Structure of a Java EE Application

 

A Java EE module consists of one or more Java EE components for the same container type and, optionally, one component deployment descriptor of that type. 

Java EE modules are of the following types:

• EJB modules, which contain class files for enterprise beans and an EJB deployment descriptor. EJB modules are packaged as JAR files with a .jar extension.
• Web modules, which contain servlet class files, web files, supporting class files, GIF and HTML files, and a web application deployment descriptor. Web modules are packaged as JAR files with a .war (web archive) extension.
• Application client modules, which contain class files and an application client deployment descriptor. Application client modules are packaged as JAR files with a .jar extension. 
• Resource adapter modules, which contain all Java interfaces, classes, native libraries, and other documentation, along with the resource adapter deployment descriptor. Together, these implement the Connector architecture for a particular EIS. Resource adapter modules are packaged as JAR files with an .rar (resource adapter archive) extension.

An Enterprise Archive (EAR) file contains Java EE modules and, optionally, deployment descriptors. 

Deployment Descriptor

A deployment descriptor, an XML document with an .xml extension, describes the deployment settings of an application, a module, or a component. Because deployment descriptor information is declarative, it can be changed without the need to modify the source code. 


At runtime, the Java EE server reads the deployment descriptor and acts upon the application, module, or component accordingly, i.e. with specific container options, security settings and describes specific configuration requirements.

In Java EE, there are two types of deployment descriptor: 

•  Java EE deployment descriptors, and 
•  Runtime deployment descriptors 

 A Java EE deployment descriptor is defined by a Java EE specification and can be used to configure deployment settings on any Java EE compliant implementation. For example, the web.xml file is a standard Java EE deployment descriptor, specified in the java servlet specification. 

A runtime deployment descriptor is defined by the vendor of each container implementation.It is used to configure Java EE implementation-specific parameters. For example, the GlassFish Server runtime deployment descriptor contains such information as the context root of a web application, as well as GlassFish Server implementation-specific parameters, such as caching directives. The GlassFish Server runtime deployment descriptors are named sun-moduleType.xml and are located in the same META-INF directory as the Java EE deployment descriptor.