Custom Annotations - replace annotation with custom code

Question

I want to create my own annotation processor. I'm as fas as that I registered my processor but am stuck now at the point of replacing the annotated function with the real functions code.

I want generate something simple like following:

public void onTest(Test data)
{
}

With an annotation like following:

// Annotation
@HandleEvent(Test.class)

My AbstractProcessor looks like following so far:

@SupportedAnnotationTypes("HandleEvent")
public class AnnotationProcessor extends AbstractProcessor
{
    @Override
    public synchronized void init(ProcessingEnvironment env)
    {
    }

    @Override
    public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv)
    {
        for (Element element : roundEnv.getElementsAnnotatedWith(HandleEvent.class))
        {
            HandleEvent annotation = element.getAnnotation(HandleEvent.class);
            Class clazz = annotation.value();

            String functionName = clazz.getName().replaceAll("\\.", "");

            StringBuilder sb = new StringBuilder();
            sb.append("public void ").append(functionName).append("(").append(clazz.getName()).append(" data)").append("\n");
            sb.append("{");
            sb.append("}");

            // How can I create a function in code with the above created string???
            // What do I have to do know and where should I write the function code into???
        }
        return true;
    }
}

What do I have to do next to really generate the class with the generated functions in it?