JSP Tag Libraries

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The server-side containers in J2EE not only run components like EJBs and JSPs, but provide them with lifecycle management and accessibility to other enterprise Java facilities such as JNDI, JDBC, JMS, JavaMail, as well as to other EJB and servlet/JSP components deployed in the same J2EE server. These containers create the playground in which all J2EE components and services operate, and are typically wrapped into a single product most commonly known as a J2EE application server. IBM WebSphere, BEA WebLogic, and Borland Application Server are just a few examples of J2EE application servers on the market.


1 RMI is a remote method invocation infrastructure that allows a Java program to seamlessly call methods on objects located in remote Java virtual machines (JVMs). IIOP is the communication protocol that was selected for the J2EE RMI method calls.


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Figure 12.1 Clients and servers in J2EE



Web container (servlets and JSP files)


JMS


JNDI


RMI/


IIOP


_L_


JDBC


JTA


EJB container (EJBs)


JavaMail


12.1.2    Deployment in J2EE


In addition to writing J2EE components, parts of the J2EE specification are standards for deploying and configuring applications. In J2EE, each application (or in the case of EJB, even a component) has a unique deployment descriptor containing metadata that instructs the container in deploying it, and includes a standard jar file structure (similar to the deployment descriptor and WAR format discussed in chapter 2). The deployment descriptors are XML documents with syntax as defined in the J2EE specification. These standards-based deployment descriptors and the jar file structure are essential when it comes to deploying an application, since the deployment tools can take the standard jar file and automatically import it into the application server’s configuration repository. This standard, easy deployment is one of the strengths of the J2EE architecture, ensuring that any J2EE-compliant component is deployable on any J2EE-compliant product (no matter which vendor actually makes the product). As a J2EE developer you can take the EJBs and JSPs written for your WebLogic server and run them on a WebSphere server with no fear of incompatibility.

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