Enterprise JavaBeans, Fourth Edition

Filling in the Gaps

The J2EE specification attempts to fill the gaps between the web components and Enterprise JavaBeans by defining how these technologies come together to form a complete platform. One of the ways in which J2EE adds value is by creating a consistent programming model across web components and enterprise beans through the use of the JNDI ENC and XML deployment descriptors. A servlet in J2EE can access JDBC DataSource objects, environment entries, and references to enterprise beans through a JNDI ENC in exactly the same way that enterprise beans use the JNDI ENC. To support the JNDI ENC, web components have their own XML deployment descriptor that declares elements for the JNDI ENC (<ejb-ref>, <resource-ref>, <env-entry>) as well as security roles and other elements specific to web components. In J2EE, web components are packaged along with their XML deployment descriptors and deployed in JAR files with the extension .war, which stands for web archive. A .war file can contain several servlets and JSP documents that share an XML deployment descriptor. The use of the JNDI ENC, deployment descriptors, and JAR files in web components makes them consistent with the EJB programming model and unifies the entire J2EE platform.

Use of the JNDI ENC makes it much simpler for web components to access Enterprise JavaBeans. The web component developer does not need to be concerned with the network location of enterprise beans; the server will map the <ejb-ref> elements listed ...