Modernizing
the Mainframe
with Java
Gregg Lippa
Senior Technical Analyst
Themis Education
Themis, Inc.
glippa@themisinc.com
Visit us at: www.themisinc.com
Also: www.themisinc.com/webinars
Objectives
Upon successful completion of this webinar, you will be able to:
– Describe the advantages of using Java on the mainframe
– Explain where can Java be used in the mainframe environment
– Discuss how Java is supported in DB2, CICS, and in batch jobs
– Describe how to access z/OS-based files from Java programs
– Discuss ways in which Java code can interact with COBOL modules
– Explain how the WebSphere server plays into mainframe modernization
– Describe the role played by message queues and XML in this effort
– Explain how Java can be used as a Web Service provider and consumer
2
Legacy System Lifecycle
• Application lifecycle
– Starts with initial development and implementation
– Followed by maintenance, modernization and replacement
– The modernization and replacement phases are
particularly relevant for Java applications on z/OS
• Eventually, ongoing maintenance is no longer acceptable
– Obsolete user interfaces
– Incompatible operating environments
3
Screen Scraping
• One simple approach: implement a wrapping layer
– Provide newer interfaces
– Technique known as screen scraping
• Advantages of screen scraping
– Tools exists to facilitate transforming existing applications
– Protects the investments in existing applications
– Less risky than replacement with a newer system
• However…
– Underlying applications are not modernized
– Makes these solutions difficult to maintain
4
Legacy System Replacement
• Replacement – last phase of legacy system lifecycle
– Legacy system is completely replaced with a new system
• Involves greater risk
– No guarantee that new system will provide better service to users
in spite of good intentions and design of the new application
• Legacy systems must not be dismissed lightly
– Have been supporting the business successfully for many years
• New systems may need to access resources based on z/OS
– Such systems may also benefit from Java batch components
– Opportunities to modernize application portfolio exist here as well
5
Considerations for Replacement
Factors to consider when replacing a legacy application:
1. Availability of skills, especially looking toward the future
–
COBOL developers are a dwindling resource
–
Many Java developers coming out of our universities
–
More tools to increase developer productivity in the Java realm
2. Integration with other systems over the network
–
Proven integration frameworks
3. Performance as measured by application throughput
–
Java has been improving in this regard (e.g.: JIT compiler)
4. Portability allows execution in other operating environments
–
Applications may be moved off of z/OS (e.g. to Unix or Linux)
–
Java: write once, run anywhere
6
Why Use Java?
• Object oriented programming (OOP)
– Many benefits
• Portability: compiled code can run on any OS
– Java compiles to bytecode, not native machine language
– A Java Virtual Machine (JVM) interprets the bytecode
• Complete language
– Supports all programming constructs
• Including support for multi-threading
• Full support for dynamic website development
– Using Java Enterprise Edition (Java EE aka J2EE)
• Widespread support and many available add ons
7
Other Benefits of Using Java
1. Functionality
– E.g. ability to send an e-mail or update a remote database
– Availability of numerous existing reusable objects
2. XML processing
– Java has mature frameworks for processing XML data
– Also full support for Web Service clients and providers
3. Reusing Java EE online program logic
– Batch jobs on z/OS often manage complex and heavy workloads
4. Migrating Java applications for QoS / server consolidation
– z/OS is the platform of choice in many situations today
5. zIIP processor can run most instructions in Java applications
– COBOL programs can only use a General Purpose processor
– Can result in significant cost savings
8
Batch Java
Batch Applications
• Features of batch applications
– No terminal or browser waiting for job output
– Typically process a large workload
• Repeat a task thousands or even millions of times
– Can result in more efficient processing
• Throughput can be increased via batch execution
– Utilize workload management techniques
10
Java Batch Application Scenarios
• Some scenarios that lend themselves to considering Java:
1. Processing large volumes of data in batch
• Flat files, VSAM data sets or DB2 data
2. Communication with other environments via messaging
• Allows an application to integrate with other environments
3. Generating and printing reports
• Large amounts of print work to be completed in batch
4. Independent Software Vendor (ISV) applications
• Software solution providers may deliver Java batch applications
to support the industry-specific needs of your organization
11
Java Batch Capabilities
What you can do in a Java on z/OS batch environment:
– Call DB2 stored procedures
• Using Java Database Connectivity (JDBC)
– Read from and write to various types of files including
MVS data sets, VSAM data sets and UNIX files
– Call programs in CICS or IMS
• Using Java Connector Architecture (JCA)
– Access the network using protocols such as TCP/IP and HTTP
– Perform CPU-intensive calculations
– Integrate with other programming languages using
• Java Native Interface (JNI)
• Language Environment (LE)
12
APIs for Java Batch Processing on z/OS
• IBM uses a common code base for the JVM on all its platforms
• Java APIs provided by a z/OS extension support:
1. MVS data set and VSAM access to interact with z/OS specific data
2. Condition code passing for integration of Java batch jobs into z/OS job nets
3. z/OS Catalog search
4. Interaction with the MVS Console
5. Conversion of COBOL/ASM data types to Java types
6. Invoking DFSORT to effectively sort data
7. Access to z/OS Access Method Services (IDCAMS)
8. RACF APIs to integrate Java into the z/OS security model
9. Writing of Log streams (e.g. as an Appender to log4j)
10.Submission of Jobs from Java
13
Data Access with Java on z/OS
• Data access is a central component of batch processing
– Data on z/OS typically resides in DB2 on z/OS
• JDBC supports access to relational data (more to come)
– Still, much z/OS data is often stored in sequential files,
partitioned data sets and VSAM clusters
• Java APIs exist to access these z/OS specific data stores
– Data access support is provided by the JZOS toolkit library
• JZOS supports Java access to mainframe file systems
– Ordinary Java APIs do not support access to these types file
14
JZOS Toolkit Library
• JZOS toolkit library is available for Java applications
– Supports access to mainframe file systems
• Not available via the standard Java I/O library
– JZOS provides thin wrappers for z/OS C/C++
Library functions to access MVS data sets
• JZOS allows Java access to any MVS data sets, including:
– Sequential files
– Partitioned Data Set (PDS) and
Partitioned Data Set Extended (PDSE)
– Virtual Sequential Access Method (VSAM)
including KSDS, RRDS, and ESDS
15
Creating Java Record Classes
• z/OS datasets often contain records described by
COBOL copybooks
– Contain fields that conform to the set of valid COBOL types
• Alpha, alpha-numeric, unscaled numeric, packed decimal, binary, etc.
– A Java program may need to process this kind of dataset
• May be difficult to convert from COBOL to Java data types
• JZOS offers a complete set of field converter types
– Operate on a byte array
– Convert from COBOL types to Java types
16
Generating Java Record Classes
• Build Java record class programatically from a copybook
– Automated process uses input from the COBOL copybook
• JZOS includes development time tools for doing this
– It is a development time tool and is not required at runtime
– Uses the ADATA output of z/OS Enterprise COBOL compiler
– Generates a Java class to map a selected copybook record
• Client-side script is used to create Java record classes
– Submits a job to generate an ADATA file for a COBOL copybook
• Machine readable file describing structure and content of compilation
– Downloads the file and runs RecordClassGenerator
• Which uses ADATA file to generate the associated Java class
– Generated Java record classes can be used like any other Java class
17
Java
Interoperability
with IMS
Java Interoperability with COBOL & PL/I
• Two ways to achieve interoperability between Java
and other languages:
1. Using functionalities of the runtime environment:
• CICS, IMS, DB2, WebSphere Application Server (WAS), or JES
• Depends heavily on the selected run time
2. Creating direct language calls
• Not bound to a runtime environment
• Java methods can be invoked from object-oriented (OO) COBOL
– Supported by using Java Native Interface (JNI) technology
• COBOL programs can also be invoked from Java code
19
Java in IMS
• IMS provides a batch processing option
– Exploits the reliability provided by IMS through specific
methods for checkpoint, restarting, and rollback
• IMS Java batch applications support access to data residing in
– IMS databases
– DB2 databases
– VSAM files
– GSAM files
• Java Message Processing (JMP) and Java Batch Processing (JBP)
applications can access IMS databases
– Uses the IMS hierarchical database interface for Java
• Requires the IMS Base API for Java to convert the Java calls to DL/I calls
20
Java Batch Processing in IMS
• Batch processing with Java in an IMS environment is supported
– Programs in JBP regions can access IMS message queues for output
– They can be started using JCL (or using TSO)
• The JBP container provides transactional services
as well as supporting checkpoint / restart processing
– Data changes are bundled into transactions to ensure data integrity
• Changes are either executed completely or not at all
• Batch processing transactions are established by IMS checkpoints
– At a checkpoint, IMS commits all data changes since the last checkpoint
– A batch process can be restarted if does not successfully complete its work
• The IMSTransaction class supports calls to
checkpoint(), restart() and rollback()
21
Java and DB2
Java in DB2 for z/OS
• DB2 for z/OS can also be used as a Java batch run time
– By using DB2 Java stored procedures
• Allows Java programs to benefit from DB2 these functionalities:
– Transactional processing
• Allows a Java program to use the transaction context of the calling program
– Including two-phase commit support
– Java Virtual Machine (JVM) instantiated only once
• JVM for a DB2 Java stored procedure is started only when it is first called
• DB2 reuses the started JVM for subsequent calls to a stored procedure
– Reuse of DB2 thread
• Stored procedures use the same DB2 thread for processing SQL statements
as the process that called the stored procedure
– Scalability
• Several stored procedures can run at the same time within one address space
• Integrated Workload Manager can start additional address spaces if required
23
Static SQL vs Dynamic SQL
• DBAs prefer static SQL; developers may prefer Dynamic SQL
– Static SQL
• Compiled and bound to the database during application development
– Dynamic SQL
• Compiled at runtime, requiring SQL to be optimized when run
• Compile at run time increases total statement execution time
• Errors in the SQL statement won’t be detected until runtime
• Benefits of Static SQL
– Compile time bind runs optimizer at development time
– Security can be managed better
• Disadvantages of Static SQL
– Need to bind before runtime
– JDBC does not provide support
• Except through its ability to call Stored Procedures
24
Static SQL vs Dynamic SQL
• Benefits of Dynamic SQL
– IDEs and APIs such as Eclipse and JDBC support it
– Better statistics – because the statement is compiled
at runtime, it uses the latest statistics available
• May result in a better execution plan
• Disadvantages of Dynamic SQL
– Compile at runtime can be a problem for several reasons:
• Every time a statement is executed, it needs to be compiled
– Increases the total statement execution time
– May slow overall performance instead of improving it
– Errors in the SQL statement will not be detected until runtime
25
Stored Procedures
• Pre-coded SQL usually contained within programming logic
• Highly recommended and widely used in many organizations
– Less vulnerable to attacks
– Can be written with static SQL
• JDBC can be used to call Stored Procedures (SPs)
– Writing the actual Stored Procedures may also be done with Java
• Each DBMS provides its own language support for writing SPs
– DB2 SPs can be written in commercial languages, such as COBOL
• SQL/PL is preferred for DB2 stored procedures today
26
JDBC
• Framework composed mainly of interfaces
–
–
–
–
Defined by Oracle
Implemented by database drivers
Same functionality regardless of driver
Switching databases requires minimal code changes
• Java Application Programming Interface (API)
– Provides access to any type of tabular data
– Normally used to access Relational Databases
– Vendor independent
• Allows Java applications to easily
– Connect to data source
– Create and execute queries and updates
– Retrieve and process query results
27
JDBC Basics
• Java Database Connectivity (JDBC) is a standard for accessing
relational databases using vendor independent java commands
– It utilizes SQL and supports calling stored procedures
• Vendors create JDBC drivers for their database products
– Insulate Java developers from the idiosyncrasies of their specific
implementation of relational database specification
• Basic Steps of JDBC Processing
1.
Load a driver or access a Connection Pool
2.
Open a Connection to the database
3.
Create a Statement (QUERY, UPDATE, INSERT, DELETE)
4.
Execute the Statement (may be a stored procedure call)
5.
Process your ResultSet (for SELECT statements)
6.
Close your Connection
28
WebSphere XD
Compute Grid
Java Batch Applications
• Today’s z/OS batch workloads often use COBOL
– Contain complex business logic
– Process large amounts of input and output data
• Java batch applications can run on z/OS
– However, a JVM is created for every batch job
• More CPU usage
• Additional resource consumption
• Greater overall cost
– Managing JCL via a workload scheduler
can help to mitigate these costs
30
WebSphere Can Help
• WebSphere Application Server for z/OS
– Provides many container services
– Allows Java execution to utilize the
On Line Batch Processing paradigm
• WebSphere Extended Deployment (XD) Compute Grid
– Provides a batch container for Java EE applications
– Extends the existing WebSphere core functions
– Uses the same administrative console as WebSphere
Application Server for z/OS
31
WebSphere XD Compute Grid
Advantages of Java EE platform:
– Supports concurrent Java batch and OLTP workloads effectively
– Optimizes performance of business-critical applications
• Maximizes scalability for high volume transaction processing
– Centralizes WebSphere and non-WebSphere server management
– Simplifies and improves management of complex system operations
• Real-time visualization tools
• Application versioning support
• Autonomic capabilities such as health management
• Reduced cost and complexity of managing WebSphere resources
– Allows greater focus on WebSphere to configure resources
• Helps increase enterprise’s adaptability to business change
– Improves customer service levels
– Takes advantage of existing Java skills and resources
32
Java Enterprise Edition (Java EE)
• WebSphere has become increasingly important
– Popular environment for modern, enterprise-class business applications
• Especially OLTP applications
• Java EE skill base is rapidly growing in the industry
– The Java language and Java EE servers offer many advantages
• Now provide a good option for batch workloads
• Today, Java can reduce application development cost over older languages
– Because it is object oriented, Java can also reduce development time
• Many powerful Java applications and frameworks are available
– Further reduces application development cost and time requirements
• Additionally, JVM performance is continually improving
• This makes Java attractive for developing new business applications
– And for re-engineering existing applications
33
The Java EE Environment on z/OS
• WebSphere Application Server (WAS) for z/OS
– Supports enterprise-class business applications written in Java
– Typical OLTP workload in WAS includes various types of clients:
• Web clients
• EJB clients
• MQ messages
• Web Service clients
WAS on z/OS
HTTP Request
HTTP Response
Traditional OLTP
JEE Application
(business logic)
Database
– WAS-based applications are often transaction-oriented
• Business logic written in Java is invoked to create a response for the client
• WAS is able to manage all of the transactional processing
34
Container Services
• WebSphere provides many system services (container services)
–
–
–
–
–
–
Security management
Transaction support
Web service support
Session and connection pooling
Caching
Messaging
• The container services provide these benefits
–
–
–
–
Simplifies Java application design
Accelerates development time
Simplifies application management
Increases application security, availability, performance, and stability
• However…
– WAS-based business logic is not accessible from traditional batch
– Integrating traditional runtime environments
and WAS is based on connectors and messaging
35
Batch Workloads for Java EE
• WebSphere XD Compute Grid supports batch workloads
– Able to run concurrently – like traditional batch on z/OS
– Expands on existing z/OS support for WebSphere
– Able to run both transactional and batch Java workloads
– Provides a batch container
• Makes existing WAS-based business
logic accessible to traditional batch
– Can be seamlessly integrated into the
traditional batch execution environment
– Can be shared across batch
and OLTP applications
36
WebSphere XD Compute Grid Overview
• WebSphere XD Compute Grid for z/OS
– Builds on existing Java EE programming model and container services
– Provides a job scheduler and an execution environment
• Includes additional features designed for long-running batch applications
– Provides an environment for deploying Java batch applications
– Modeled after the z/OS Job Entry Subsystem (JES) using
• Job Control Language (JCL)
• A job dispatcher and
• Job executors (JES initiators)
WAS on z/OS
Web clients
HTTP Request
MQ messages
HTTP Response
Traditional OLTP
JEE Application
(business logic)
JDBC
DB2
JCA
CICS
EJB clients
Web Service clients
External Scheduler
Batch Request
37
Compute Grid Components
• WebSphere XD Compute Grid components are Java EE applications:
– xJCL – XML based job control language
– Job Scheduler (JS) – a job dispatcher – job entry point to Compute Grid
– Grid Execution Endpoints (GEE) – multi-threaded job executors
– Parallel Job Manager (PJM) – governs execution of parallel batch jobs
• Components can be placed in one JVM or in a clustered environment
– Support WAS security, scalability, availability, and life cycle management
• Other components used in a Compute Grid environment include:
– Job Management Console (JMC)
– Scheduler tables – job information stored in a database
– Container tables – checkpoint information stored in a database
38
Compute Grid Component Detail
• Components used in a WebSphere XD Compute Grid environment:
– Job scheduler (JS) – job entry point to XD Compute Grid
• Provides job life-cycle management functions (submit, cancel, restart) and monitoring
• Maintains a history of all jobs (waiting, running, or completed) and job usage data
• Dispatches workload to either the PJM or GEE and also hosts the JMC
– Batch container – Grid Execution Endpoint (GEE) component
• Executes the actual business logic of the batch jobs
• A WebSphere cell can have any number of batch containers
– Java EE batch application – WebSphere applications deployed as an EAR file
• Contains implementations of one or more Java batch applications
– JDBC – provides connectivity to the scheduler and container tables
– Parallel Job Manager (PJM)
• Breaks large batch jobs into partitions for parallel execution
• Not a required component in a WebSphere XD Compute Grid environment
39
JZOS Launcher
• JZOS delivers both the JZOS Launcher and Java z/OS APIs
– The Launcher allows a stand-alone Java program to be invoked using JCL
– It also plays a role in a WebSphere XD Compute Grid environment
• Its APIs provide an integration point for Java and traditional z/OS
• The JZOS launcher has several drawbacks making it inefficient
for the high volume of batch jobs that run within batch window
– It lacks these capabilities:
• Security, transaction, or connection management facilities
• Checkpoint / restart facility for batch jobs
• High availability and other quality of service (QoS) provided by WAS
• A persistent, reusable JVM – each job step requiring Java reloads the JVM
40
Compute Grid vs. JZOS
• WebSphere XD Compute Grid offers all necessary
Quality of Service and other services including:
–
–
–
–
–
–
Persistent, reusable JVM and execution container
Security, transaction, and connection management
Thread pooling
High availability
Prioritization
Integration with z/OS WLM
Java Standard Edition
Java application
(business logic)
ZFS
JES
External
Scheduler
HFS
JCL
WebSphere XD
Compute Grid for z/OS
VSAM
Java application
(business logic)
41
Programming with Compute Grid
• WebSphere XD Compute Grid batch container
– Contains and controls the Java batch application
– Uses a container-managed thread defining the unit of execution
– Carries out the job's life cycle as it runs in the batch container
• A batch application is made up of these components:
– Batch job step
• Java class providing the business logic to execute as a step in the job
• Invoked by the batch container during job processing
– Batch data stream
• Provides the job step with access to various types of data including
–
–
–
–
Relational databases
File systems
Message queues
J2C connectors to other types of data
42
Batch Container Responsibilities
• During life cycle of a job step, batch container is responsible for
open, close, and checkpoint-related callbacks on batch data streams
– Job step calls methods on batch data stream to get and put data
• Batch applications may include either or both of these components:
– Checkpoint algorithm
• Container provides mechanism to support job restart
• Compute Grid provides two pre-built checkpoint algorithms
– One supporting a time-based checkpoint interval
– One supporting a checkpoint interval based on record-count
– Results algorithm
• A return code is supplied upon completion of each job step
• The overall return code for the job as a whole is returned
– A provided results algorithm returns the highest
step return code as the overall job return code
43
JCICS – Using
Java with CICS
Using Java with CICS
• Java has been available as a programming language in CICS
since CICS Transaction Server (TS) V1.3
– Support has steadily improved over a number of releases
– CICS TS V4.2 is of particular significance for modern workloads
• CICS TS V4.2 fully utilizes the JVM server model
– Embraces modern dynamic application development technologies
through the Open Services Gateway initiative (OSGi) technology
– Introduces a rich client development platform via the CICS Explorer
– Provides capacity and workload benefits via 64-bit storage for JVM
• Delivers significant gains in performance and scalability
over previous versions of CICS Java support
– Further benefits are realized by embracing the CICS bundle resource
for packaging, deployment, and controlling the application lifecycle
• Further improves manageability and deployment of CICS Java applications
45
JVM Server Replaces Pooled JVMs
• More powerful JVM server model introduced in CICS TS V4.1
– Previous "pooled JVM" model is no longer strategic to CICS
• Still available and supported in CICS TS V4.2
• Removed entirely in CICS TS V5.1
• JVM server is strategic direction for Java CICS applications
– More standard Java behavior of the JVM
– Supports a multi-threaded architecture
– Migration of applications from pooled JVM to JVM server recommended
• Primarily a “repackage and redeploy” operation
– With pooled JVM, a “new” JVM is started for each task
• JVM Server, with a single JVM, requires Java code to be thread safe
46
Open Services Gateway initiative
• Open Services Gateway initiative (OSGi)
– A module system and service platform for Java applications
• Provided by the OSGi Alliance (http://www.osgi.org)
– Addresses excessive costs of class loading and class management
• Prior to CICS TS V4.2, code changes required the JVM to be restarted
to enable reloading new classes, resulting in application downtime
– OSGi allows applications to be developed into components
• Dependencies can be made explicit and resolved ahead of time
• Applications can be dynamically refreshed or versioned
and run side-by-side in the same JVM
• OSGi implements a complete and dynamic component model
– Applications or components (in the form of bundles for deployment)
can be remotely installed, started, stopped, updated, and uninstalled
without requiring a JVM restart
47
CICS Explorer SDK
• CICS Explorer is an Eclipse-based system management tool
– Initially released as a SupportPac in 2008
– Eclipse-based graphical user interface (GUI) application
– Runs on the Windows or Linux operating systems
– Connects to either a CICSPlex or to a single CICS region
– No-charge downloadable application
– Can be extended with plug-ins for
• CICS Performance Analyzer
• CICS Interdependency Analyzer
• CICS Configuration Manager
• CICS Transaction Gateway
– Supports development of Java applications to run in CICS
– Supports creation and deployment of CICS Java OSGi applications
48
Support for Axis2 Technology
CICS can act as either a web services provider or requester
– CICS implements the pipeline concept
• Service requests, inbound or outbound, go through a series of handlers
to process the web service being called or to call another web service
• The pipeline is the bridge between the web service request, typically in
XML, and the CICS resources needed to process or make the request
• These pipelines in CICS call a series of handler programs to process
the incoming or outgoing SOAP messages
• In previous versions of CICS, none of these handlers were written in Java
– CICS TS V4.2 supports use of the Axis2* Java based SOAP engine
to process web service requests in provider and requester pipelines
• Axis2 is an open source web services engine from the Apache foundation
provided with CICS to process SOAP messages in a Java environment
• Since Axis2 uses Java, the SOAP processing is eligible for offloading to
System z Integrated Information Processor (zIIP) it runs in a JVM server
49
Interfacing With Language Structures
• CICS is a well established mature environment
– Millions of lines of application code written using COBOL or PL/I
– Java code may need to interact with these applications
• Java programs must be able use structured data from those applications
– E.g., link to a COBOL program passing a commarea (or a channel) where
the data inside the channel or commarea is defined in a COBOL copybook
• Typically used where VSAM file records or database records are accessed
– Copybooks must be converted into Java constructs that Java programs
can easily manipulate
• CICS supports tools which can be used to import copybooks
• Allows use of structured data from other programming languages in Java code
50
Java Development Using JCICS
CICS Java class library (JCICS)
– Used by Java applications to access CICS services
– Is the Java equivalent of the EXEC CICS application
programming interface
• API provided for other CICS supported languages, such as COBOL
– Can integrate with programs written in other languages
– Supports most of the functions of the EXEC CICS API
– Is included with CICS and with the CICS Explorer® SDK
51
Arguments for Passing Data
• Pass data between programs using a communication area
(COMMAREA) or by using channels and containers
– COMMAREA supports passing a maximum of 32 KB at a time
– A channel and containers supports passing more than 32 KB
• The COMMAREA or channel, and any other parameters,
are passed as arguments to the appropriate methods
– For example, the Program class includes various link() methods
• One version passes a CommArea, optionally including a length
• Another version passes a Channel with one or more Containers
52
Java and Messaging
Message-Oriented Middleware
• Message-Oriented Middleware (MOM)
–
–
–
–
Software or hardware infrastructure
Supports sending and receiving messages between distributed systems
Allows distributing application modules over heterogeneous platforms
Simplifies development of applications that span multiple operating
systems and network protocols
– Creates a distributed communications layer
• Insulates developers from operating systems and network interface details
– Support asynchronous calls between the client and server applications
• Enterprise Messaging System (EMS)
– A set of published enterprise-wide standards
• Allows organizations to send messages between computer systems
– Promote loosely coupled architectures
• Allow message formats to change with minimum impact on message clients
54
Java Messaging Service (JMS)
• JMS is a standard API that is part of the J2EE platform
– Used to access enterprise messaging systems
– Enables loosely coupled (asynchronous) communication
• A JMS provider delivers messages to a client as they arrive
• Clients need not request messages in order to receive them
• Similar to JDBC in that it allows access to many different
enterprise messaging systems, such as IBM MQ
– Previously called WebSphere MQ … and MQ Series before that
• Applications that use JMS for sending or receiving messages
are portable across JMS vendors
• Java EE Servers are required to have support for JMS
55
JMS Terminology
JMS clients
Java applications that use JMS
JMS providers
Messaging systems; route and deliver messages
JMS application
Business system using JMS clients & providers
Messages
Communicate information between JMS clients
Producer
JMS client that sends a message
Consumer
JMS client that receives a message
Administered objects
Preconfigured JMS objects
- Created by an administrator for the use of clients
- Two types: destinations and connection factories
56
Java , XML and
Web Services
What is XML?
• eXtensible Markup Language
– Simple, flexible text format
– Derived from SGML
• Standard Generalized Markup Language
– An ISO standard ( ISO 8879)
• The XML specification is based on recommendations
by the World Wide Web Consortium (W3C)
• Fully supported in IDEs such as Eclipse and RAD
• Full Java support for processing XML data
58
Use of XML Documents
• XML is playing an increasingly important role
in the exchange of a wide variety of data on the Web
– E.g. business-to-business e-commerce
• Can be used to store data in files or databases
• Can be used as a means for exchanging platform
independent data for distributed computing
• Used to describe application configuration
59
A Well-Formed XML Document
<?xml version="1.0" encoding="UTF-8" ?>
<class title="DB2 for z/OS Advanced SQL">
<date>July 25 – 29, 2016</date>
<instructor>David Simpson</instructor>
<location>ABC Training Center</location>
<city>Westfield</city>
<state>NJ</state>
<student>
<name>Susan Lee</name>
<company>Sun Star Bank</company>
</student>
<student>
<name>Edward Rice</name>
<company>West Telco</company>
</student>
</class>
60
Web Service
• Definition
– Interface that describes a collection of operations that are
network accessible through standardized XML messaging
– Accessed via common Internet protocols and data formats
•
•
•
•
HTTP
TCP/IP
XML
SOAP
Hides implementation details so that it can be
used independently of the hardware or software
platform on which it is implemented and regardless
of the programming language in which it is written
• Benefits
–
–
–
–
Separate systems can communicate and share services over the Internet
Technology is not tied to a specific platform or implementation language
Facilitates the reuse of legacy systems in new applications
Loosely coupled services
• Interact only through stable interfaces (contracts)
– Based upon industry standard protocols
• Results in universal support
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Roles of Web Services
• Integration of application functionality within an organization
over an intranet, internet or extended virtual private network
Web Service
Intranet or VPN
Linux
Windows
Legacy Systems
Unix
62
Roles of Web Services
• Business to Business (B2B)
– Integration of applications between business partners via the internet
Business 2
Web
Service
Web
Service
Internet
Business 1
Web
Service
Business 3
Web
Service
Business 4
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Roles of Web Services
• Business to Customer (B2C)
– Integration of business services with client applications
Web Service
Internet
Client Application
Client Application
Client Application
Client Application
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Web Services
Communication Architecture
Three main components
– Consumer
– Communication
– Web service
Consumer
Web Service
Requestor
Listener
Caller
XML
XML
Listener
Communication
Parser
Responder
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Java Web Services (JWS)
• Hosted in J2EE Web Container
– Each Java application in a container has a Context Root
• Uniquely defines the location of its services
• Exposes methods of a Java class using annotations
• Rational Application Developer (RAD) provides tools
• Java bindings allow mapping an XML message to a java class
• Can create a Java Web service from the bottom up
– Turn existing Java component into a Web service
• Or from the top down
– Generate a Java bean skeleton for a Web service from a WSDL
• Web Service Descriptor Language defines details of a web service
66
Web Service Client
• Any application that uses (invokes) a Web service
– Client could even be a Web service itself
• Needs to know how to access the Web service
– Defined by the WSDL for that Web service
• RAD can use a WSDL file as input to
– Automatically generate a Java proxy class to simplify
communication with the Web service defined by the WSDL
– Handles remote communication with the Web service
• The Web service client needs to obtain the WSDL
– May be found using a UDDI directory, via a URL, or privately
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A RESTful Alternative
• REST: Representational State Transfer
– A way to define and access resources on a network
• Resources are identified by a URI
– REST is data-centric, where SOAP is API-centric
– Very simple interface
• Simple URIs with HTTP methods such as GET and POST
• Much simpler than SOAP-based messaging
• Sample REST service performing a catalog lookup
– To lookup an item by its ID, simply issue a GET request to this URI
http://www.themis.com/catalog/rest/items/12345
– The REST service will returns the item with that ID
– Various options of format of return data (text, JSON, XML)
– No WSDL, no SOAP – quite simple
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REST vs. SOAP
• REST is simpler than SOAP
– Uses common web concepts and existing HTTP infrastructure
– Shorter learning curve – design similar to browser-based web requests
• REST is HTTP based
– SOAP is capable of using other transports
• e.g. SOAP over JMS (rare)
• REST is point-to-point
– SOAP supports intermediary nodes (handlers)
• REST has no standards for security
– Leverages existing HTTP standards
– SOAP has many additional capabilities (WS-*)
• E.g. WS-Security and WS-ReliableMessaging
• REST is newer than SOAP
– Both are mainstream SOA approaches popular today
WS-* is a shorthand for referring to the myriad additional SOAP-based Web service standards
69
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