7.4 J2EE Connector Architecture

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The J2EE Connector Architecture is aimed at providing a standard way to access enterprise applications from a J2EE-based Java application. It defines a set of Java interfaces through which application developers can access heterogeneous EIS systems, for example, legacy systems such as CICS, and Enterprise Resource Planning (ERP) applications.

J2EE Connector Architecture 1.0 support is a requirement of the J2EE 1.3 specification. It provides access to a range of systems through a common client interface API (CCI). Application programmers code to the single API rather than having unique interfaces for each proprietary system. The link from the API to the enterprise system is called a resource adapter and is provided by a third-party vendor. This is somewhat analogous to the model for JDBC drivers. Resource adapters are packaged as resource adapter archive (RAR) files.

IBM WebSphere Application Server V5.0 supports the J2EE Connector Architecture 1.0, as required by the J2EE 1.3 specification. The administrative console supports J2EE Connector resource adapter configuration. The administrative console allows the association of connection factories for the resource adapter that encapsulate the pooling attributes. Component providers request a connection for an enterprise information system (EIS) from the connection factory through the JNDI lookup mechanism. IBM supplies resource adapters for enterprise systems such as CICS, HOD, IMS, SAP, and Crossworlds as separate products.

IBM WebSphere Studio Application Developer V5.0 supports application development using J2EE Connectors, and development of custom J2EE Connectors.

7.4.1 CICS resource adapter

The CICS Transaction Gateway (CICS TG) V5 is a set of client and server software components that allow a Java application to invoke services in a CICS region.

The CICS TG offers three basic interfaces for Java clients:

External Call Interface (ECI) for COMMAREA-based CICS applications
External Presentation Interface (EPI) for 3270-based transactions
External Security Interface (ESI) for password management to verify and change user IDs and passwords

The CICS resource adapter is covered in detail in the following chapters.

7.4.2 IMS resource adapter

The IMS Connector for Java provides a way to create Java applications that can access IMS transactions. The IMS Connector for Java uses IMS Connect to access IMS. IMS Connect is a facility that runs on the host IMS machine and supports TCP/IP and Local Option communication to IMS. A Java application or servlet accesses IMS Open Transaction Manager Access (OTMA) through IMS Connect. IMS Connect accepts messages from its TCP/IP clients and routes them to IMS OTMA using the Cross-System Coupling Facility (XCF).

The runtime component of IMS Connector for Java is provided as a component of IMS Connect, Version 1 Release 2 (Program Number 5655-E51). The J2EE Connector implementation of this runtime component is also referred to as the IBM WebSphere Adapter for IMS. It is packaged as a RAR file, imsico.rar, for deployment into a WebSphere Application Server. The RAR file is installed to a target directory from the IBM IMS Connect, Version 1 Release 2.

7.4.3 Advantages of J2EE Connectors

Some reasons to use J2EE Connectors are:

The common client interface simplifies application integration with diverse EISs. This common interface makes it easy to plug third-party or home-grown resource adapters into your applications.
Each EIS requires just one implementation of the resource adapter since there is no need to custom develop an adapter for every application.
J2EE Connectors facilitate scalability and provide Quality of Service features transparently to the client application.
J2EE Connector Architecture-compliant resource adapters are portable across J2EE application servers. If a vendor provides a resource adapter for WebLogic, for example, it should also work with the WebSphere Application Server.
J2EE Connectors have low intrusion on the enterprise system because native client interfaces are utilized.

7.4.4 Disadvantages of J2EE Connectors

Some J2EE Connector issues to consider are:

J2EE Connector Architecture has support only for synchronous communication. (The CICS adapter does offer support for non-blocking calls.) Support for asynchronous communications is expected in the J2EE Connector Architecture 1.5 specification.
The J2EE Connectors standard is still relatively new, and performance compared with previous alternatives has not been firmly established. For example, some customers may prefer to continue with the well-proven non-J2EE Connector CICS TG base classes.
Though J2EE Connector Architecture promises an abstraction to access any legacy system, with J2EE Connector Architecture 1.0, parts of the client application need to have resource adapter-specific implementation. This means that if you have to change the resource adapter (move to a different enterprise system, which provides a different adapter), the client application will be affected.

For more information on J2EE Connectors and CICS, refer to the following redbooks:

Java Connectors for CICS: Featuring the J2EE Connector Architecture, SG24-6401
Revealed! Architecting Web Access to CICS, SG24-5466

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