Introduction

MetaClass provides mechanisms via which users can selectively filter out JavaClass objects so that they will not be processed to produce MetaClass metadata files.

My First Interceptor

All filters implement the org.realityforge.metaclass.tools.compiler.JavaClassFilter interface. Consider the situation where a developer only wants to process JavaClass objects that have the doclet tag "@dna.component" declared at the class level. All other classes should be skipped as they are not used by the application and only increase the size of the generated metadata. The following source code performs that filtering. 

public class NonDNAComponentFilter
    implements JavaClassFilter
{
    public JavaClass filterClass( JavaClass javaClass )
    {
        if( null != javaClass.getTagByName( "dna.component" ) )
        {
            return javaClass;
        }
        else
        {
            return null;
        }
    }
}

Using the Filter

After the developer has written the filter they have to get the ant task to use the interceptor. This is done by adding a child element <filter/> into the task. This element has one attribute indicating the name of the filter class to use and contains a child <classpath/> element that defines where the .class files for filter are loaded from. See below for an example of how to use the above filter. Any number of Filters can be added and each filter will be invoked in turn until one returns null or until there are no more filter left. 

<metaclassGen destDir="target/classes">
    <fileset dir="src/java"/>
    <filter name="example.filter.NonDNAComponentFilter">
        <classpath>
            <pathelement location="myFilter.jar"/>
        </classpath>
    </filter>
</metaclassGen>