In this method of invocation we used the -nocompile to ensure that the source file specified isn't complied. The -classpath option specifies the classpath required by the processor. The -A option is ignored by the APT tool and is used by the annotation processor to get any specific processing-related information. In our case, we specified the location of the struts-config.xml in the file system.

The last step is to process the files with the annotation processor. Besides the command line, one could write an ANT Custom Task to generate the code. We strongly recommend that this be done. Since more and more projects are using ANT for automating the build process, it makes more sense to do an ANT build for automating code generation as well.

Writing an ANT task is easy and done by writing a custom task and extending the org.apache.tools.ant.Task class. Once that's done, the next step is to define the attributes and the corresponding setter methods for the attributes. The core processing logic is provided in the execute method called by the ANT framework. In our case, we delegate the bulk of the code generation work to the com.sun.tools.apt.main.Main class from the tools.jar. This is the actual byte code that's also used by the apt command line.

The following XML snippet from an ANT build shows how use the custom ANT task:

<taskdef name="apt" 
          classname="com.article.jdj.
           annotation.task.APTTask" >
   <classpath>
      <pathelement 
       location="F:\Article\Dev\Annotation\
        dist\Annotation.jar"/>
   </classpath>
</taskdef>
<target name="main">
<apt 	factory="com.jdj.article.gen.StrutsConfigGenerator"	
src="F:\Article\Dev\Annotation\src\com\jdj\article\
 action\*
          .java"
 	processorOption="struts-config=
        F: \Article\Dev\Annotation\generated\
         struts-config.xml" >
    <classpath>
    	<pathelement location="C:\Sun\AppServer\
      lib\j2ee.jar"/>
	<pathelement location="...">
    </classpath>
</apt>
</target>

Summary
In this article we introduced the idea of defining annotation types, how to use defined types as annotation and how to go about generating code or other supporting files based on annotation. This new and powerful technology is transforming the way we code. As more and more tools and products start using this facility, developers will realize improved quality in their code and a concomitant increase in productivity.

Resources

• Figure 1
• Table 1
• Table 2
• Source Code