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EJB fundamentals and session beans

Begin exploring the world of EJBs

By Jim Crume, Kevin Mukhar, James L. Weaver and Chris Zelenak, JavaWorld.com, 02/13/06

Page 2 of 7

• Client communication: The client, which is often a user interface, must be able to call the methods of objects on the application server via agreed-upon protocols.
• Session state management: You'll recall our discussions on this topic in the context of JSP (JavaServer Pages) and servlet development back in Chapter 6.
• Transaction management: Some operations, for example, when updating data, must occur as a unit of work. If one update fails, they all should fail.
• Database connection management: An application server must connect to a database, often using pools of database connections for optimizing resources.
• User authentication and role-based authorization: Users of an application must often log in for security purposes. The functionality of an application to which a user is allowed access is often based on the role associated with a user ID.
• Asynchronous messaging: Applications often need to communicate with other systems in an asynchronous manner; that is, without waiting for the other system to respond. This requires an underlying messaging system that provides guaranteed delivery of these asynchronous messages.
• Application server administration: Application servers must be administered. For example, they need to be monitored and tuned.

The EJB specification

The EJB specification defines a common architecture, which has prompted several vendors to build application servers that comply with this specification. Now developers can get off-the-shelf application servers that comply with a common standard, benefiting from the competition (in areas such as price, features, and performance) among those vendors.

Some of the more common commercial EJB application servers are WebLogic (BEA), Java Enterprise System (Sun), OC4J containers for Oracle Database 10g, and WebSphere (IBM). There are also some very good open source entries in this market such as JBoss and JOnAS. Sun also provides an open source reference implementation (Java EE SDK) of the Java EE 5 and EJB 3.0 specifications that developers can use to develop and test applications for compliance with those specifications. (The reference implementation may not, however, be used to deploy production systems.) Currently under development, the reference implementation is codenamed "Glassfish." The platform provides a basic EJB 3.0 test platform; more details can be found on the Website and in the related discussion forums. These application servers, in conjunction with the capabilities defined in the EJB specification, support all of the features listed here and many more.

The EJB specification was created by experienced members of the development community; such a body is called an expert group. In the EJB specification's expert group are members from such organizations as JBoss, Oracle, and Google. Thanks to them, we now have a standard, specifications-based way to develop and deploy enterprise-class systems. We are approaching the Java dream of developing an application that can run on any vendor platform as-is. This is in contrast to the vendor-specific way we used to develop, where each server had its own way of doing things, and where the developer was locked into the chosen platform once the first line of code was written!

 

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