Using XDoclet

Using XDoclet is simple. Just as you write JavaDoc tags for your code (you do comment your code, don't you?), you now add XDoclet tags too. These tags are used by XDoclet as providers of meta-data that is then used to generate other files as required.

For a thorough example of how to use XDoclet, consult the samples. However, this page should give you enough of a start to XDoclet your code.

A typical XDoclet comment might look like this:

 * This is the Account entity bean. It is an example of how to use the
 * EJBDoclet tags.
 * @see Customer
 * @ejb.bean
 *     name="bank/Account"
 *     type="CMP"
 *     jndi-name="ejb/bank/Account"
 *     local-jndi-name="ejb/bank/LocalAccount"
 *     primkey-field="id"
 * @ejb.finder
 *     signature="java.util.Collection findAll()"
 *     unchecked="true"
 * @ejb.transaction
 *     type="Required"
 * @ejb.interface
 *     remote-class="test.interfaces.Account"
 * @ejb.value-object
 *     match="*"
 * @version 1.5

There are three parts to that comment: The comment, the javadoc tag, and the XDoclet tags. The first two are your standard documentation. Just because you are using XDoclet doesn't mean that you stop doing normal documentation. The third part of the comment is the part that we are interested in. An XDoclet tag is comprised of the following parts:

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

The concept is similar to an XML element, which has a tag name and an optional set of attributes. The difference is the syntax.

Tags are grouped by namespaces, and have names that are unique within that namespace. Tags can have zero or more attributes, which are grouped in name="value" pairs. Looking at the above example, we find the first tag is in the ejb namespace, and is called bean. The ejb.bean tag defines data relating to Enterprise Java Beans. Every EJB will require a name, and it is specified here. The namespace is a mechanism for making sure no name collision happens. Namespaces include ejb, web, jboss, weblogic, struts and so on. So it's simply a way to group related tags. For details on individual tags, consult the Tag Reference.

Tag values can be specified as ant properties. For example:

@jboss.create-table create="${jboss.create.table}"

Where the jboss.create.table is a property defined in the ant project. For more information on ant properties consult the Jakarta Ant documentation.

Tags exist at both class and method level (and in some rare cases even on the field or constructor level). As a general rule, if information can be determined by the name or type of a class, then it will be - and hence there will not be a requirement to specify that information with a tag. An example of this is the type attribute of the ejb.bean tag example above. The type in this instance refers to the Entity type (CMP or BMP), but if the class implemented the javax.ejb.SessionBean interface the type would be Stateful or Stateless. So in the above example, the type can be omitted.

To start using XDoclet you must first determine what it is you wish to use it for. The two most popular usages are EJBDoclet and WebDoclet. Generally you should define the XDoclet task for Ant, setup the configuration parameter. Here is an example:

<path id="project.class.path">
    <fileset dir="${lib.dir}">
        <include name="*.jar"/>

<target name="ejbdoclet" depends="prepare">

        <format property="TODAY" pattern="d-MM-yy"/>

        addedtags="@xdoclet-generated at ${TODAY}"
        <fileset dir="${java.dir}">
            <include name="**/*"/>


        <packageSubstitution packages="persistence" substituteWith="interfaces"/>

        <remoteinterface pattern="{0}Remote"/>
        <localinterface pattern="{0}"/>

        <homeinterface />


        <deploymentdescriptor destdir="${build.dir}/ejb/META-INF"/>
        <jboss version="3.0"
            datasourcemapping="Hypersonic SQL"

<target name="compile" depends="ejbdoclet">
   <!-- Compile EJBs -->
       includes="test/ejb/*.java, test/interfaces/*.java"

Here the compile target depends on the ejbdoclet target. This means that before compiling anything all home/local/remote interfaces, primary key, data-objects and deployment descriptors are generated. The first thing you have to do is define the ejbdoclet task for Ant.

To do so you use taskdef, where you specify xdoclet.modules.ejb.EjbDocletTask as the class implementing ejbdoclet task. Note that the classpathref points to the path with id "project.class.path". This path should have all XDoclet jar files and commons-logging.jar.

Next you declare ejbdoclet task, with a set of configuration parameters and nested elements. For example, destdir specifies where to put generated files. As you can see there's an inheritance mechanisms also, you can override this destdir parameter for each nested element (or as we call it sub-task).

<deploymentdescriptor/> does exactly that; put the generated ejb-jar.xml file somewhere else than where generated java sources for home/remote/pk/etc are placed. For a complete list of configurable parameters consult the Ant Task Reference for each task and sub-task.

By default each task has some built-in sub-tasks. Some of them are mandatory, for example <remoteinterface/> and <localinterface/>, can you imagine an EJB without a remote or local (EJB 2.0 only) interface? Some other tasks may be optional, for example <jboss/> is optional if you're not using JBoss Application Server.

There's even a third form of sub-tasks: <template/>. This is useful for cases where you want to design your own template file and generate a customized file. So, you need a simple way to let XDoclet use your template file. Here is an example:


    <fileset dir="${java.dir}">
        <include name="**/*"/>

So you put a <template/> element in the task, specify the path to your template file and output file name (which will we stored in the directory specified in destdir parameter). This is very useful for those creative people who want to easily take advantage of XDoclet's framework-like capabilities and define their own set of @tags and templates generating something from those @tags.

So whenever you build, ejbdoclet (and/or whatever other task) is run and generates up-to-date files.

Quick checklist of things to get XDoclet running:

  • Modify (creating if required) your build.xml script (see Jakarta Ant web site for details).
  • Add XDoclet tags to your source code.
  • Stop worrying about all that boring code you used to write! XDoclet does it all for you now.

The mailing lists provide a wealth of knowledge, and the developers are lurking on the xdoclet-user list, so feel free to ask questions, make suggestions, or just generally discuss XDoclet.