SillyProcessor.java

package com.freemindcafe.apt.sample1;

import java.io.IOException;
import java.util.Set;

import javax.annotation.processing.AbstractProcessor;
import javax.annotation.processing.Filer;
import javax.annotation.processing.Messager;
import javax.annotation.processing.ProcessingEnvironment;
import javax.annotation.processing.RoundEnvironment;
import javax.annotation.processing.SupportedAnnotationTypes;
import javax.annotation.processing.SupportedSourceVersion;
import javax.lang.model.SourceVersion;
import javax.lang.model.element.Element;
import javax.lang.model.element.TypeElement;
import javax.tools.Diagnostic.Kind;
import javax.tools.JavaFileObject;

@SupportedAnnotationTypes(value= {"com.freemindcafe.apt.sample1.SillyMe"})
@SupportedSourceVersion(SourceVersion.RELEASE_6)
public class SillyProcessor extends AbstractProcessor { 

    private Filer filer;
    private Messager messager;

    @Override
    public void init(ProcessingEnvironment env) {
        filer = env.getFiler();
        messager = env.getMessager();
    }

    @Override
    public boolean process(Set<? extends TypeElement> elements, RoundEnvironment env) {
        
        for (Element element : env.getElementsAnnotatedWith(SillyMe.class)){
        //for (Element element : env.getRootElements()) {
            
            if (element.getSimpleName().toString().startsWith("Silly")) {
                // We don't want generate new silly classes 
                // for auto-generated silly classes
                continue;
            }

            if (element.getSimpleName().toString().startsWith("TestSilly")) {
                messager.printMessage(Kind.WARNING, 
                    "This class name starts with a T!", 
                    element);   
            }

            String sillyClassName = "Silly" + element.getSimpleName();
            String sillyClassContent = 
                    "package silly;\n" 
                +   "public class " + sillyClassName + " {\n"
                +   "   public String foobar;\n"
                +   "}";

            JavaFileObject file = null;

            try {
                file = filer.createSourceFile(
                        "silly/" + sillyClassName, 
                        element);
                file.openWriter()
                    .append(sillyClassContent)
                    .close();
            } catch (IOException e) {
                e.printStackTrace();
            }

        }

        return true;
    }
}