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The art of EJB deployment

Write universal EJBs without all the hassle

By James Caple and <a Href="javascript:openbrwindow()">mike Haim Altarace</a>, JavaWorld.com, 08/03/01

The slogan "Write once, run anywhere" is Sun's way of characterizing Java's platform portability. However, to most Java developers, the slogan more closely represents a noble, and somewhat lofty, objective, rather than real-world Java application deployment. For example, getting your Java applet code to run the same in both Netscape and Internet Explorer can be a trying exercise. Similarly, coaxing Java applications to run the same way on different Java-compatible platforms sometimes requires diligence, patience, and thorough testing.

Don't get us wrong, though. Java is a great technology, especially when used for server-side solutions. And in our opinion, there is no better environment than the Java 2 Platform, Enterprise Edition (J2EE) to develop Web services. However, when working with Enterprise JavaBeans (EJBs), deploying the same EJB code on different platforms can present similar sets of challenges. Although writing universally deployable EJB code is entirely possible, the code and application server must comply with the same EJB specification version. However, an EJB deployer must often go through a different process to properly install and deploy an EJB from one application server to the next.

From a beginner's perspective, this article addresses some EJB packaging nuances associated with deploying the same EJB code from several different application servers, namely BEA's WebLogic, IBM's WebSphere, and the open source community's JBoss application servers.

The EJB deployment process

The EJB deployment process tends to vary between application servers for several reasons. First, the EJB specification provides minimal guidance in describing how you deploy EJBs. Therefore, vendors adhere to the J2EE/EJB specification to varying degrees; they use their own discretion in defining the deployment process for their specific platforms.

Second, since deployment is an area where application server vendors can add value and uniqueness to their product, they are not motivated to standardize the process. In addition, this lack of standardization presents opportunities for application server and Java IDE vendors to integrate their toolset offerings to facilitate EJB development and deployment -- a process only facilitated if your preferred IDE supports your targeted application server. Nevertheless, the process for deploying a given EJB must be taken on a case-by-case basis, and is usually unique to each application server.

To illustrate this, we experimented with two EJB implementations, a Lightweight Directory Access Protocol (LDAP) stateless session bean and a simple container-managed persistence (CMP) entity bean. In this article, we identify some of the major differences associated with deploying the same EJB code in WebLogic, WebSphere, and JBoss application servers. One notable caveat: we did as much as possible by hand (we wrote our code and deployment descriptors, and created the jar files using vi/Emacs and the JDK's jar utility), all the while recognizing that EJB deployment may go smoother if we use enterprise development tools closely aligned with a specific application server vendor (e.g. VisualAge for Java used in conjunction with WebSphere).

 

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