Sams Teach Yourself BEA WebLogic Server 7.0 in 21 Days

WebLogic's Support for Enterprise JavaBeans

The EJB specification has matured from 1.1 to 2.0 with lots of attractive new features. WebLogic Server is one of the first application servers to provide support for both the EJB 1.1 and EJB 2.0 specifications. This means that developers can develop applications for both EJB specification versions. In addition, EJB 1.1 compliant applications can be easily migrated and deployed to the EJB 2.0 specification using WebLogic Server. WebLogic Server provides tools to enable developers to migrate applications compliant with the EJB 1.1 specification to the EJB 2.0 specification. The WebLogic Server supports the complete EJB 2.0 specification, from WebLogic Server version 6.1 onward.

In Figure 10.1 you can see the EJB container within the WebLogic Server. The WebLogic Server fulfills the roles of EJBServerProvider and EJBContainerProvider specified in the EJB 2.0 specification. The WebLogic Server provides an EJB container compliant with the EJB 2.0 specification with required services such as component management, connection and instance pooling, security services, and transaction services. Because the current specification assumes that the roles of EJBServerProvider and EJBContainerProvider are analogous, the WebLogic Server fulfills both of these EJB specification roles.

The current version (7.0) of WebLogic Server continues this support for the EJB 2.0 specification by introducing support for the following new features:

• Support for message-driven beans (part of the new EJB 2.0 specification) The major new addition in the EJB 2.0 specification is the inclusion of a new bean type: the message-driven bean. With message beans, the EJB specification provides support for writing stateless beans that can act as Java Message Service (JMS) API clients and process messages from a message queue. This integration of the JMS API, a part of the J2EE enterprise API suite, enables developers to write asynchronous processing applications.

• Local interfaces for session and entity beans to improve performance From the experience of developers with the EJB 1.1 specification, a major drawback that was noted was the poor performance of accessing EJBs within the same JVM. The EJB 2.0 specification provides a concept called local interfaces for session and entity beans. Local interfaces can be used to write EJBs that can be accessed in the same JVM. This avoids the overhead associated with accessing a bean in the same JVM that uses the remote interface. Both session and entity beans can implement a local interface.

• New design for container-managed persistence (CMP) The biggest drawback in the EJB 1.1 specification was the design of CMP. The limitations found in the CMP design of the EJB 1.1 specification have been overcome to a certain extent in the new CMP design of the EJB 2.0 specification. The major change implemented is support for container-managed relationships among entity beans.

• EJB-QL language to query EJBs in CMP To support the new CMP model of container managed relationships, the EJB 2.0 specification defines a meta-language called EJB-Query Language (EJB-QL).

These new features of the EJB 2.0 specification supported by WebLogic Server 7.0 will be covered in coming days.