XDoclet is an open-source code-generation engine. Building the enterprise applications in Java involves working with Enterprise Java Beans (EJB) and that means writing a lot of deployment decriptors for your application configuration, a time-consuming job. XDoclet helps you avoid this overhead by generating these descriptors and other source code files for you. XDoclet was initially aimed at simplifying EJB development but its scope is no longer limited to EJB. You specify certain tags similar to Javadoc tags in your source code and XDoclet reads those tags to decide how to generate the required source files.

A typical XDoclet tag consists of the following values:

@namespace.tag-name attribute-name="attribute value"

Each tag belongs to a namespace and the tag name is unique within that namespace. Each tag can have one or more attributes and the corresponding value for that tag.

Let us have a look at the XDoclet tags inside an Entity Bean.

/**
 * @ejb.bean
 *     name="Address"
 *     jndi-name="ejb/addr/Address"
 *     view-type="local"
 *     primkey-field="id"
 *     type="CMP" 
 *
 * @ejb.finder
 *     signature="Collection findByStreet(java.lang.String street)"
 *     unchecked="true"
 *
 * @ejb.finder
 *     signature="Collection findByCity(java.lang.String city)"
 *
 * @ejb.finder
 *     signature="Collection findByOwner(test.interfaces.Customer owner)"
 *
 * @ejb.value-object
 *     name="Address"
 *     match="*"
 *
 * @ejb.persistence
 *     table-name="address"
 *
 */

The code here uses the tag "bean" from the "ejb" namespace to define the properties that apply to EJB. For example:
name specifies the name of the Entity Bean.
jndi-name specifies the jndi-name used to access the database.
view-type specifies if the enterprise bean is local or remote or both.
primkey-field specifies the primary key field.
type specifies the bean type, such as BMP or CMP, for example.

Similarly there are other tags such as finder, transaction and interface to indicate the XDoclet for generating the required information in the source files.
 
XDoclet provides different namespaces for generating the application-specific deployment descriptors. For example, the "jboss" namespace includes tags for the Jboss Open-Source application server. XDoclet provides support for many application servers such as Bea, Websphere, Oracle, Orion and more.

XDoclet is generally used with Apache Ant tool, a popular build tool used for Java development. You can add your XDoclet tasks inside the build.xml file so that it generates the required files for you by executing that target from the Ant tool. By integrating XDoclet with Ant and other tools such as JUnit, you can achieve continuous integration throughout your project.

For example, the target for generating EJB-specific source files could be added into an Ant build file in the following manner. This example generates an deployment descriptor for a Sun One-Application Server.

Download the above code (pdf)

This task uses the xdoclet.modules.ejb.EjbDocletTask class from XDoclet to generate the EJB-specific files such as local interface, local home interface, EJB deployment descriptor and deployment descriptor for a Sun One-Application server.

To compile, package and deploy the generated EJB files, you can add more tasks to the build.xml file as mentioned below.