Enterprise JavaBeans, Second Edition

The ejb-jar File

The JAR file format is a platform-independent format for compressing, packaging, and delivering several files together. Based on ZIP file format and the ZLIB compression standards, the JAR ( Java archive) packages and tool were originally developed to make downloads of Java applets more efficient. As a packaging mechanism, however, the JAR file format is a very convenient way to “shrink-wrap” components and other software for delivery to third parties. The original JavaBeans component architecture depends on JAR files for packaging, as does Enterprise JavaBeans. The goal in using the JAR file format in EJB is to package all the classes and interfaces associated with one or more beans, including the deployment descriptor, into one file.

The JAR file is created using a vendor-specific tool, or using the jar utility that is part of the Java 2, Standard Edition development kit. An ejb-jar file contains:

• The XML deployment descriptor

• The bean classes

• The remote and home interfaces

• The primary key class

• Dependent classes and interfaces

The XML deployment descriptor must be located in the path META-INF/ejb-jar.xml, and must contain all the deployment information for all the beans in the ejb-jar file. For each bean declared in the XML deployment descriptor, the ejb-jar file must contain its bean class, remote and home interfaces, and dependent classes and interfaces. Dependent classes and interfaces are usually things like application-specific exceptions, business interfaces, ...