How do you use Java 1.6 Annotation Processing to perform compile time weaving?

Question

I have created an annotation, applied it to a DTO and written a Java 1.6 style annotationProcessor. I can see how to have the annotationProcessor write a new source file, which isn't what I want to do, I cannot see or find out how to have it modify the existing class (ideally just modify the byte code). The modification is actually fairly trivial, all I want the processor to do is to insert a new getter and setter where the name comes from the value of the annotation being processed.

My annotation processor looks like this;

@SupportedSourceVersion(SourceVersion.RELEASE_6)
@SupportedAnnotationTypes({ "com.kn.salog.annotation.AggregateField" })
public class SalogDTOAnnotationProcessor extends AbstractProcessor {

    @Override
    public boolean process(final Set<? extends TypeElement> annotations, final RoundEnvironment roundEnv) {
        //do some stuff
    }
}

Answer 1

By design, the annotation processing facility does not allow direct modification of the source code being processed. However, one can generate subclasses of the type being processed or the superclass of the type being processed. With some planning, this does allow some of the effect of modifying the type in question. I've written up an example of how this can fit together; see this blog entry for a more detailed explanation and some sample code.