaping in the XSLT processor for the context of the label. The code:
Label l = new Label(&quot;This is a b new /b
l.generateXML(pageState, element);
label.&quot;, false);
will generate the XML fragment:
bebop:label escape=&quot;yes&quot; This is a &amp;lt;b new&amp;lt;/b&amp;gt;
label. /bebop:label
The result is that the HTML-preformatted text is a single, text-node child to the bebop:label element. On output, the escape=&quot;yes&quot; means that the angle brackets will not be output-escaped.
They will appear in the HTML stream as angle brackets and be interpreted as such by the user’s web
browser, causing the word new to appear in bold.
Note
The escape=&quot;yes&quot; attribute to bebop:label is confusing because it is shorthand for what will become the XSLT attribute disable-output-escaping=&quot;yes&quot;.
By default, the XSLT processor escapes output according to the output mode specified in the stylesheet
with the xsl:output element. This default makes angle brackets appear as angle brackets in the
user’s browser, which means they are transmitted as &amp;lt;’s in the HTML stream.
If you want angle brackets to show up in your output (e.g less-than signs for mathematics), you want
to enable output escaping, which is the default setting.
Label l = new Label(&quot;3.141
pi
3.142&quot;);
Caution
Inserting HTML formatting into the Bebop DOM, where it is difficult to style globally, is not generally
recommended.
An alternative solutions is to parse the string argument to the Label constructor as a DOM fragment,
instead of simply disabling output escaping, so that the formatting elements are a full-fledged part of
the DOM and eligible for global styling. A drawback to this is the expense of parsing XML.
An additional drawback is that most people do not write well-formed XHTML, while browsers are
much more tolerant than XML parsers. In other words, it is possible to write the following:
!
Label l = new Label(&quot; ul
/ul &quot;, false);
li
list item 1
li
list item 2
This will be displayed correctly as an unordered list in the browser, even though the label contents are
not well-formed [X]HTML.
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155
12.3. Site-Wide Master Pages
Usually the pages within the scope of a single application share a common layout. For example, all
of the pages may have the same four-panel layout: the same header, footer, and sidebar content, while
the main content of the page varies. Another way of looking at this is that the main content of each
page is enclosed in another master page.
There are two aspects to making shared-layout pages like this:
1. A declaration of page components in Java. With Bebop, the top-level Page object must contain the components that generate the dynamic content displayed in each of the header, footer,
sidebar, and main panels as DOM fragments.
2. An XSLT stylesheet to render the page properly. The XSLT stylesheet is responsible for selecting the content for each of the panels on the page, and placing them appropriately in the
output, with the right look-and-feel (color scheme, dimensions, etc.) Note that this means whatever DOM is generated by the page components above must allow for the XSLT stylesheet to
distinguish between the content that belongs in the header, footer, etc.
The preferred way to implement shared-layout pages like this in Bebop is to subclass Page. Users
of this class add components to the page as usual, but the page’s constructor and DOM-generation
methods are overloaded to pre-fill the page with the appropriate boilerplate components.
The following example is a Page that always contains a header, footer, and sidebar:
package com.arsdigita.bebop.demo;
import
import
import
import
com.arsdigita.bebop.*;
com.arsdigita.xml.*;
com.arsdigita.dispatcher.RequestContext;
com.arsdigita.dispatcher.DispatcherHelper;
/**
* This is a common page for a fictitious site, SockPuppet.com.
* It includes a common header, a footer, and a main &quot;content&quot;
* area. We override the .generateXML method to pre-fill the page
* with the boilerplate content.
*/
public class SockPuppetPage extends Page {
private Component m_top;
private Component m_bottom;
private Component m_side;
public SockPuppetPage() {
this(&quot;&quot;);
}
public SockPuppetPage(String s) {
super(&quot;SockPuppet.com: &quot; + s);
m_top = new SiteHeader();
m_bottom = new SiteFooter();
m_side = new SiteSide();
}
public void generateXML(PageState ps, Document doc) {
Element page = generateXML(doc);
Element layout = new Element(&quot;socksite:layout&quot;, SOCKSITE_XML_NS);
page.addContent(layout);
addContents(layout, ps);
}
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protected void addContents(Element layout, PageState ps) {
Element topPanel =
new Element(&quot;socksite:top&quot;, SOCKSITE_XML_NS);
layout.addContent(topPanel);
m_top.generateXML(ps, topPanel);
Element sidePanel =
new Element(&quot;socksite:side&quot;, SOCKSITE_XML_NS);
layout.addContent(sidePanel);
m_side.generateXML(ps, sidePanel);
Element bottomPanel =
new Element(&quot;socksite:bottom&quot;, SOCKSITE_XML_NS);
layout.addContent(bottomPanel);
m_bottom.generateXML(ps, bottomPanel);
Element mainPanel =
new Element(&quot;socksite:main&quot;, SOCKSITE_XML_NS);
layout.addContent(mainPanel);
m_panel.generateXML(ps, mainPanel);
}
/**
* Header component. Demonstrates dynamic content.
*/
private class SiteHeader extends Label {
public SiteHeader() {
super(new PrintListener() {
public void prepare(PrintEvent pevt) {
Label target = (Label)pevt.getTarget();
PageState ps = pevt.getPageState();
RequestContext rc =
DispatcherHelper.getRequestContext
(ps.getRequest());
target.setLabel(&quot;SockPuppet.com:
dynamic page header.&quot;
+ &quot; You requested: &quot; + rc.getOriginalURL());
}
}
}
}
/**
* Footer component. All static.
*/
private class SiteFooter extends Label {
public SiteFooter() {
super(&quot;SockPuppet.com: static footer.&quot;);
}
}
/**
* Sidebar component. All static.
*/
private class SiteSide extends Label {
public SiteSide() {
super(&quot;SockPuppet.com: static sidebar.&quot;);
}
}
}
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You would use this Page like any other, for example, Page p = new SockPuppetPage();
p.add(...); .... However, when you call buildDocument, the generated DOM will include all
of the content from the header, footer, etc.:
&quot;
bebop:page
#
&quot; &quot;
... some page boilerplate ...
##
socksite:top
bebop:label
SockPuppet.com: dynamic page header.
/bebop:label
/socksite:top
&quot; &quot;
&quot; &quot;
##
##
You requested: ...
socksite:side
bebop:label
SockPuppet.com: static side panel
/bebop:label
/socksite:side
&quot; &quot;
&quot; &quot;
##
# #
# #
socksite:bottom
bebop:label
SockPuppet.com: static footer
/bebop:label
/socksite:bottom
&quot; &quot;
&quot;
&quot;
#
socksite:main
... main contents here ...
/socksite:main
&quot;
/bebop:page
#
#
Note
The order of the components in the DOM may have nothing at all to do with the ordering of the output.
The page components just ensure that the right content is generated with the right logical structure.
It is up to the XSLT stylesheet to ensure that a socksite:top element really appears at the top of
the page.
You would need an XSLT template rule such as the following to convert the above DOM into meaningful XHTML output:
&quot;
!-- match the layout element and put the
header, footer, etc., in their appropriate places. --
&quot;
#
&quot;
xsl:template match=&quot;socksite:layout&quot;
xmlns:socksite=&quot;http://www.sockpuppet.com/xmlns&quot;
&quot; &quot; #
&quot;#
&quot; #&quot;
&quot; #
xsl:apply-templates select=&quot;socksite:top&quot;/
#&quot;
table
tr
td width=&quot;25%&quot;
xsl:apply-templates
select=&quot;socksite:side&quot;/
/td
td
xsl:apply-templates
select=&quot;socksite:main&quot;/
/td
/tr
#&quot; #
#&quot; #
#
#
158
$
$
$
Chapter 12. Presentation (Bebop) Tutorial
/table
%
xsl:apply-templates select=&quot;bebop:bottom&quot;/
/xsl:template
%
%
This template must be associated with the appropriate application (for example, the main SockSite
application) or site node.
12.4. Varying a Shared Layout
Once you have a shared-layout Page subclass, such as SockPuppetPage above, you will likely have
single pages that vary the boilerplate content slightly. For example, you might have a single page
which uses the same header, footer, and sidebar as all other pages on your site, but which adds an
extra boilerplate component above the header, such as a banner ad.
You can accomplish this with further sub-classing. You can define a subclass of SockPuppetPage,
BannerAdSockPuppetPage, which has all of the same pre-filled components but adds a second
header, a BannerAd component:
package com.arsdigita.bebop.demo;
import com.arsdigita.bebop.*;
import com.arsdigita.xml.*;
import com.arsdigita.dispatcher.RequestContext;
import com.arsdigita.dispatcher.DispatcherHelper;
// fictitious banner ad management system
import com.arsdigita.personalization.BannerAdManager;
public class BannerAdSockPuppetPage extends SockPuppetPage {
private Component m_banner_ad;
public BannerAdSockPuppetPage() {
this(&quot;&quot;);
}
public BannerAdSockPuppetPage(String s) {
// calling super() adds default header, footer, and sidebar
super(&quot;SockPuppet.com: &quot; + s);
m_banner_ad = new BannerAd();
}
public void generateXML(PageState ps, Document doc) {
Element page = generateXML(doc);
Element layout = new Element(&quot;socksite:layout&quot;, SOCKSITE_XML_NS);
page.addContent(layout);
// generate XML for header, footer, sidebar, and main panel
super.addContents(layout, ps);
// just add the new banner ad here
Element bannerAd = new Element(&quot;socksite:bannerAd&quot;,
SOCKSITE_XML_NS);
layout.addContent(bannerAd);
m_banner_ad.generateXML(ps, bannerAd);
}
/**
* Header component.
Demonstrates dynamic content.
Chapter 12. Presentation (Bebop) Tutorial
159
*/
private class BannerAd extends SimpleComponent {
public void generateXML(PageState ps, Element parent) {
Element elt = new Element(&quot;socksite:bannerAd&quot;,
SOCKSITE_XML_NS);
elt.setText(BannerAdManager.getInstance().getBanner());
parent.addContent(elt);
}
}
}
You must also amend the XSLT stylesheet:
&amp;
!-- match the layout element and put the
header, footer, etc., in their appropriate places. --
&amp;
'
&amp;
&amp;
xsl:template match=&quot;socksite:layout&quot;
xmlns:socksite=&quot;http://www.sockpuppet.com/xmlns&quot;
'
xsl:apply-templates select=&quot;socksite:top&quot;/
&amp; &amp; '
&amp;'
&amp;&amp; &amp; ' ' &amp;
'
&amp;
xsl:apply-templates select=&quot;socksite:bannerAd&quot;/
'&amp;
'
table
tr
td width=&quot;25%&quot;
xsl:apply-templates
/td
select=&quot;socksite:side&quot;/
td
xsl:apply-templates select=&quot;socksite:main&quot;/
/tr
/table
&amp;
'&amp; '
xsl:apply-templates select=&quot;bebop:bottom&quot;/
/xsl:template
(
'
Note
'
'&amp; '
/td
'
)
The above stylesheet will work whether or not the input DOM actually contains a banner ad; the
xsl:apply-templates select=&quot;socksite:bannerAd&quot;/ code will simply be ignored if no such
element exists in the DOM.
12.5. Special-Case Stylesheets
You may occasionally want to override the default stylesheet rules for one particular page. Because of
the way XSLT works, you can choose to override only some template match=... rules, allowing
others to be handled by the default stylesheet.
You should handle this in the dispatcher for your application, or by overriding the getStylesheetTransformer() or servePage methods in a PresentationManager class specific to your appli-
cation. For example:
public class SockPuppetPresentationManager extends
BasePresentationManager {
public void servePage(Page p,
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HttpServletRequest req,
HttpServletResponse resp)
throws IOException, ServletException {
RequestContext rctx = DispatcherHelper.getRequestContext(req);
String url = rctx.getRemainingURLPart();
// serve page as usual, except for URLs foo/*; those get a
// special-case stylesheet
if (!url.startsWith(&quot;foo/&quot;)) {
super.servePage(p, req, resp);
} else {
// use custom stylesheet for foo/*
// in reality, probably cache Transformer for performance
Stylesheet fooSS = ... get overridden rules
from somewhere ...;
Transformer xformer = fooSS.newTransformer();
Document doc = p.buildDocument(req, resp);
Writer out = resp.getWriter();
xformer.transform(new DOMSource(doc), new StreamResult(out));
}
}
}
12.6. UI Tutorial
The permissions UI provides reusable components for building customized permission administration
interfaces.
The default implementation of it resides under /permissions/. It supports a standard set of permissions: READ, WRITE, CREATE, DELETE, ADMIN. A user or group with admin privilege on an
object can share the privileges with other parties using this interface.
There are two requirements to show an object’s permission tables.
•
The viewing user must be authenticated by having logged so that the user ID can be read from the
user cookie.
•
The ACSObject ID must be in the page state as a global parameter (current implementation to
support URL redirects and URL referencing in WAF Tcl style).
The first step is to create the embedding Bebop Page for the permissions UI. A simple example is ObjectPermissionsPage.java. This only has a UserAuthenticationListener in the constructor and builds a PermissionsPane using the default constructor. Note, that the default constructor
will give you the permissions table with READ, WRITE, CREATE, DELETE, ADMIN privileges
(as defined in PermissionsConstants.java). You can use this to build permissions tables with a
privilege array customized for your application:
PermissionsPane(PrivilegeDescriptor[] privs)
The main class that provides components for the permissions UI is PermissionsPane. It has dual
functionality:
1. It implements the generic permissions UI for ACSObjects,
2. It provides getter methods to retrieve only parts of the interface.
If you use the PermissionsPane class directly, you get a UI layout equivalent to what you see
at http://yourhost.com/permissions/, using with your privileges instead. If you want to use
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161
only certain components of PermissionsPane, you must subclass it and overwrite the following
public methods:
public
public
public
public
void
void
void
void
register(Page p),
showAdmin(PageState s),
showGrant(PageState s),
showNoResults(PageState s).
The register determines which and how many components you are going to use. The showFoo methods manage visibility of components. You can also write your own visibility manager in the subclass
in a similar way, and just use that. You could also overwrite the other public methods, for example, to
provide alternative or static components for faster testing, or to save a member variable in the subclass.
Also, consider the reset() function.
The components that can be extracted from PermissionsPane are:
• public Party getRequestingUser(PageState s)
• public ACSObject getObject(PageState s)
• public Label getTitle()
• public String[] getPrivileges()
• private PermissionsTables getPermissionsTables()
• public SimpleContainer getDirectPermissionsPanel()
• public SimpleContainer getInheritedPermissionsPanel()
• public Form getUserSearchForm()
• public SimpleContainer getPermissionGrantPanel()
• public SimpleContainer getPermissionsHeader()
• public SimpleContainer getNoSearchResultPanel()
• public SimpleComponent getContextPanel()
These functions all use lazy instantiators, meaning they are not constructed until they are needed.
Therefore instantiating PermissionsPane alone is not expensive, the components are computed
only once and on the fly.
Note, if you want the same HTML style as in the default implementation, you MUST import the
permissions.xsl stylesheet in the application’s stylesheet, for example:
*
xsl:import href=&quot;../../content-section/xsl/permissions.xsl&quot;/
+
Otherwise the Bebop components are rendered in their default style.
12.7. Working With Formbuilder
The formbuilder service makes it possible for non-technical application administrators to build forms
(typically HTML forms). It has an API that lets developers mount those forms in an application. The
developer is responsible for the processing of the form whereas the administrator takes care of the
form elements and visual appearance.
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12.7.1. Implementing and Registering a Process Listener
Your process listener must be a named Java class in order for it to be used by a persistent form. If your
form listener needs certain parameters with specific names and data types, ensure that the listener
implements the com.arsdigita.formbuilder.AttributeMetaDataProvider interface.
You register the listener by going to the formbuilder admin interface mounted under /formbuilder.
On the index page, choose to add a new persistent form and supply the name of the listener that was
implemented.
You may now notify any application administrator that the form is ready for editing. If the listener implements the com.arsdigita.formbuilder.AttributeMetaDataProvider interface,
the formbuilder admin UI will make sure that the persistent form complies with this contract and
submits the parameters that the listener needs.
12.7.2. Mounting a Persistent Form in an Application
The
formbuilder
admin
UI
represents
persistent
forms
via
the
com.arsdigita.formbuilder.SimpleQuestionnaire class. You may retrieve an instance of
this class via its integer id or via the admin name that you specified in the admin UI (the admin name
is unique).
Once you have created the instance of SimpleQuestionnaire that you need, you have two options:
•
The dynamic option involves adding a com.arsdigita.bebop.MetaForm to the page and will
ensure that admin changes to the form will take immediate effect.
•
The static approach involves adding a normal Bebop com.arsdigita.bebop.Form to your application page so that admin changes to the form will take effect only after server startup.
The dynamic approach is more convenient for the administrator, in that he can immediately see how
the form will look in the application. However, if the page has a heavy load of users, the static approach is preferable, since it is much more efficient. This is because it does not dynamically build the
component hierarchy of the form on every request.
Your decision to use static or dynamic will be based upon your usage patterns. One good method to
follow is to use the dynamic approach when in heavy development of an application and it’s forms,
then switch to static when the pages go to the live server and are subject to public loads. It is usually
preferred to keep the approach static on a non-production, site-development server. When you switch
to the static approach, it is recommended to restart the server regularly (e.g. with a daily cron job) so
as to capture changes made by application administrators.
Example 12-1 is an example of static mounting of a persistent form. In this case, the form is built only
once upon server startup. The web server must be restarted for any changes to take effect.
Page applicationPage = new Page();
SimpleQuestionnaire questionnaire =
new SimpleQuestionnaire(new BigDecimal(&quot;773&quot;));
applicationPage.add(questionnaire.createComponent());
applicationPage.lock();
Example 12-1. Static Mounting of a Persistent Form
Example 12-2 is an example of dynamic mounting of a persistent form. Changes to the form by the
administrator will take immediate effect on the application page.
Chapter 12. Presentation (Bebop) Tutorial
Page applicationPage = new Page();
applicationPage.add(new MetaForm() {
public MetaForm() {
super(&quot;application_form_name&quot;);
}
public Form buildForm(PageState pageState) {
SimpleQuestionnaire questionnaire =
new SimpleQuesionnaire(new BigDecimal(&quot;773&quot;));
return questionnaire.createComponent();
}
}
);
applicationPage.lock();
Example 12-2. Dynamic Mounting of a Persistent Form
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Chapter 13.
Web Applications Tutorial
13.1. Support for Globalization
This section discusses the internationalization (I18n) features of Java and WAF, and how to use this
to localize web applications.
See Chapter 14 References for more references discussing the concepts of globalization.
WAF supports globalization in a variety of ways:
1. It allows the user to select a preferred Locale, either by registering a preference with WAF, or
by sending the appropriate Accept-Language HTTP header with each request.
2. It allows the user to send and receive data in the user’s preferred character set encoding.
3. It provides mechanisms for storing multiple localized versions of resources for an application.
This is true for both static and dynamic resources.
4. It offers APIs for creating and accessing these localized resources.
5. It provides a globalized WUI (Web User Interface) toolkit — for more information, see Section
5.4 Bebop - Reusable Web UI Components.
6. It allows stylesheets (used for styling of content) to be associated with more than one Locale,
thereby allowing you to create different layouts based on Locale. These will be applied automatically by the system as determined by the user’s preferred Locale.
13.2. Locale Negotiation
When a user requests a URL, the server determines the appropriate Locale for the request. It does
this by negotiating between the client’s preferences and the server’s capabilities.
All valid URLs on the server are associated with an instance of some application.
1. If that application instance has an associated Locale, this will be used as the Locale for the
request. If the application instance does not have an associated Locale, the server checks whether
the user has a preferred Locale as kept by the WAF preferences service.
2. If there is a preferred Locale, and if that Locale is supported by the application, that is the
chosen Locale for the request.
3. If there is not a preferred Locale the server continues on to check the Accept-Language HTTP
headers. Checking each of the values in this HTTP header in order of descending q-value, the
server selects the first one that is supported by the application being served.
4. If no Locale can be determined, the server finally selects the default Locale for the server as the
Locale for the request. This algorithm is well documented in the LocaleNegotiator class.
This negotiation allows applications to support one or many languages without interacting with other
applications on the system. Thus, your application automatically tries to present itself to the user in
his or her preferred language, regardless of the other applications running on that server.
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Note
If an application built on WAF relies on a service provided by another package, that package must
also be globalized and must support any languages the WAF application is intended to support.
For example, if your application relies on the places service to relate and/or present geographical
data, you must ensure that this service supports all the Locales that you wish your application to
support.
You can retrieve the Locale for the current request by calling the getLocale() method of the
current RequestContext. For example:
java.util.Locale locale =
DispatcherHelper.getRequestContext(request).getLocale();
System.out.println(&quot;The locale for the current request is: &quot;
+ locale.toString());
Another option, character set encoding negotiation (charset negotiation) is more complicated than
Locale negotiation.
13.3. ResourceBundles and MessageCatalogs
ResourceBundles 1 are Java classes for grouping localizable resources. The class also provides
methods for finding the appropriate ResourceBundle based on a Locale and for retrieving resources
from it by performing a lookup based on a key.
A ResourceBundle has a base name and optionally an associated Locale. A base name is a namespace used to group resources. A ResourceBundle without an associated Locale is the default ResourceBundle for that base name. If a ResourceBundle for a particular Locale hierarchy is not
found, the ResourceBundle with no associated Locale is used. These are used to store resources
that are common across all Locale instances.
The Locale hierarchy is simply the mechanism that is used to fall back from very specific Locales
to more generic ones. For example, from en_US_WIN95, the hierarchy falls back to en_US and then
to en and finally to the empty Locale.
Typically, one base name is used per application. That is, all resources for an application or service are
grouped in the same ResourceBundle. In cases where this is not convenient, different base names
can be used.
An example of the normal use of ResourceBundles is the notes application. The base name
it uses is com.arsdigita.notes.NotesResources. It groups all its localizable resources
into that ResourceBundle. On the other hand, the places service uses multiple base names,
since it maintains a large amount of data, which may not be needed by all developers. For
example, a developer might just want to translate the names of countries into a particular
language, and not require any other place data. Therefore, the places service divides its resources
into different base names, including com.arsdigita.places.CountriesResources,
com.arsdigita.places.USStatesResources and so on.
It is recommended that you use PropertyResourceBundle 2 to store static resources. Static resources remain the same for the lifetime of the running server. This includes strings on WUI elements
(such as form labels, page titles, and error messages) and names of objects that do not change frequently (such as country and city names).
1.
2.
http://java.sun.com/j2se/1.3/docs/api/java/util/ResourceBundle.html
http://java.sun.com/j2se/1.3/docs/api/java/util/PropertyResourceBundle.html
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167
For example, PropertyResourceBundles might appear as follows for a HelloWorld application,
in English, Spanish, and French:
HelloWorldResources_en.properties
hello_world=Hello world!
HelloWorldResources_es.properties
hello_world=Hola todo el mundo!
HelloWorldResources_fr.properties
hello_world=Salut tout le monde!
For dynamic resources, the MessageCatalog class is provided. Dynamic resources are those that
change while the server is running. Most of these have to do with user-contributed content, where
a user can be an administrator of the site or a regular user. For example, if the Categorization
service was internationalized and application users were to be allowed to create categories, the application could allow the user to create a category and name it in more than one language, or mark
the category name for translation into the different languages that the application supports. Since this
kind of data is hard to maintain in PropertyResourceBundles, it is stored it in database-backed
MessageCatalogs.
A MessageCatalog is simply a way to store ResourceBundles in the database. To use them,
you create a MixedResourceBundle . This inherits from Java’s ResourceBundle and combines
a PropertyResourceBundle and a MessageCatalog, which have the same base name, into one.
It does this by reading the PropertyResourceBundle from the file system and the MessageCatalog from the database.
No code goes into a MixedResourceBundle; all the code is in the superclass itself. A MixedResourceBundle for the notes application might appear as follows:
package com.arsdigita.notes;
import com.arsdigita.globalization.MixedResourceBundle;
public class NotesResources_en_US extends MixedResourceBundle {}
Note
This MixedResourceBundle is for the base name com.arsdigita.notes.NotesResources and the
Locale en_US. This stems from the ResourceBundle name and indicates the Locale associated
with the ResourceBundle. In this case, this ResourceBundle should contain resources in American
English.
13.4. Accessing Resources
The GlobalizedMessage class is specifically designed to facilitate management and access to localized resources. This class represents a single globalized resource. It contains the base name of the
ResourceBundle, which contains the resource and the key to use to lookup the resource, and an
optional array of arguments to interpolate into the localized resource using Java’s MessageFormat
168
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3
class. It also contains a localize(java.util.Locale) method, which is used to localize the
resource to a particular Locale.
You should use this class to represent all localizable data for your application. In Section 13.5 Globalization and Bebop, you will learn how to pass GlobalizedMessages to Bebop components so that
they will perform the lookup when it is time to display the localized resource to the user.
The following example demonstrates how to access the hello_world resource defined in PropertyResourceBundle. Assuming that those files are in the com.arsdigita.helloworld package,
you would create a GlobalizedMessage to represent that resource and localize it as follows:
GlobalizedMessage message = new GlobalizedMessage(
&quot;hello_world&quot;,
&quot;com.arsdigita.helloworld.HelloWorldResources&quot;
);
// print in English:
System.out.println((String) message.localize(new Locale(&quot;en&quot;, &quot;&quot;, &quot;&quot;)));
// print in Spanish:
System.out.println((String) message.localize(new Locale(&quot;es&quot;, &quot;&quot;, &quot;&quot;)));
// print in French:
System.out.println((String) message.localize(new Locale(&quot;fr&quot;, &quot;&quot;, &quot;&quot;)));
The output will appear as:
Hello world!
Hola todo el mundo!
Salut tout le monde!
You can also make a parameter out of resources that will be interpolated using the MessageFormat
class. The next example will use the following PropertyResourceBundles:
WineResources_en.properties
this_wine_is=This is a {0} wine.
wine_color=red
WineResources_es.properties
this_wine_is=Este es un vino {0}.
wine_color=rojo
WineResources_fr.properties
this_wine_is=C’est un vin {0}.
wine_color=rouge
It is possible to create a GlobalizedMessage to perform the proper interpolation of the resource.
For example, this works if the wine_color resource is retrieved from a MessageCatalog and is not
stored statically in the PropertyResourceBundle.
GlobalizedMessage message = new GlobalizedMessage(
&quot;this_wine_is&quot;,
&quot;com.arsdigita.wine.WineResources&quot;,
{&quot;wine_color&quot;}
);
3.
http://java.sun.com/j2se/1.3/docs/api/java/text/MessageFormat.html
Chapter 13. Web Applications Tutorial
169
// print in English:
System.out.println((String) message.localize(new Locale(&quot;en&quot;, &quot;&quot;, &quot;&quot;)));
// print in Spanish:
System.out.println((String) message.localize(new Locale(&quot;es&quot;, &quot;&quot;, &quot;&quot;)));
// print in French:
System.out.println((String) message.localize(new Locale(&quot;fr&quot;, &quot;&quot;, &quot;&quot;)));
The output will appear as follows:
This is a red wine.
Este es un vino rojo.
C’est un vin rouge.
Note
When a key is not found in a ResourceBundle, or when the ResourceBundle is not found at all,
the localize(java.util.Locale) method returns the key. This is done for two reasons: first, it is
more user-friendly to display the key than it is to display an exception or error message. Second,
this method makes it easier for a translator to see all the resources that need to be translated on a
particular page.
Caution
There are GlobalizedMessage constructors that do not have the base name of the ResourceBundle
as a parameter. When these constructors are used, the base name of the ResourceBundle for the
current application is used. This information is retrieved from the current ApplicationContext.
Using these constructors is discouraged because the method is non-deterministic with regard to
changes in the application stack. For example, if an application written by one developer — e.g.
notes — runs on top of a portal application written by another developer, and it is using these
certain GlobalizedMessage constructors, an error can occur.
The first application is no longer the current running application, and therefore the base name of the
ResourceBundle for the GlobalizedMessages will be set incorrectly. It will be set to the base name
of the ResourceBundle for the Portal application.
Only use these constructors if you are sure that your application will always be at the top of the
application stack.
13.5. Globalization and Bebop
Bebop is enabled to use GlobalizedMessages wherever the localizable content is displayed to the
user.
To display localized content to the user using Bebop, pass a GlobalizedMessage to the Bebop
widget. For example, to write a globalized HelloWorld page using Bebop:
package com.arsdigita.helloworld;
import com.arsdigita.bebop.Label;
import com.arsdigita.bebop.Page;
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import com.arsdigita.dispatcher.Dispatcher;
import com.arsdigita.globalization.GlobalizedMessage;
public class HelloWorldDispatcher extends Dispatcher {
// do some stuff, set up URL to method map, etc.
private Page buildHelloWorldPage() {
Label message = new Label(new GlobalizedMessage(
&quot;hello_world&quot;,
&quot;com.arsdigita.helloworld.HelloWorldResources&quot;
));
Page page = new Page(message);
page.add(message);
page.lock();
return page;
}
}
When the Page is served, Bebop will automatically call the localize(java.util.Locale)
method of each of the GlobalizedMessages on the Page with the Locale of the current request as
an argument. This will allow the pages to be displayed to each user in his or her preferred language.
13.6. Localizing Stylesheets
WAF uses XSL stylesheets to lay out XML content that is usually produced by Bebop, but which
could be produced by other sources. For more information, see Section 5.4 Bebop - Reusable Web UI
Components. These stylesheets can be associated with Locales. This allows a developer to lay out a
Page differently based on Locale.
Stylesheets can also contain static text. This text can be translated in another stylesheet that is associated with the appropriate Locale.
The system selects the stylesheet to use for each request by matching it to the Locale of the current
request. It performs matching in the same way that ResourceBundles do, by using the Locale
hierarchy.
13.7. Sending Mail Messages
Sending Plain Text Messages
Plain text messages can be sent using a static convenience method:
Mail.send(to, from, subject, body);
You can use the standard format for email addresses, for example, [email protected],
Person [email protected], and Person LastName [email protected]. Mul-
tiple recipients can be specified in a single string separated by commas.
To access the complete set of header attributes, create a Mail object, invoke the various set
methods, and call send:
Mail msg = new Mail();
msg.setTo(&quot;User1 [email protected], User2 [email protected]&quot;);
msg.setFrom(&quot;Me [email protected]&quot;);
msg.setReplyTo(&quot;User3 [email protected]&quot;);
msg.setCc(&quot;User4 [email protected]&quot;);
msg.setBcc(&quot;User5 [email protected]&quot;);
msg.setSubject(&quot;this is the subject&quot;);
msg.setBody(&quot;this is the body&quot;);
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171
msg.send();
Sending Rich Text Messages
Rich text messages (i.e. HTML) require using the setBody(html,alternate) method to
specify both the HTML and plain text versions of a message to send out:
, -
, -
Mail msg = new Mail(to, from, subject);
msg.setBody(&quot; p This is the HTML body /p &quot;,
&quot;This is the plain text body&quot;);
msg.send();
Attachments
Message attachments are handled using one of the various attach(...) methods. Support is
provided for File, URL and ByteArray datasources. The URL datasource is the simplest to use
(and can also fetch from a local file using the appropriate protocol specification). All attachments require a name, a description, and an optional disposition. The MIME type is determined
automatically.
For example, the following code fragment shows how to attach an image whose content is fetched
from a URL:
URL url = new URL(&quot;http://example.com/image.gif&quot;);
Mail msg = new Mail(to, from, subject, body);
msg.attach(url, &quot;image.gif&quot;, &quot;A sample image&quot;);
msg.send();
The protocol for attaching content from a local file is similar:
File path = new File(&quot;image.gif&quot;);
Mail msg = new Mail(to, from, subject, body);
msg.attach(path, &quot;image.gif&quot;, &quot;A sample image&quot;);
msg.send();
The Mail service provides a utility class called ByteArrayDataSource that can be used to
attach virtually any type of content contained in memory by supplying its data as a byte[]
array.
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Chapter 14.
References
The following references are pointers to additional information that is relevant to WAF but beyond the
scope of this guide.
Martin Fowler’s book Patterns of Enterprise Application Architecture covers many of the design patterns used in WAF. For more information, see http://www.martinfowler.com/books.html#eaa.
For more information regarding object-relational persistence see the following third-party links:
•
http://www.rational.com/products/whitepapers/296.jsp
•
http://www.ambysoft.com/persistenceLayer.pdf
The OpenACS (http://www.openacs.org) project is the community-driven development of the previous generation Web Application Framework architecture written in the TCL programming language.
Many of the design concepts that appear in Red Hat WAF had precursors in the ACS TCL and OpenACS world. In particular:
•
http://openacs.org/doc/openacs-4-6-3/object-system-design.html is the design document that covers the basic object model that was the ancestor of the WAF object model.
•
http://openacs.org/doc/openacs-4-6-3/groups-design.html discusses the basic groups model that
was the ancestor of the current WAF group model.
The Java programming language provides extensive support for globalization:
•
The java.text Java
summary.html).
This
classes.
package
class
(http://java.sun.com/j2se/1.3/docs/api/java/text/packagecontains
most
of
Sun’s
globalization
•
The java.util.Locale class is Sun’s representation of a Locale, and can be found at
http://java.sun.com/j2se/1.3/docs/api/java/util/Locale.html.
•
The
java.util.ResourceBundle
class
and
its
maintain and retrieve externalized localized resources. It
http://java.sun.com/j2se/1.3/docs/api/java/util/ResourceBundle.html.
subclasses
help
can be found at
The official W3C Recommendations are the definitive references on XSLT, XPath expressions, and
related standards.
•
XSLT — (http://www.w3.org/TR/xslt)
•
XPath — (http://www.w3.org/TR/xpath).
•
XHTML 1.0 (http://www.w3.org/TR/xhtml1).
•
Canonical XML 1.0 (http://www.w3.org/TR/xml-c14n).
Section C.2 Java Coding Standards — References and Related Reading has links to Java coding
standards and best practices.
174
Chapter 14. References
III. Appendixes
Table of Contents
A. Bebop Tag Library Reference................................................................................................... 177
B. PL/SQL Standards ..................................................................................................................... 181
C. Java Standards ........................................................................................................................... 187
D. PDL Syntax................................................................................................................................. 189
Persistence Glossary ....................................................................................................................... 203
Appendix A.
Bebop Tag Library Reference
A.1. Bebop/JSP
.
Tag
show:all/
Description
/
Simplifies showing all the components of a
page. One such directive is the equivalent of
including a show:component directive for
each component you have defined for your page
.
.
.
/
show:page [pageClass=...]
[pmClass=...] [master=...]
/show:page
/
show:component name=... /
..
show:form name=...
/show:form
..
show:list name=... ...
show:listItem/ ... /show:list
/
/
Sets up a Bebop page for use in the JSP. Page is
specified by class name (pageClass). The
pageClass option is omitted if the page is set
up in the same JSP (by including a
page-definition JSP) or within a master page.
The resulting XML produced by the JSP is then
displayed by the presentation manager class
specified by pmClass (default
BasePresentationManager).
...
.
/
Shows a component from the Bebop page in the
JSP. There is no need for more specific tags for
each component here. The component is
displayed with default global styling.
Shows a form from the Bebop page in the JSP. If
the form tag contains a body, it is not displayed
with the default global styling though the
form tag and page state (input
type=hidden...) will be preserved. If the tag
body is empty, though, the entire form will be
displayed with default styling.
...
/ / .
/
/
0
1
Shows the contents of a model-backed List from
Bebop page in the JSP. The body of the tag will
be displayed for each item of the list, so this tag
is effectively a loop. The list itself is not
displayed with the default global styling though
the individual list items contained within will be
where indicated by show:listItem/ . Like
with show:form, if the tag body is empty, the
entire list will be displayed with default styling.
0
.
show:slave/
/
1
Includes the contents of the slave page into this
point in the master page.
Table A-1. Tags available for displaying Bebop components
178
Appendix A. Bebop Tag Library Reference
A.2. Available Page Definition Tags
Caution
These tags are highly experimental.
2
Tag
Description
define:page name=&quot;...&quot; title=&quot;...&quot;
[pageClass=&quot;...&quot;]
The define:page tag is the top-level tag for
Bebop-JSP integration, and it is responsible for
several processing actions:
— Declaring a Bebop Page object.
— Generating an XML document from Bebop.
— Putting this XML document into the request
attributes for the show:page tags.
name is the name of the pageContext attribute
that refers to the Bebop page. The optional
pageClass attribute is the name of the Page
class that will be used as the base class for the
created page.
2
define:image [name=...] src=...
[height=...] [width=...] [alt=...]
[border=...]/
Creates an Image object at this point in the
page.
2
Creates an Link object at this point in the page.
3
2
define:link [name=...] url=.../
3
3
define:form name=... [method=...]
[action=...] [encType=...]
2
3
The define:form tag indicates that a Bebop
form should be created at this particular location
in the page.
define:text name=... [size=...]
[maxLength=...] [type=...]/
Creates a TextField at this particular location
in the page.
define:textArea name=...
[rows=...] [cols=...]
[wrap=&quot;nowrap|soft|hard&quot;]/
Creates a TextArea at this particular location in
the page.
2
2
3
3
define:submit name=... [label=...]
[bundle=...]/
2
2
define:radioGroup name=...
3
3
Creates a radio group. Must be enclosed within
a form.
Creates a checkbox group. Must be enclosed
within a form. Checkboxes are arranged
horizontally by default, but can be arranged
vertically with the vertical attribute.
define:checkboxGroup name=...
[vertical=&quot;true&quot;]
2
2
define:select name=...
3
define:multipleSelect name=...
Creates a form submit button at this particular
location in the page, with an optional specified
label. If a resource bundle is specified the label
is used as a key.
3
Creates a selection widget. Must be enclosed
within a form.
Creates a multi-selection widget. Must be
enclosed within a form.
Appendix A. Bebop Tag Library Reference
4
Tag
Description
5
define:option name=... [value=...]
[selected=...] [bundle=...] /
4
179
define:component classname=...
5
defines an option within a select widget or
checkbox/radio group.
Creates a component of the given class and adds
it at the current location in the page. Requires
that the component class have a no-argument
constructor.
Table A-2. Tags available for defining Bebop components
Note that if a JSP tag does not exist for adding a particular component to a page, it is trivial to create.
As a last resort, you can use the generic define:component tag if the class has a no-argument
constructor. It is also trivial to escape into Java from a JSP and create a component object explicitly
in a Java scriptlet:
4 4
define:page name=&quot;p&quot; title=&quot;page title&quot;
%
MyComponent c = new MyComponent();
p.add(c);
%
/define:page
4 5
5
5
180
Appendix A. Bebop Tag Library Reference
Appendix B.
PL/SQL Standards
Like any other part of WAF, PL/SQL code must be maintainable and professional. This means that
it must be consistent and therefore must abide by certain standards. The standards will ensure that
our product will be useful long after the current people building and maintaining it are around. This
chapter addresses some standards and guidelines that will help us achieve this goal.
This chapter is written from the experience and perspective of the Red Hat Applications development
team. Because our product is open source, these standards are useful for all developers to understand
and incorporate.
B.1. General
1. All PL/SQL code must be well documented. We must write code that is maintainable by others.
This is especially true in our case because we are building an open source toolkit, so anyone can
download and browse the source code. Our motto is, &quot;Document like you are trying to impress
your favorite programming professor.&quot;
2. It is important to be consistent throughout an application as much as is possible given the nature
of team development. This means carrying style and other conventions such as naming within
an application, not just within one file.
B.2. Coding Standards
1. Encapsulation of related functionality is key to making our software maintainable and upgradeable. Try to bundle your code into packages whenever possible. This will make upgrading, bug
fixing, customizing, and many other things, a possibility.
2. When creating functions or procedures, use the following template. It demonstrates most of the
guidelines set forth in this document that correspond to functions and procedures:
66
77
77 6
66
create or replace procedure|function proc_or_func_name
param_1
in|out|inout datatype ,
param_2
in|out|inout datatype ,
...
param_n
in|out|inout datatype
)
[return datatype ]
is
local_var_1
datatype
local_var_2
datatype
...
local_var_n
datatype
begin
...
end proc_or_func_name ;
/
show errors
6
6
66
6
6
7
7
77
7
6
6
66
7
(
7
7
77
7
6
7
3. Always use create or replace procedure|function proc_or_func_name . It
makes reloading packages much easier and painless to someone who is upgrading or fixing a
bug.
182
Appendix B. PL/SQL Standards
8
9
4. Always qualify end statements. The end statement for a package should be end
package_name ;, not just end;. The same is true for procedures, functions, package
bodies, and triggers.
5. Always use the show errors SQL*Plus command after each PL/SQL block. It will help you
debug when there are compilation errors in your PL/SQL code.
6. Name parameters as simply as possible. That is, use the column name if the parameter corresponds to a table column. The syntax v_* and *_in is being deprecated in favor of the named
parameter notation. Therefore, of these two examples, the first one is preferred:
9
9
acs_user.create(first_names = ’Jane’,
last_name = ’Doe’, etc.)
acs_user.create(first_names_in = ’Jane’,
last_name_in = ’Doe’, etc.)
9
9
To achieve this we must fully qualify arguments passed into procedures or functions when using
them inside a SQL statement. This will get rid of any ambiguities in your code by telling the
parser when you want the value of the column and when you want the value from the local
variable.
For example:
create or replace package body mypackage
.
.
procedure myproc(party_id in parties.party_id%TYPE) is begin
.
.
delete
from parties
where party_id = myproc.party_id;
.
.
end myproc;
.
.
end mypackage;
/
show errors
7. Explicitly designate each parameter as in, out, or inout.
8. Each parameter should be on its own line, with a tab after the parameter name, then
in/out/inout, then a space, and finally the datatype.
9. Use %TYPE and %ROWTYPE whenever possible.
10. Use t and f for booleans, not the PL/SQL boolean datatype because it cannot be used in SQL
queries.
11. All new functions (for example, acs_object.new, party.new, etc.) should optionally accept an ID:
create or replace package acs_object
as
function new (
object_id
in acs_objects.object_id%TYPE default null,
object_type
in acs_objects.object_type%TYPE default ’acs_object’,
creation_date
in acs_objects.creation_date%TYPE default sysdate,
creation_user
in acs_objects.creation_user%TYPE default null,
creation_ip
in acs_objects.creation_ip%TYPE default null,
context_id
in acs_objects.context_id%TYPE default null
) return acs_objects.object_id%TYPE;
Appendix B. PL/SQL Standards
183
The function above takes the optional argument object_id. Do this to allow people to use the
same API call when they are doing double-click protection. That is, they have already gotten an
object_id and now they want to create the object with that object_id.
B.3. Coding Style
Some general style guidelines to follow for the purpose of consistency across applications.
1. Standard indentation is four spaces. Our PL/SQL code is not only viewable in the SQL files
but also through our SQL and PL/SQL browsers. This means that we should try to make it as
consistent as possible to all source code readers.
2. Lowercase everything, with the exception of %TYPE and %ROWTYPE.
B.4. Constraint Naming Standards
A constraint naming standard is important for one primary reason: The SYS_* name Oracle assigns to
unnamed constraints is not very understandable. By correctly naming all constraints, we can quickly
associate a particular constraint with our data model. This gives us two real advantages:
•
We can quickly identify and fix any errors
•
We can reliably modify or drop constraints
Why do we need a naming convention? Oracle limits names, in general, to 30 characters, which is
hardly enough for a human-readable constraint name.
B.4.1. Abbreviations
We propose the following naming convention for all constraints, with the following abbreviations
taken from the Oracle documentation. Note that we shortened all of the constraint abbreviations to
two characters to save room.
:
Constraint type
Abbreviation
references (foreign key)
fk
unique
un
primary key
pk
check
ck
not null
nn
; :
; :
B.4.2. Format of Constraint Name
table name _ column_name _ constraint abbreviation
;
In reality, this won’t be possible because of the character limitation on names inside Oracle. When
the name is too long, we will follow these steps in order:
&lt;
1. Abbreviate the table name with the table’s initials (for example, users - uc).
&lt;
u and users_contact
184
Appendix B. PL/SQL Standards
2. Truncate the column name until it fits.
create table example_topics (
topic_id
integer
constraint example_topics_topic_id_pk primary key
);
create table constraint_naming_example (
example_id
integer constraint cne_example_id_pk primary key,
one_line_description varchar(100)
constraint cne_one_line_desc_nn not null,
body
clob,
up_to_date_p
char(1) default(’t’)
constraint cne_up_to_date_p_check check(up_to_date_p in (’t’,’f’)),
topic_id
constraint cne_topic_id_nn not null
constraint cne_topic_id_fk references example_topics,
-- Define table level constraint
constraint cne_example_id_one_line_unq
unique(example_id, one_line_description)
);
Example B-1. Example of Constraint Name
Note
• If you have to abbreviate the table name for one of the constraints, abbreviate it for all the con-
straints.
•
If you are defining a multicolumn constraint, try to truncate the two column names evenly.
B.4.3. Naming primary keys
Naming primary keys might not have any obvious advantages. However, in Example B-2, the primary key helps make the SQL query clearer.
SQL
=
=
set autotrace traceonly explain;
SQL select * from constraint_naming_example, example_topics
where constraint_naming_example.topic_id = example_topics.topic_id;
Execution Plan
---------------------------------------------------------0
SELECT STATEMENT Optimizer=CHOOSE
1
0
NESTED LOOPS
2
1
TABLE ACCESS (FULL) OF ’CONSTRAINT_NAMING_EXAMPLE’
3
1
INDEX (UNIQUE SCAN) OF ’EXAMPLE_TOPICS_TOPIC_ID_PK’ (UNIQUE)
Example B-2. Primary Key Naming
Being able to see EXAMPLE_TOPICS_TOPIC_ID_PK in the trace helps us to know exactly which table
Oracle is querying.
If we had not named the constraints, the execution plan would look like:
Appendix B. PL/SQL Standards
185
Execution Plan
---------------------------------------------------------0
SELECT STATEMENT Optimizer=CHOOSE
1
0
NESTED LOOPS
2
1
TABLE ACCESS (FULL) OF ’CONSTRAINT_NAMING_EXAMPLE’
3
1
INDEX (UNIQUE SCAN) OF ’SYS_C00140971’ (UNIQUE)
The SYS_C00140971 by itself provides no information as to which index is being used in this query,
and more importantly, the name of this constraint will vary from database to database.
Mark Lindsey (&lt;[email protected]&gt;) provided another good reason to name primary keys and
unique constraints. Oracle creates an index for every primary key and unique constraint with the
same name as the constraint. It is an unfortunate DBA who has to wrestle with storage management
of tens of mysteriously-named indexes.
B.4.4. Naming not null Constraints is Optional.
Red Hat Applications developers are undecided on whether or not to name not null constraints. If
you want to name them, please do so and follow the above naming standard. Currently, naming not
null constraints is not a requirement of WAF.
Note
Naming the not null constraints does not help immediately in error debugging (for example the
error will say something like Cannot insert null value into column). We do recommend naming not
null constraints to be consistent in our naming of all constraints.
B.4.5. Upgrade Scripts
Data model upgrade scripts are a crucial part of database-based applications. Standards help to ensure
that upgrade scripts behave correctly and consistently. This helps save time in development, maintenance, and support.
Tip
An upgrade script should be written anytime that a change is made to a component’s sql creation
script that results in a different schema and/or data set. The new upgrade script should be written so
that, when applied to the previous creation script, it results in the same schema and data set.
Every component should have exactly zero or one upgrade script per release per supported database.
However, an upgrade script may source other files.
&gt;
? &gt;
? &gt;
Upgrade scripts go in an upgrade/ directory below the directory containing the corresponding creation script. The name of the file should be component-name - old-version-name - newversion-name .sql.
Example:
?
cms/sql/oracle-se/upgrade/cms-4.6.4-4.6.5.sql
186
Appendix B. PL/SQL Standards
@
Extending this process farther, there should be a single upgrade script for all of WAF per version. This
upgrade script lives in kernel/sql/oracle-se/upgrade and is called core-platform- oldversion-name - new-version-name .sql.
A @
A
Similar to core-platform-create.sql, this script will not have its own SQL commands, but will
simply source other files. Updating this script is the responsibility of each component developer.
Appendix C.
Java Standards
A good developer knows that there is more to
development than programming. A great developer knows that there is more to development than development.
(Ambler, 1999)
The purpose of this document is to establish a set of standards for any code written in Java for use in
WAF.
Why have conventions?
•
Most of the lifetime cost of a piece of code is maintenance.
•
Over its lifetime, code is usually maintained by people other than the original author.
•
Conventions improve the readability of code by providing a consistent level of quality.
•
Open source code is shipped as one of the pieces of the product. The code must be as clean and
well packaged as other pieces of the product.
•
Code is not written for compilers alone. People read your code, and style matters. For an approach
to English, a good starting point is The Elements of Style by Strunk &amp; White 1.
C.1. WAF Standards
In general, when programming for WAF, follow the Sun Java, JSP, and Javadoc conventions:
•
Code
Conventions
for
the
Java
Programming
http://java.sun.com/docs/codeconv/html/CodeConvTOC.doc.html
Language
—
•
Code Conventions for the JavaServer Pages Technology Version 1.x Language —
http://developer.java.sun.com/developer/technicalArticles/javaserverpages/code_convention/
•
Writing Javadoc comments — http://java.sun.com/j2se/javadoc/writingdoccomments/index.html
This chapter discusses WAF coding conventions where they differ from the Sun conventions or if they
cover something that is not in the standard convention.
1. Import statements should be alphabetized, separated into sections of relevant functionality, and
enumerated without using *.
2. All lines of source code should be indented uniformly using spaces and not tabs. Four spaces
is the norm, although in some cases more space is required. Two spaces is forbidden under all
circumstances.
3. Class fields, unless constants, are private. A private field called foo is named m_foo. A static
private field called foo is named s_foo.
4. Exceptions are used to signal erroneous behavior or usage inside of a class. All stubbed methods
should throw a runtime Error or UnsupportedOperationException with appropriate comments.
Do not write generic catch (Exception e) blocks; catch the specific exceptions instead.
1.
http://www.bartleby.com/141/.
188
Appendix C. Java Standards
5. Acronyms, such as JDBC or URL, should always be capitalized when used. For instance, write
JDBCLoader instead of JdbcLoader. This makes it clear that the letters are part of an acronym
and is easier to read because it matches how it is referred to in English prose. Abbreviations that
are not acronyms should have their first letter capitalized, with the exception of ID.
6. When debugging, avoid using System.out.println or System.err.println. Instead, use
Log4j as described in Section 7.5 Using logging for debugging.
C.2. Java Coding Standards — References and Related Reading
•
Ambler,
S.W.
(1999)
Writing
http://www.ambysoft.com/javaCodingStandards.html.
Robust
Java
•
Davis,
M.
(2000)
Incremental
Development
with
http://www-4.ibm.com/software/developer/library/j-ant/index.html.
•
Hunt,
A.
&amp;
Thomas,
D.
(1999)
The
http://www.pragmaticprogrammer.com/ppbook/index.shtml.
•
Sun (1999) Code Conventions for the Java™ Programming
http://java.sun.com/docs/codeconv/html/CodeConvTOC.doc.html.
•
JUnit Home Page — http://www.junit.org/
•
Ant home page — http://jakarta.apache.org/ant/.
Ant
Pragmatic
Code
and
—
JUnit
—
Programmer
—
Language
—
Appendix D.
PDL Syntax
This chapter introduces the syntax for the Persistence Definition Language.
D.1. PDL Grammar
The following is an Extended Backus-Naur Form (EBNF) grammar that defines the current PDL
language. EBNF is a standard notation for formally defining a language that extends BNF (they are
functionally equivalent -- EBNF simply introduces some elements for better readability).
B
C
ITEM
are terminals (tokens), while
In this grammar, items within angle braces
those not within angle brackets are non-terminals. If you are unfamiliar with EBNF,
http://www.garshol.priv.no/download/text/bnf.html is a good starting point.
/** Top level constructs. */
file :=
model &lt;SEMI&gt;
( pdl_import &lt;SEMI&gt; )*
( object_type | association | data_operation )*
&lt;EOF&gt;
model := &lt;MODEL&gt; idpath
pdl_import := &lt;IMPORT&gt; idpath ( &lt;DOT&gt; &lt;STAR&gt; )?
object_type :=
( &lt;VERSIONED&gt; )?
( &lt;QUERY&gt; | &lt;OBJECTTYPE&gt; ) id
( ( &lt;EXTENDS&gt; type |
&lt;CLASS&gt; javaClass &lt;ADAPTER&gt; javaClass |
&lt;RETURNS&gt; &lt;INT&gt; &lt;DOT&gt; &lt;DOT&gt; ( id | &lt;INT&gt; ) ) )?
&lt;LBRACE&gt; ( statement )* &lt;RBRACE&gt;
association :=
&lt;ASSOCIATION&gt; &lt;LBRACE&gt; property &lt;SEMI&gt; property &lt;SEMI&gt;
( property &lt;SEMI&gt; )*
( option_block )?
( event )* &lt;RBRACE&gt;
data_operation :=
&lt;DATA_OPERATION&gt; id &lt;LBRACE&gt; ( option_block )? sql_block &lt;RBRACE&gt;
/** First level constructs. */
statement := ( simple_statement &lt;SEMI&gt; | compound_statement )
simple_statement :=
( property_stmt | object_key | reference_key |
unique_key | aggressive_load | join_stmt )
compound_statement :=
/** Simple statements */
property_stmt := property
( event | option_block )
190
Appendix D. PDL Syntax
property :=
( &lt;IMMEDIATE&gt; )?
( ( &lt;VERSIONED&gt; | &lt;UNVERSIONED&gt; ) )?
( &lt;UNIQUE&gt; )?
( ( &lt;COMPONENT&gt; | &lt;COMPOSITE&gt; ) )?
type ( multiplicity )? id
( &lt;EQ&gt; ( column | join_path ) )?
multiplicity := &lt;LBRACKET&gt; integer &lt;DOT&gt; &lt;DOT&gt; ( id | integer ) &lt;RBRACKET&gt;
object_key := &lt;OBJECTKEY&gt; &lt;LPAREN&gt; id ( &lt;COMMA&gt; id )* &lt;RPAREN&gt;
reference_key := &lt;REFERENCEKEY&gt; &lt;LPAREN&gt; column &lt;RPAREN&gt;
unique_key := &lt;UNIQUE&gt; &lt;LPAREN&gt; id ( &lt;COMMA&gt; id )* &lt;RPAREN&gt;
aggressive_load := &lt;AGGRESSIVE&gt; &lt;LPAREN&gt; path ( &lt;COMMA&gt; path )* &lt;RPAREN&gt;
join_stmt := join_path
/** Compound statements */
event :=
( ( ( &lt;INSERT&gt; | &lt;UPDATE&gt; | &lt;DELETE&gt; ) |
( ( &lt;ADD&gt; | &lt;REMOVE&gt; | &lt;CLEAR&gt; ) ( id )? ) |
( &lt;RETRIEVE&gt; ( &lt;ALL&gt; | &lt;ATTRIBUTES&gt; | id )? ) )
&lt;LBRACE&gt; ( sql_block | &lt;SUPER&gt; &lt;SEMI&gt; )*
&lt;RBRACE&gt; | sql_block )
sql_block :=
( &lt;CALL&gt; | &lt;DO&gt; ) &lt;SQL&gt;
( &lt;MAP&gt; &lt;LBRACE&gt; ( mapStatement &lt;SEMI&gt; )+ &lt;RBRACE&gt; )?
mapStatement := ( binding | mapping )
binding := path &lt;COLON&gt; db_type
mapping := path &lt;EQ&gt; path
option_block := &lt;OPTIONS&gt; &lt;LBRACE&gt; ( option &lt;SEMI&gt; )+ &lt;RBRACE&gt;
option := id &lt;EQ&gt; optionValue
optionValue := &lt;TRUE&gt; | &lt;FALSE&gt; | &lt;STRINGLIT&gt;
/** Shared definitions */
join_path := join ( &lt;COMMA&gt; join )*
join := &lt;JOIN&gt; column &lt;TO&gt; column
column := id &lt;DOT&gt; id ( db_type )?
db_type := id ( &lt;LPAREN&gt; integer ( &lt;COMMA&gt; integer )? &lt;RPAREN&gt; )?
type := idpath
path := idpath
javaClass := idpath
Appendix D. PDL Syntax
191
idpath := id ( &lt;DOT&gt; id )*
id := &lt;ID&gt;
integer := &lt;INT&gt;
D.2. PDL Reserved Words
D.2.1. PDL Keywords
The following list, in conjunction with the Section D.2.2 PDL Attribute Types, details all PDL reserved words. Explanations are provided where applicable. Examples of how to use almost all of
these keywords can be found in the Chapter 9 Persistence Tutorial.
D.2.1.1. Escaping PDL Keywords
Similar to most other languages, the PDL reserved words are not valid except in the context defined for
them unless they are properly escaped. For instance, naming something &quot;composite&quot; or &quot;component&quot;
will cause a compilation error because the parser found a &quot;composite&quot; token instead of an &quot;id&quot; token.
The desire to use keywords as well as legal SQL identifiers that would not otherwise be allowed in
PDL (such as ’#’) has prompted the ability to escape special characters and words. In order to use a
reserved word or character in a PDL identifier, it is necessary to precede the character with a ’\’. For
example:
object type StereoReceiver {
...
String[1..1] serial\# = stereo_receiver.serial\#;
String[0..1] \unique = stereo_receiver.unique_column VARCHAR(100);
Component[0..1] \component = join stereo_receiver.component_id
to components.component_id;
...
}
D.2.1.2. Reserved Words
Reserved Words
--------------------------------------ADAPTER
= adapter
ADD
= add
AGGRESSIVE
= aggressive &lt;WS&gt; load
ALL
= all
ASSOCIATION
= association
ATTRIBUTES
= attributes
CALL
= do &lt;WS&gt; call
CLASS
= class
CLEAR
= clear
COMPONENT
= component
COMPOSITE
= composite
DATA_OPERATION = data &lt;WS&gt; operation
DELETE
= delete
DO
= do
EXTENDS
= extends
FALSE
= false
FOREIGNKEY
= foreign &lt;WS&gt; key
IMMEDIATE
= immediate
192
IMPORT
INSERT
JOIN
MAP
MODEL
OBJECTKEY
OBJECTTYPE
OPTION
OPTIONS
QUERY
REFERENCEKEY
REMOVE
RETRIEVE
RETURNS
SUPER
TO
TRUE
UNIQUE
UNVERSIONED
UPDATE
VERSIONED
WS
Appendix D. PDL Syntax
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
=
import
insert
join
map
model
object &lt;WS&gt; key
object &lt;WS&gt; type
option
options
query
reference &lt;WS&gt; key
remove
retrieve
returns
super
to
true
unique
unversioned
update
versioned
([ , \t, \n, \r, \f])+
Punctuation
----------SEMI
= ;
EQ
= =
DOT
= .
COMMA
= ,
STAR
= *
LBRACE
= {
RBRACE
= }
LBRACKET = [
RBRACKET = ]
LPAREN
= (
RPAREN
= )
COLON
= :
Regular expressions
------ID
= (&lt;ESC&gt;|&lt;CH&gt;) (&lt;ESC&gt;|&lt;CH&gt;|&lt;DIGIT&gt;)*
CH
= [a-z, A-Z, _, $]
ESC
= &quot;\\&quot; ~[]
INT
= (&lt;DIGIT&gt;)+
DIGIT
= [0-9]
STRINGLIT = \&quot; ( ~[\&quot;] | \\\&quot; )* \&quot;
Special Tokens
-------------COMMENT: // (~[\n, \r])* (\n | \r | \r\n)
• add — used with associations.
The PDL file uses the add keyword, along with an association name,
to signify that a given association should be inserted into the database.
— used to signify that a Data Operation contains PL/SQL and should use a
CallableStatement to execute the block of SQL defined in the do block.
• call
• clear —
used with associations. The PDL file uses the clear keyword, along with an association
name, to signify that all associations of the given name should be deleted from the database. This
can be thought of as a &quot;remove all&quot; keyword.
Appendix D. PDL Syntax
• component
193
— this word is reserved for future use.
— used to signify a definition of a composite relationship between the current Object
Type and another Object Type. This is used in the same fashion as the association keyword.
• composite
• data operation — the keyword
used to signify the beginning of a SQL block that is used outside
of an object type. It is used for any type of data modeling language (DML) operations, such as insert,
update, delete, and PL/SQL procedure calls.
• default
— this word is reserved for future use.
• delete — used to signify the beginning
of the block of code defining the delete event (for example,
how to insert an object of the defined type).
— used to signify the beginning of a block of SQL that should be executed by the persistence
layer. This is typically used inside defined events.
• do
— the token used to represent the string data operation. This is used to signify that DML
may be executed within the code block.
• dml
— used to signify that the declared object type is a subclass of another object type. This
is similar to the Java extends keyword.
• extends
• false
— the boolean value false.
• flexfields
— this word is reserved for future use.
— used to signify a foreign key when defining the table schema. It is not currently
used in PDL files, but will be added in the future.
• foreign key
— used to signify that another ObjectType will be used by the containing object type.
For instance, for an ObjectType that extends ACSObject, the second line of the PDL file would
be import com.arsdigita.kernel.*;.
• import
• insert —
used to signify the beginning of the block of code defining the &quot;insert&quot; event (for example, how to insert an object of the defined type).
— a keyword, used in association with to, to define the way to join two database tables
together. In object types, sequences of join-to statements are defined to assist the metadata-driven
SQL system in generating the standard queries.
• join
— used to signify the beginning of the block that maps attribute names to specific database
columns.
• map
— used to define the namespace for the given object type. This is analogous to the package
definition in Java.
• model
• object key
— used to uniquely identify a single object of the defined type. For instance, for an
ACSObject, the object key is id.
— used to define the name of the given object type. This is analogous to the Class
definition in Java.
• object type
• options
or type.
• query
— used to signify that the following PDL block is a group of options for the given query
— used to signify the beginning of a named SQL block that is used outside of the standard
create, retrieve, update, and delete blocks. It is typically followed by a name (the name is
used to identify it in the Java code) and then the block of SQL to execute and the mapping of the
block to attribute names.
— the keyword used to specify the column that holds an object type’s object id
locally. In metadata-driven SQL, this information is used to join against the super object type tables.
• reference key
— used with associations. The PDL file uses the remove keyword, along with an association name, to signify that a given association should be deleted from the database.
• remove
194
Appendix D. PDL Syntax
• retrieve —
used to signify the beginning of the block of code defining the retrieve event. One
example of this would be a code block specifying how to retrieve an object of the defined type. It
can also be used with the keyword all to retrieve all objects of the defined type.
• returns
— used to signify that a definition returns something. One example is returns within a
Data Query definition. In that case, it is used as an optional parameter in conjunction with two
values to indicate the number of rows that may be returned by the given query.
— used to designate calling the same named method within the parent category. This can
only be used when the object type extends another object type and is typically used within SQL
event declarations.
• super
— a keyword, used in association with join, to define the way to join two database tables
together. In object types, sequences of join-to statements are defined to assist the metadata-driven
SQL system in generating the standard queries.
• to
• true
— the boolean value true.
— signifies that only one object type may have a given value for the attribute or combination of attributes. It also tells the DDL Generator to create a unique constraint.
• unique
• unversioned —
means that the versioning service should not version this attribute.
— the keyword used to signify the beginning of the block of code defining the update
event (for example, how to update an object of the defined type).
• update
— when used in front of an object type, this keyword tells the versioning service to
version all instances of this type; when used in front of a compound attribute, this keyword tells
the versioning service to version this attribute, even though it would not normally be versioned
otherwise.
• versioned
• White Space
— the token used to signify spaces. That is, &quot; &quot;, &quot;\t&quot;, &quot;\n&quot;, &quot;\r&quot;, or &quot;\f&quot;.
D.2.2. PDL Attribute Types
The PDL Attribute Types are the allowed Java types for attributes defined in PDL. Therefore, every
type seen here is the Java type returned by the persistence system.
BigInteger
BigDecimal
Boolean
Byte
Character
Date
Double
Float
Integer
Long
Short
String // This should be used for both Strings and Clobs.
Blob
// This actually returns a Byte[] and will be deprecated once
// the PDL compiler supports arrays.
D.3. PDL and SQL Used in the Tutorial
This section provides two examples, one each of SQL and PDL usage. These can be used as quick
references to the context of every SQL and PDL example throughout the WAF Developer Guide. The
PDL usage is first in Example D-1, with the SQL usage second in the Example D-2.
Appendix D. PDL Syntax
model tutorial;
object type Publication {
BigDecimal id = publications.publication_id INTEGER;
String name = publications.name VARCHAR(400);
object key (id);
}
object type Magazine extends Publication {
// we need to specify the size of the String attribute so we know
// whether it is actually a String or if it is really a Clob
String issueNumber = magazines.issue_number VARCHAR(30);
// notice that because it extends Publication, there is not an
// explicitly &quot;object key&quot; declaration. Rather, there is
// a &quot;reference key&quot; declaration and &quot;id&quot; is not defined
// as one of the attributes
reference key (magazines.magazine_id);
}
object type Article {
BigDecimal id = articles.title INTEGER;
String title = articles.title VARCHAR(30);
object key (articles.article_id);
}
// this is an &quot;association block&quot; associating &quot;articles&quot; and &quot;magazines&quot;
association {
// note that the Attribute Type is an Object Type (Article)
// and not a standard Java Type. Also notice the order of the
// join path and see the note below.
Article[0..n] articles = join magazines.magazine_id
to magazine_article_map.magazine_id,
join magazine_article_map.article_id
to articles.article_id;
Magazine[0..n] magazines = join articles.article_id
to magazine_article_map.article_id,
join magazine_article_map.magazine_id
to magazines.magazine_id;
// the next line is the Link Attribute
BigDecimal pageNumber = magazine_article_map.page_number INTEGER;
}
object type Paragraph {
BigDecimal id = paragraphs.paragraph_id INTEGER;
String text = paragraphs.text CLOB;
object key (paragraphs.paragraph_id);
}
association {
Article[1..1] articles = join paragraphs.article_id
to articles.article_id;
// notice the composite keyword indicates that if the article does
// not exist then the paragraph also does not exist
composite Paragraph[0..n] paragraphs = join articles.article_id
to paragraphs.article_id;
}
195
196
Appendix D. PDL Syntax
object type screenName {
BigDecimal id = screen_names.name_id INTEGER;
String screenName = screen_names.screen_name VARCHAR(700);
Blob screenIcon = screen_names.screen_icon BLOB;
object key (id);
}
object type Author {
BigInteger[1..1] id = authors.author_id INTEGER;
String[1..1] firstName = author.first_name VARCHAR(700);
String[1..1] lastName = author.last_name VARCHAR(700);
Blob[0..1] portrait = authors.portrait BLOB;
// notice the use of a join path to allow the events for the
// Role Reference to be automatically created.
ScreenName[0..1] screenName =
join authors.screen_name_id to screen_names.name_id;
object key (id);
}
query paragraphMagazines {
BigDecimal magazineID;
BigDecimal paragraphID;
Integer issueNumber;
String text;
do {
select m.magazine_id, p.paragraph_id, issue_number, text
from magazines m, a, magazine_article_map ma, paragraphs p
where ma.magazine_id = m.magazine_id
and p.article_id = ma.article_id
} map {
magazineID = m.magazine_id;
paragraphID = p.paragraph_id;
issueNumber = m.issue_number;
text = p.text;
}
}
query MagazineToAuthorMapping {
// the next two lines are declaring that objects will be returned
Magazine magazine;
Author author;
options {
WRAP_QUERIES = false;
}
do {
select publications.name, issue_number, publication_id,
authors.first_name, authors.last_name, author_id
from magazines, publications, articles, authors,
magazine_article_map, article_author_map
where publications.publication_id =
magazines.magazine_id
and magazine_article_map.magazine_id =
magazines.magazine_id
Appendix D. PDL Syntax
and magazine_article_map.article_id =
article_author_map.article_id
and article_author_map.author_id = authors.author_id
} map {
// here we map the attributes of the objects
// to columns returned by the query.
magazine.name = publications.name;
magazine.issueNumber = magazines.issue_number;
magazine.id = publications.publication_id;
author.authorID = authors.author_id;
author.firstName = authors.first_name;
author.lastName = authors.last_name;
}
}
query MagazineWithMaxID {
BigDecimal magazineID;
do {
select max(magazine_id) as magazine_id from magazines
} map {
magazineID = magazines.magazine_id;
}
}
data operation createMagazine {
do {
insert into magazine_article_map (magazine_id, article_id)
select :magazineID, article_id from articles where not exists
(select 1 from magazine_article_map
where magazine_article_map.article_id = articles.article_id)
}
}
data operation DataOperationWithPLSQLAndArgs {
// the &quot;call&quot; keyword after the &quot;do&quot; indicates that the following
// is actually a piece of PL/SQL. The system then uses a
// java.sql.CallableStatement to execute it instead of only a
// java.sql.PreparedStatement.
do call {
myPLSQLProc(:title)
}
}
data operation DataOperationProcWithInOut {
do call {
DataOperationProcWithInOut(:newID, :copiedID)
} map {
newID : INTEGER;
copiedID : INTEGER;
}
}
query DataOperationWithPLSQLAndArgsAndReturnInPDL {
do call {
:title = DataQueryPLSQLFunction(:articleID)
} map {
title : VARCHAR(700);
articleID : Integer;
}
}
query myDataQuery {
197
198
Appendix D. PDL Syntax
BigDecimal articleID;
options {
WRAP_QUERIES = false;
}
do {
select max(article_id) from articles
} map {
articleID = articles.article_id;
}
}
query UsersGroups {
String firstName;
String lastName;
String groupName;
do{
select *
from users, groups, membership
where users.user_id = membership.member_id
and membership.group_id = groups.group_id
} map {
firstName=users.first_name;
lastName=users.last_name;
groupName=groups.group_name;
}
}
query retrieveArticlesBasedOnAuthor {
BigDecimal authorID;
do {
select article_id
from authors, author_article_map
where authors.author_id = author_article_map.author_id
and lower(last_name) like :lastName || ’%’
} map {
authorID = authors.author_id;
}
}
query retrieveSelectedArticles {
BigDecimal articleID;
String title;
do {
select article_id, title from articles
} map {
articleID = articles.article_id;
title = articles.title;
}
}
query CategoryFamily {
Integer level;
BigDecimal categoryID;
String name;
String description;
Boolean isEnabled;
do {
select l, c.category_id, c.name, c.description, c.enabled_p
from (select level l, related_category_id
from (select related_category_id, category_id
from cat_category_category_map
Appendix D. PDL Syntax
where relation_type = :relationType)
connect by prior related_category_id = category_id
start with category_id = :categoryID) m,
cat_categories c
where c.category_id = m.related_category_id
} map {
level = m.l;
categoryID = c.category_id;
name = c.name;
description = c.description;
isEnabled = c.enabled_p;
}
}
Example D-1. Usage Reference for PDL
create table publications (
publication_id
integer
constraint publications_pub_id_nn
not null
constraint publications_pub_id_pk
primary key,
name
varchar(400)
constraint publications_pub_id_nn
not null
);
create table magazines (
magazine_id
integer
constraint magazines_magazine_id_fk
references publications
constraint magazines_magazine_id_pk
primary key,
issue_number
varchar(30)
);
create table articles (
article_id
integer
constraint articles_article_id_pk
primary key
constraint articles_article_id_nn
not null
title
varchar(700)
constraint articles_title
);
create table magazine_article_map (
magazine_id
integer
constraint mag_article_map_mag_id_nn
not null
constraint mag_article_map_mag_id_fk
references magazines,
article_id
integer
constraint mag_article_map_article_id_fk
references articles
constraint mag_article_map_article_id_nn
not null,
page_number
integer
);
199
200
Appendix D. PDL Syntax
create table paragraphs (
paragraph_id
integer
constraint paragraphs_paragraph_id_pk
primary key
constraint paragraphs_paragraph_id_nn
not null,
text
clob,
article_id
integer
constraint paragraphs_article_id_fk
references articles
constraint paragraphs_article_id_nn
not null
);
create table authors (
author_id
integer
constraint authors_author_id_nn
not null
constraint authors_author_id_pk
primary key,
last_name
varchar(700)
constraint authors_name_nn
not null,
first_name
varchar(700)
constraint authors_name_nn
not null,
portrait
blob,
screen_name_id
integer references screen_names
);
create table screen_names (
name_id
integer primary key,
screen_name
varchar(700) not null,
screen_icon
blob
);
create or replace function myPLSQLProc(v_priority in integer)
as
begin
insert into magazines (magazine_id, title)
select nvl(max(magazine_id), 0) + 1, :title from magazine_id;
end;
/
show errors
create or replace procedure DataOperationProcWithInOut(
v_new_id IN Integer,
v_copied_id OUT Integer)
as
begin
select max(article_id) into v_copied_id from articles;
insert into articles (article_id, title)
select v_new_id, title from articles
where article_id = v_copied_id;
insert into article_author_map (article_id, author_id)
select v_new_id, author_id from article_author_map
where article_id = v_copied_id;
end;
/
show errors
create or replace function
Appendix D. PDL Syntax
DataQueryPLSQLFunction(v_article_id in integer)
return number
is
v_title varchar(700);
begin
select title into v_title from articles
where article_id = v_article_id;
return v_title;
end;
/
show errors
Example D-2. Usage Reference for SQL
201
202
Appendix D. PDL Syntax
Persistence Glossary
The terms used by the persistence system are largely based upon the Unified Modeling Language
(UML) terminology. For background information, please consult the UML documentation at
http://www.rational.com/uml/.
Association
Associations are bi-directional semantic connections. Put another way, they represent the relationship between two separate objects (UML Classes). Objects within an association are completely independent, though they may be linked together. Data may be passed in either or both
directions, and more than one association may exist between two classes. In UML diagrams,
associations are represented as links (lines between the two objects).
An example of an association is the relationship between a user and a group. From the level
of object modeling, the two classes involved are User and Group and there is a many-to-many
association between them. In this case, the association is one of membership. That is, a user &quot;is
a member of&quot; a group.
See Also: Composite.
Attributes
Attributes are data fields that represent some property of the containing object that is shared by
all instances of the object’s class. Attributes normally have names (e.g., &quot;Address&quot;) and Types
(e.g., &quot;String&quot; or &quot;Boolean&quot;). An example of this would be the &quot;Address&quot; of a &quot;User.&quot;
See Also: Property.
Composite
A Composite Relationship (also known as a &quot;Composition&quot;) is a special kind of association in
which one class cannot exist without another. That is, the object strongly owns its parts and if
the object is deleted, its parts must also be deleted. The multiplicity at the parent object end
must be 1..1 or 0..1. An example of a composite relationship is a key with a keyboard. The key
is useless without the keyboard; if you remove the keyboard, you are also removing the key.
Composite associations are useful for modeling relationships between objects where a contained
object cannot exist outside its container object.
An example specific to the WAF is the composition between Parties and WAF Objects. A Party
cannot exist without the corresponding WAF Object. If the WAF Object is deleted, the Party must
also be deleted. The multiplicity holds because each Party has exactly one related WAF Object.
See Also: Association.
Derived Associations
Derived Associations are exactly like Associations, except that they have one or more levels of
indirection. That is, if A is associated with B, and B is associated with C, then A has a Derived
Association with C.
See Also: Association.
Data Object
A Data Object is any persistent entity within a relational database that is exposed to the applications as an object. An example is a row within the &quot;users&quot; table. It is important to realize that
Data Objects are not the same as Domain Objects, and that they actually have a many-to-many
relationship. See Section 9.2 Beginning With Data Objects and for more information.
See Also: Domain Object.
204
Persistence Glossary
Domain Object
Domain objects are not part of the persistence layer, but since they are the most common way
to access a Data Object (which is part of the persistence layer), it is useful to discuss them here.
Domain objects contain logic particular to a business domain, such as managing users or credit
cards. This logic operates over a persistent data object that contains the state necessary to implement the domain-specific logic. Domain objects contain the application logic specific to the
domain that requires representing persistent state. It is important to realize that Domain Objects
are not the same as Data Objects. Domain Objects and Data Objects have a many-to-many relationship with each other. See the Section 10.2 Domain Objects Tutorial for more information
See Also: Data Object.
Filter
Filters are used to allow developers to restrict the results returned by a Data Query or the
results represented in a Data Association or Data Collection.
Join Element
A Join Element is a single part of the larger Join Path. It is used to indicate how two tables can
be joined to each other. In the following example, there are 4 Join Elements that make up 2 Join
Paths. The first Join Element is in the form join foo and the second one is in the form of to
bar.
association {
Article[0..n] articles = join magazines.magazine_id
to magazine_article_map.magazine_id,
join magazine_article_map.article_id
to articles.article_id;
Magazine[0..n] magazines = join articles.article_id
to magazine_article_map.article_id,
join magazine_article_map.magazine_id
to magazines.magazine_id;
}
See Also: Join Path.
Join Path
A Join Path is the collection of Join Elements seperated by commas and indicate how to join
tables to each other. They are typically used within associations to indicate how the objects
within the database are related.
In the following example of an association between Articles and Magazines, there are two Join
Paths; the first one is in bold and the second is in italics.
association {
Article[0..n] articles = join magazines.magazine_id
to magazine_article_map.magazine_id,
join magazine_article_map.article_id
to articles.article_id;
Magazine[0..n] magazines = join articles.article_id
to magazine_article_map.article_id,
join magazine_article_map.magazine_id
to magazines.magazine_id;
}
Persistence Glossary
205
Link Attributes
A Link is the path from one object to another. Associations are types of links. A Link Attribute
is a property of this link. For instance, if a developer wanted to know when the link was created,
he could store the creationDate as a Link Attribute.
See Section 9.3.4 Link Attributes and Section 9.8 Link Attributes.
Link Role
See: Roles
Multiplicity
Multiplicity refers to a set of values (all non-negative integers, plus infinity) that can be used to
describe cardinality. PDL uses a Multiplicity to specify the relationship between objects within
Associations. Specifically, it can be used to answer the question, &quot;given an object of type A, what
is the range of number of objects of type B that can be related to A?&quot; The syntax used is &quot;[#..#]&quot;
where # is either &quot;0&quot;, &quot;1&quot;, or &quot;n&quot;. The valid multiplicities are &quot;[0..1]&quot; (there may or may not be a
single associated object), &quot;[0..n]&quot; (there may be zero to n associated objects), and &quot;[1..1]&quot; (there
is always exactly one object related to the given object). The Multiplicities with an upper bound
of &quot;n&quot; are typically used when there is a mapping table involved. The Multiplicity of &quot;[1..1]&quot; is
typically used when there is a non-null, single column in the table referencing another table. If
no multiplicity is specified, &quot;[0..1]&quot; is used as the default.
Property
Within the persistence system, Property is used as the global term to describe either an attribute
or an association of an Object Type.
Reference Key
The Reference Key provides the Metadata Driven SQL system information about how to join
the current Object Type with its super Object Type. In a standard Object Type that does not
extend anything, an Object Key is declared to uniquely identify the object within the tables. If
an Object Type extends another Object Type, a Reference Key is used instead of an Object Key.
This Reference Key holds information about how the table of the child type can be joined with
the table of the super type. For an example, see Section 9.2.6 Object Type Inheritance.
If the Object Key of the parent is keyed off of multiple rows, the columns in the reference key
must appear in the order in which they should be joined. For instance, the definitions below will
produce the join syntax that follows them (remove the &quot;\&quot; and make it all one line).
D
E
D
E
model tutorial;
object type FirstObjectType {
Attributes defined here
object key (object_id_one, object_id_two);
}
object type SecondObjectType extends FirstObjectType {
Attributes defined here
reference key (secondtable.second_object_id_one, \
secondtable.second_object_id_two);
}
The above PDL would produce SQL join code similar to the following:
206
Persistence Glossary
F
G
select code and tables here
where secondtable.second_object_id_one = firsttable.object_id_one
and secondtable.second_object_id_two = firsttable.object_id_two
See Also: Object Key.
Roles
Roles describe how one class is associated with another. One or both classes in the association
may have roles. For example, a User has a &quot;Member&quot; role for the group (that is, a user is a
member of a group).
See Also: Role Reference.
Role Reference
Role Reference is the term used to describe an object type’s reference to another object type. It
is similar to having an attribute with an Object Type modifier instead of a Java type. See Section
9.3.3 Role References and Section 9.3.5 Using Java to Access Associations for more information.
See Also: Property.
Metadata Driven SQL (MDSQL)
Metadata Driven SQL is the term used to describe SQL that is automatically generated by the
persistence layer. The persistence layer is able to generate statements to perform insert, update,
and delete, and it selects from the database if it is given enough information about the object
(e.g., information about how attributes map to database columns and how tables can be joined
together). In addition, it is able to use the object type metadata to generate DDL statements that
can be used to create an update the actual table definitions.
Object Key
The Object Key allows the persistence system to uniquely identify a particular Data Object for
a given Object Type. Specifically, the Object Key column(s) of an Object type is similar to the
&quot;primary key&quot; of a database table.
If a particular object has a multi-key primary key, it should have a multi-key Object Key as
well. To do this, you can simply separate the attributes by commas. For instance, for a mapping table whose primary key contains the columns object_id (whose attribute is id) and
site_node_id (whose attribute is siteNodeID), the object key would look like object key
(id, siteNodeID). This is not a strong example, however, because in the common case mapping tables should not be represented as object types. Rather, they should be used in join paths
when defining associations.
For more information, see the Section 9.2.3.3 Object Key section of the PDL tutorial.
See Also: Reference Key.
PDL
See: Persistence Definition Language (PDL)
Persistence Definition Language (PDL)
The Persistence Definition Language has been created to provide developers with a syntax to
specify data objects, their associations, and how the information is stored in the database. The
files specified in PDL and SQL are the only files that contain actual SQL and thus are the only
files that must be changed when porting the system to a new database.
Persistence Glossary
207
UML Class
A UML Class is a description of a set of objects that share the same attributes, operations, and
relationships. A UML Class is almost identical to a Java class.
208
Persistence Glossary
Index
(See master pages)
building
with Eclipse, 40
A
acronyms
presentation, 19
ACSObject
base permissioning class, 11
API
mail, 16
appenders
custom WAF, 47
logging, 47
Application
BaseServlet defined, 31
properties, 31
applications
determining Locale, 165
dispatcher defined, 32
notes
PropertyResourceBundle, 166
ResourceBundle, 166
overview, 6
Servlet, mapping to, 32
WAF base class, 31
architecture
overview, 2
Association, 203
Association Block
Example, 70
Composite
Example, 71
Defining, 70
Java
Example, 73
Attribute, 203
auditing
service concept, 13
B
BaseServlet
Application, definition of, 31
Bebop
and globalization, 169
handling HTML, 153
JSP integration, 28
master pages, 155
Presentation, 25
Usage, 26
XSLT, using with, 153
Binding Parameters
Examples, 79
see Paramter Binding, 86
boilerplate
C
categorization
service concept, 13
taxonomies, 13
ccm tool usage, 60
upgrade, 60
Composite, 203
Composite Associations
Java
Example, 74
concept of
group, 11
party, 11
permissions, 11
user, 11
configuration
Eclipse, 38
conventions
document, i
CSS
Presentation Conventions, 20
D
Data Collection
Creating, 68
data layer
overview, 3
Data Object, 203
API, 66
Creating, 68
Retrieving, 68
data objects
overview, 3
Data Operation
Example, 76
Arbitrary DML, 77
PL/SQL, 77
Data Query
Example, 74
Creating Data Objects, 75
Retrieve, 74
Data Storage layer
overview, 3
Database
Persistence, 9
debuggers
(See debugging)
Debugging, 90
interface, 36
210
logging concepts, 42
problems with System.out.println(), 43
with Eclipse, 41
with log4j, 43
deploying
with Eclipse, 40
Derived Associations, 203
developer
education, 35
prerequisites, 35
Developer Support application
accessing, 37
features, 37
Developer Support application
development, 36
development
Developer Support application, 36
environment, 35
tools, 35
Domain APIs
Persistence, 10
domain layer
overview, 3
Domain Object, 204
creating, 106
Dynamic DDL Generation, 89
E
Eclipse
building with, 40
configuration, 38
debugging function, 41
deploying with, 40
installation, 38
Perforce setup, 40
preferences, 38
project configuration, 39
tools, 38
validating setup, 42
education
developer, 35
email messages
(See mail service)
environment
development, 35
Exceptions
conventions, 187
logging the, 44
F
Filter, 204
Filtering
Examples, 79
How-To, 80
Complex, 81
Simple, 80
formbuilder
implementing, 161
service concept, 14
forms
(See formbuilder)
building of, 14
G
g11n
(See globalization)
globalization
and Bebop, 169
implementing, 165
localizing stylesheets, 170
service concept, 15
GlobalizedMessage
cautionary note, 167
grammar
PDL, 189
grouping
localization resources, 167
groups
(See users, groups and parties)
H
HTML
handling using Bebop, 153
mail
(See rich text messages)
I
infrastructure
logging, 6
installation
Eclipse, 38
211
J
Java coding standards, 187
references, 188
JavaServer Pages
(See JSP)
Join Element, 204
Join Path, 204
Join Paths, 89
JSP
Bebop integration, 28
dynamic pages, 29
extending BaseJSP, 31
Presentation, 25
static pages, 29
manipulating in runtime, 45
M
mail
(See mail service)
API, 16
service concept, 16
mail attachments
(See mail service)
mail service
K
kernel
overview, 3
resources, 12
users, groups and parties defined, 11
L
language
determining local, 165
language localization
(See globalization)
Lifecycle
Request, 27
UI, 27
Link Attributes, 92, 205
Example, 72
Link Role
(See Roles)
Locale
and PropertyResourceBundle, 166
and ResourceBundle, 166
application determination, 165
localization
grouping resources, 166
localization data
grouping, 167
localization resources
representing, 167
log4j
using for debugging, 43
log4j logging application, 43
logging
and debugging, 42
and performance, 48
appenders, 47
exceptions, 44
interface, 36
attachments, 170
sending using web applications, 170
Mapping
Object Modeling, 9
Relational Modeling, 9
markup text
(See pre-formatted text)
master pages
handling with Bebop, 155
shared layout
varying shared layout, 158
messaging
service concept, 16
Meta-Data Driven SQL, 206
Model
Object Type, 65
Multiplicity
Defined, 205
N
Naming
conventions, 187
notification
compared to mail, 17
service concept, 17
212
O
Object
Persistence, 9
Object Key
Defined, 206
Example, 65
Object Type
Inheritance, 69
Model, 65
Object-Relational
Mapping, 9
Ordering
Examples, 79
How-To, 85
output streams
problem with buffered, 47
P
Parameter Binding
How-To, 86
parties
(See users, groups and parties)
PDL
(See Persistence Definition Language (PDL))
Defined, 9
grammar, 189
PDL Keywords - escaping
reserved words, 191
PDL Reserved Words - List, 191
Perforce
and Eclipse, 40
performance
and logging, 48
permissions
ACSObject, 11
concept of, 11
UI tutorial, 160
Persistence
Database, 9
Domain APIs, 10
Object, 9
Overview, 9
PDL, 9
Persistence Definition Language, 9
Persistence Definition Language (PDL)
reserved words, 191
Persistence Definition Language (PDL), 206
File Definition, 64
persistence metadata
overview, 3
PL/SQL
Defining, 77
Functions
Using, 79
Procedures
Using, 77
portal
service concept, 17
pre-formatted text
handling using Bebop, 153
preferences
Eclipse, 38
prerequisites
developer, 35
presentation
acronyms, 19
Bebop, 25
CSS, 20
JSP, 25
site node, tutorial, 20
standards of, 19
XSL, 20
XSLT tutorial, 20
presentation layer
overview, 3
project configuration
Eclipse, 39
properties of an
Application, 31
Property
Defined, 205
PropertyResourceBundle
notes application, 166
R
Reference Key
Defined, 205
References
Java coding standards, 188
Request
Lifecycle, 27
Request context, 31
ResourceBundle
notes application, 166
resources
kernel base class, 12
rich text messages
and mail service, 170
Role Reference
Defined, 206
Java
Example, 74
PDL
Example, 72
Roles, 206
runtime debugging
logging level manipulation, 45
with Eclipse, 41
213
S
U
search
service concept, 17
service
auditing, concepts of, 13
categorization, concepts of, 13
formbuilder, concepts of, 14
globalization, concepts of, 15
mail, concepts of, 16
messaging, concepts of, 16
notification, concepts of, 17
search, concepts of, 17
versioning, concepts of, 18
workflow, concepts of, 18
services
portal, concept of, 17
Servlet
Applications, mapping to, 32
Session
Management, 10
shared layout
(See master pages)
standards
presentation, 19
structured Data
parsing, 19
stylesheets
(See XSLT)
and globalization, 165
and Locale, 170
localizing using Bebop, 170
Swing
(See Bebop)
UI, 160
(See Also user-interface)
Lifecycle, 27
UI Components
Web-based, 25
UML Class, 207
upgrading
scripts, 60
using ccm command, 60
user Locale
globalization, utilizing, 165
user requests
connecting to Applications, 32
user-interface
permissions tutorial, 160
users
(See users, groups and parties)
users, groups and parties
concept of, 11
Using
Bebop, 26
V
validating
Eclipse setup, 42
versioning
service concept, 18
T
taxonomy
setup with categorization, 13
templates
website
(See master pages)
toolchain
(See tools)
tools
Developer Support application, 36
development, 35
Eclipse, 38
and Perforce, 40
Transaction
Management, 10
Transaction management, 31, 90
translation
identifying items to translate, 167
W
WAF
basic configuration, 3
developing on, 35
warning
buffered streams, 47
Web Applications
concept of, 31
Web-based
UI Components, 25
website templates
(See master pages)
workflow
service concept, 18
214
X
XSL
Presentation Conventions, 20
XSLT
Bebop, using with, 153
globalization, 170
implementing, 153
overriding default stylesheet, 159
using with WAF, 20
Colophon
The Red Hat Applications manuals are written in DocBook SGML v4.1 format. The HTML and PDF
formats are produced using custom DSSSL stylesheets and custom jade wrapper scripts. The DocBook
SGML files are primarily written in Emacs with the help of PSGML mode; additional authoring and
editing has been done with vi using macros and key mappings.
Garrett LeSage created the admonition graphics (note, tip, important, caution, and warning). They
may be freely redistributed with the Red Hat documentation.
The Red Hat Applications Product Documentation Team is:
Karsten Wade — Primary Writer/Maintainer of Red Hat Applications documentation for Red Hat
WAF and Red Hat CMS, for example the Red Hat Web Application Framework Installation Guide,
the Red Hat Web Application Framework Developer Guide, and the Red Hat Content Management
System Deployment Guide.
Char James-Tanny — Writer of the Red Hat Content Management System Administrator Guide and
the Red Hat Content Management System User Guide.
The Red Hat Applications Product Development Team made significant contributions to the constructing, authoring, and editing of the entire line of Red Hat Applications documentation.
•
Archit Shah
•
Bryan Che
•
Dan Berrange
•
Dennis Gregorovic
•
Jon Orris
•
Jim Parsons
•
Justin Ross
•
Rafael Schloming
•
Richard Li
•
Richard Su
•
Scott Seago
•
Vadim Nasardinov
None of the Red Hat Applications documentation would be possible without the extremely able assistance of the Red Hat Documentation Technical Lead, John Ha.
The Red Hat Applications documentation has descended from guides originally written for ArsDigita.
The words, images, and ideas live on from these contributors:
•
Bob Donald
•
Pete Su
216
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