Summary

Today, you looked in more detail at J2EE and the facilities that it provides. You saw how the different J2EE technologies fit into the n-tier model, and how it provides component frameworks for different types of functionality. You have also seen how Enterprise JavaBeans (EJBs), JavaServer Pages (JSPs) and servlets are the main user-defined components of a J2EE application. You have also seen how supporting J2EE technologies are used to provide cross-component functionality, such as data access, network communication, naming services, transaction management, and security.

You have seen that the separate functions of tool provider, developer, assembler, deployer and administrator work co-operatively to implement and manage the many stages of the lifecycle of a J2EE application. The components of an Enterprise Application are packaged into a single EAR file and this file contains components packaged as JAR files, Web archives (WAR files), or resource archives (RAR files). Each constituent archive file (EAR, WAR, RAR or JAR) includes the required Java class files, and a component-specific deployment descriptor (DD). A deployment descriptor describes not only the component itself, but also the environmental requirements for the container that will host the component.