Packaging EJB 3 Applications(ejb-jar.xml persistence.xml applicational.xml)

地址:http://www.developer.com/java/ejb/article.php/3670496/Packaging-EJB-3-Applications.htm


he real success of Java EE applications lies in assembly and deployment, as this is the key to delivering on Java's promise of write once, run anywhere (WORA). If you fail to fully grasp this step, your application may not realize this level of portability.

Java platform roles: it's all about juggling hats
The Java EE platform defines different roles and responsibilities relating to development, assembly, and deployment of Java EE applications. In this article we are mainly interested in the Developer, Assembler, and Deployer roles, but we introduce you to all the roles so that you can be familiar with them. The roles defined by the specifications are

Enterprise Bean Provider
Application Assembler
Deployer
EJB Server Provider
EJB Container Provider
Persistence Provider
System Administrator
The database administrator is not one of the defined Java EE roles. The database administrator may not even understand a line of Java code. However, the importance of this role cannot be overlooked, especially in large corporations where relational databases are outside the control of the application developers. Developers, Assemblers, and Deployers may need to work with the DBAs in order to successfully build and release Java EE applications.

It's all about the division of labor. Many believe that the difficulties of earlier EJB practices were a result of the division of the EJB roles. In reality, the previous EJB specifications were not the real culprit—the source of all the confusion is the Java EE specification. While the Java EE and EJB specifications define seven roles, the problem is that many project teams do not even have seven people—how can a two- or three-person team wear that many hats?、



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