An introduction to creating Java EE applications in September, 2010

An introduction to creating Java EE applications in September, 2010
An introduction to creating
Java EE applications in
Rational Application Developer Version 8.0
September, 2010
© Copyright IBM Corporation 2010.
1
Overview
Java Enterprise applications (Java EE applications) are applications that conform
to the Java Platform, Enterprise Edition (Java EE) specification. Prior to Java EE,
the specification name was Java 2 Platform, Enterprise Edition (J2EE). The term
Java EE includes Java EE and J2EE specifications.
In the Java EE specifications, programming requirements have been
streamlined, and XML deployment descriptors are optional. Instead, you can
specify many details of assembly and deployment with Java annotations. Java
EE provides default values in many situations so explicitly specification of these
values are not required.
In Rational Application Developer, code validation, content assistance, Quick
Fixes, and refactoring simplify working with your code. Code validators check
your projects for errors. When an error is found, you can double-click it in the
Problems view in the workbench to go to the error location. For some error types,
you can use a Quick Fix to correct the error automatically. For both Java source
and Java annotations, you can rely on content assistance to simplify your
programming task. When you refactor source code, the tools automatically
update the associated metadata.
For additional information about Java EE, see the official specification: JSR 316:
Java Platform, Enterprise Edition 6 (Java EE 6) Specification.
What is Java EE
Using the Java™ Platform, Enterprise Edition (Java EE) architecture, you can
build distributed Web and enterprise applications. This architecture helps you
focus on presentation and application issues, rather than on systems issues.
You can use the Java EE tools and features to create applications that are
structured around modules with different purposes, such as Web sites and
Enterprise Java beans (EJB) applications. When you use EJB 3.1 components,
you can create a distributed, secure application with transactional support. When
you develop applications that access persistent data, you can use the new Java
Persistence API (JPA). This standard simplifies the creation and use of
persistent entities, as well as adding new features. For developing presentation
logic, you can use technologies such as JavaServer Pages (JSP) or JavaServer
Faces (JSF).
Using the Java EE Platform Enterprise Edition (Java EE), you can develop
applications more quickly and conveniently than in previous versions. Java EE
significantly enhances ease of use providing
© Copyright IBM Corporation 2010.
2
•
•
•
Reduced development time
Reduced application complexity
Improved application performance
Java EE provides a simplified programming model, including the following tools:
•
•
•
•
Inline configuration with annotations, making deployment descriptors now
optional
Dependency injection, hiding resource creation, and lookup from application
code
Java persistence API (JPA) allows data management without explicit SQL or
JDBC
Use of plain old Java objects (POJOs) for Enterprise Java beans and Web
services
Java EE provides simplified packaging rules for enterprise applications:
•
•
•
•
•
•
•
•
•
Web applications use .WAR files
Resource adapters use RAR files
Enterprise applications use .EAR files
The lib directory contains shared .JAR files
A .JAR file can be specified in the application.xml of the EAR either as an
application client or as an EJB module
A .JAR file not specified by the application.xml of the EAR is defined as
follows:
• A .JAR file with an application-client.xml implies an application client
• A .JAR file with an ejb-jar.xml implies an EJB module
• A .JAR file with META-INF/MANIFEST.MF specified Main-Class implies
an application client
• A .JAR file with any @Stateless, @Stateful, or @MessageDriven
annotations implies an EJB application
A .JAR file with Main-Class implies an application client
A .JAR file with @Stateless annotation implies an EJB application
Many simple applications no longer require deployment descriptors, including
• EJB applications (.JAR files)
• Web applications that use JSP technology only
• Application clients
• Enterprise applications (.EAR files)
Java EE provides simplified resource access using dependency injection:
•
In the Dependency Injection pattern, an external entity automatically supplies
an object's dependencies. The object need not request these resources
© Copyright IBM Corporation 2010.
3
•
•
explicitly.
In Java EE, dependency injection can be applied to all resources that a
component needs. Creation and lookup of resources are hidden from
application code.
Dependency injection can be applied throughout Java EE technology:
• EJB containers
• Web containers
• Clients
• Web services
Creating and configuring Java EE modules using
annotations
The goal of Java™ EE 6 platform development is to minimize the number of
artifacts that you have to create and maintain, thereby simplifying the
development process. Java EE supports the injection of annotations into your
source code, so that you can embed resources, dependencies, services, and
lifecycle notifications in your source code, without having to maintain these
artifacts elsewhere.
An annotation is a modifier or metadata tag that provides additional data to Java
classes, interfaces, constructors, methods, fields, parameters, and local
variables. Annotations replace boilerplate code, common code that is required by
certain applications. For example, an annotation can replace the paired interface
and implementation required for a Web service. Annotations can also replace
additional files that programs require, which are maintained separately. For
example, annotations can replace the need for a separately maintained
deployment descriptor for enterprise Java beans.
Annotations:
• Replace descriptors for most purposes
• Remove the need for marker interfaces (like java.rmi.Remote)
• Allow application settings to be visible in the component they affect
Java EE provides annotations for the following tasks, among others:
•
•
•
•
•
•
Developing Enterprise Java bean applications
Defining and using Web services
Mapping Java technology classes to XML
Mapping Java technology classes to databases
Mapping methods to operations
Specifying external dependencies
© Copyright IBM Corporation 2010.
4
•
Specifying deployment information, including security attributes
Java EE defines a number of annotations that can be injected into your source
code. To declare an annotation, you simply precede the keyword with an "at"
sign (@).
EJB 3.1 overview
You can use Rational Application Developer to develop and test enterprise
beans that conform to the distributed component architecture defined in the Sun
Microsystems Enterprise JavaBeans™ (EJB) 3.1 specification.
Using this specification, you can develop beans more simply than in the 2.1
standard. You can annotate your Java™ source code to provide information that
was previously contained in XML deployment descriptors. Using Java™
annotations allows you to create EJBs and Java Persistence Architecture (EJB
3.1) beans quickly and easily from “plain old Java objects” (POJOs). EJBs can
be created without implementing Enterprise JavaBean interfaces.
This product supports the Enterprise JavaBeans™ 2.1 and 3.1 specification
levels. All the EJB tools in the product are accessible from the Java EE
perspective in the workbench. You can create session beans (stateful or
stateless) or message-driven beans, by simply specifying the component
defining annotation in your POJO. Additional configuration for your bean can be
done by specifying additional annotations in the Java class. The Java editor
provides validation, content assistance, and QuickFixes for your EJB 3.1
annotations, as well as support for refactoring beans. For richer assistance with
the EJB 3.1 annotations, you can use the Annotations view to add or delete
annotations, and to modify the attribute values of annotations. Deployment
descriptors for your EJB 3.1 modules are optional, but can be created for
additional configuration.
Developing JPA applications
The Java™ Persistence API (JPA) defines the management of persistence and
© Copyright IBM Corporation 2010.
5
object/relational mapping within Java Enterprise Edition (Java EE) and Java
Standard Edition (Java SE) environments.
The Java Persistence API (JPA) represents a simplification of the persistence
programming model. JPA manages persistence and object/relational mapping
within the Java EE specification for Enterprise Java Beans 3.0. The JPA
specification defines the object/relational mapping within its own guidelines
instead of relying on vendor-specific mapping implementations. These features
make applications that use JPA easier to implement and manage.
JPA combines the best features from previous persistence mechanisms such as
Java Database Connectivity (JDBC) APIs, Object Relational Mapping (ORM)
frameworks, and Java Data Objects (JDO). Creating entities under JPA is as
simple as creating serializable classes. JPA supports the large data sets, data
consistency, concurrent use, and query capabilities of JDBC. Like objectrelational software and object databases, JPA allows the use of advanced
object-oriented concepts such as inheritance. JPA avoids vendor lock-in
because it does not rely on a strict specification like JDO and EJB 2.x entities.
The JPA implementation does not mandate that you migrate existing
applications. Existing EJB 2.x Container Manager Persistence applications
continue to execute without changes. JPA may not be ideal for every application,
however, for many applications it provides a better alternative to other
persistence implementations.
With the Rational Application Developer JPA tools, you can use wizards to
create and automatically initialize mappings. You can create new database
tables from existing entity classes (top-down mapping) or new entity beans from
existing database tables (bottom-up mapping). You can also use the tools to
create mappings between existing database tables and entity beans (meet-inthe-middle mapping), where names or other attributes differ. For flexibility in
designing your data access application, you can choose from a range of
mapping types. You can create mappings from several types of Java class, and
you can specify entity inheritance with several options for database design.
JPA is described in the JSR 220 EJB 3.1 specification: JSR 220: Enterprise
JavaBeans™ 3.0.
JPA architecture
The Java™ Persistence API represents a simplification of the persistence
programming model.
Data persistence, the ability to maintain data between application sessions in
some form of nonvolatile storage (such as a relational database), is crucial to
enterprise applications. Applications that are developed for this environment
© Copyright IBM Corporation 2010.
6
must either manage data persistence themselves or make use of third-party
solutions to handle database updates and retrievals. JPA provides a mechanism
for managing data persistence and object-relational mapping and functions for
the EJB 3.1 specifications.
JPA is based on the Java programming model that applies to Java EE
environments, but JPA can also function within the Java SE environment. The
JPA specification defines the object-relational mapping internally, rather than
relying on vendor-specific mapping implementations, and uses either annotations
or XML to map objects into database tables.
JPA is designed to operate both inside and outside of a Java Enterprise Edition
(Java EE) container. When you run JPA inside a container, applications can use
the container to manage the persistence. If there is no container to manage JPA,
the application must handle the persistence management itself. Applications
designed for container managed persistence cannot be used outside a
container, while applications that manage their own persistence can function
either in a container environment or a Java SE environment.
JPA also provides a query language - JPQL - that you can use to retrieve objects
without writing SQL queries specific to the database you are working with.
Java EE containers that support JPA must supply a persistence provider. A JPA
persistence provider uses the following elements to persist data in an EJB 3.1
environment:
•
Entity objects: An entity is a simple Java class that represents a row in a
database table. Entities can be concrete classes or abstract classes. They
maintain states by using properties or fields.
•
EntityManager: An EntityManager object maintains the active collection of
entity objects that are being used by the application. The EntityManager object
handles the database interaction and metadata for object-relational mappings.
An instance of an EntityManager object represents a persistence context. An
application in a container can obtain the EntityManager either through
injection into the application or by looking it up in the Java component
namespace. If the application manages its persistence, the EntityManager is
obtained from the EntityManagerFactory. The application server containers
typically supply this function, but the EntityManagerFactory is required if you
are using JPA application-managed persistence.
Note: Injection of the EntityManager is only supported for the following
artifacts:
•
EJB 3.1 session beans.
•
EJB 3.1 message-driven beans.
© Copyright IBM Corporation 2010.
7
•
Servlets, but injection is not supported in JSPs.
•
The main class of the application client.
•
EntityManagerFactory: The factory is used to create an EntityManager for
database interactions.
•
Persistence unit: A persistence unit consists of the declarative metadata that
describes the relationship of entity class objects to a relational database. The
EntityManagerFactory uses this data to create a persistence context that can
be accessed through the EntityManager.
•
Persistence context: The persistence context is the set of active instances that
the application is currently handling. The persistence context can be created
manually or through injection.
© Copyright IBM Corporation 2010.
8
Tools for Java EE development
The Rational Application Developer Java™ EE development tools enable you to
create enterprise applications including Enterprise Application projects, EJBs,
and Java Persistent API (JPA) applications.
The Java EE provides a rich set of tools to create, develop, test, debug, and
deploy enterprise applications. Some of the Java EE tools include:
•
Enterprise explorer view: The Enterprise explorer view allows you to manage
and maintain your enterprise applications in one location.
•
Annotations view: The Annotations view provides a way for you to create,
edit, browse, and generally keep track of the annotations that you use in your
applications.
© Copyright IBM Corporation 2010.
9
•
Project and object creation wizards: You can use Java EE wizards to create
enterprise applications, including Application client projects, Enterprise Java
bean projects, Connector projects, Web projects, and Web Services
applications.
•
Export and import wizards: You can import existing projects and modules into
your current project; you can use export wizards to build, package, and export
projects with a single click.
•
Code validation, content assistance, Quick Fixes, and refactoring: These
tools simplify working with your code. Code validators check your projects for
errors. When one is found, you can double-click it, in the Problems view in the
product workbench, to go to the error location. For some types of error, you
can also choose a Quick Fix, which automatically corrects the error. For both
Java™ source and Java annotations, you can rely on content assistance to
simplify your programming task. When you refactor source code, the tools
automatically update the associated metadata.
•
Tools for managing projects: The tools for Java EE allow you to manage
projects easily. To share applications outside of a version-control system, you
can import and export projects as archive files. To migrate your projects to the
current version of the Java EE specification, you can take advantage of a
migration wizard.
© Copyright IBM Corporation 2010.
10
For more information
To learn more about Java EE and Rational Application Developer, see these
resources:
•
Rational Application Developer Web site:
http://www-01.ibm.com/software/awdtools/developer/application/index.html
•
Rational Application Developer Information Center:
http://publib.boulder.ibm.com/infocenter/radhelp/v7r5/index.jsp
•
Rational Application Developer wiki:
https://www.ibm.com/developerworks/wikis/display/rad/Home
© Copyright IBM Corporation 2010.
11
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertisement