/**
 * Created by mkhwang on 2021/04/20
 * Email : orange2652@gmail.com
 * Github : http://github.com/myeongkwonhwang
 */
public class MagicMojaProcessor extends AbstractProcessor {

    //이 Processor가 어떤 Annotation을 처리할 것인가.
    @Override
    public Set<String> getSupportedAnnotationTypes() {
        return Set.of(Magic.class.getName());
    }

    //어떠한 소스코드 Version을 지원할 것인지.
    @Override
    public SourceVersion getSupportedSourceVersion() {
        return super.getSupportedSourceVersion();
    }

    @Override
    public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
        Set<? extends Element> elements = roundEnv.getElementsAnnotatedWith(Magic.class);
        for (Element element : elements) {
            Name elementName = element.getSimpleName();
            if(element.getKind() != ElementKind.INTERFACE) { //Element Type이 Interface가 아니라면
                processingEnv.getMessager().printMessage(Diagnostic.Kind.ERROR, "me.mkhwang.Magic annotation can not be used" + elementName);
            } else { //Logging만
                processingEnv.getMessager().printMessage(Diagnostic.Kind.NOTE, "Processing" + elementName);
            }
        }
        return true;
    }

}

<dependency>
      <groupId>com.google.auto.service</groupId>
      <artifactId>auto-service</artifactId>
      <version>1.0-rc7</version>
</dependency>

@AutoService(Processor.class)
public class MagicMojaProcessor extends AbstractProcessor {
	...
}

<dependency>
    <groupId>com.squareup</groupId>
    <artifactId>javapoet</artifactId>
    <version>1.9.0</version>
</dependency>

@AutoService(Processor.class)
public class MagicMojaProcessor extends AbstractProcessor {

    //이 Processor가 어떤 Annotation을 처리할 것인가.
    @Override
    public Set<String> getSupportedAnnotationTypes() {
        return Set.of(Magic.class.getName());
    }

    //어떠한 소스코드 Version을 지원할 것인지.
    @Override
    public SourceVersion getSupportedSourceVersion() {
        return super.getSupportedSourceVersion();
    }

    @Override
    public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
        Set<? extends Element> elements = roundEnv.getElementsAnnotatedWith(Magic.class);
        for (Element element : elements) {
            Name elementName = element.getSimpleName();
            if(element.getKind() != ElementKind.INTERFACE) { //Element Type이 Interface가 아니라면
                processingEnv.getMessager().printMessage(Diagnostic.Kind.ERROR, "me.mkhwang.Magic annotation can not be used" + elementName);
            } else { //Logging만
                processingEnv.getMessager().printMessage(Diagnostic.Kind.NOTE, "Processing" + elementName);
            }

            TypeElement typeElement = (TypeElement)element;
            ClassName className = ClassName.get(typeElement);

            //method생성
            MethodSpec pullOut = MethodSpec.methodBuilder("pullOut") //method name
                    .addModifiers(Modifier.PUBLIC)                          //modifier
                    .returns(String.class)                                  //return type
                    //.addParameter()                                       //arg
                    .addStatement("return $S", "Rabbit!")
                    .build();

            //class생성
            TypeSpec magicMoja = TypeSpec.classBuilder("MagicMoja")
                    .addModifiers(Modifier.PUBLIC)
                    .addSuperinterface(className)
                    .addMethod(pullOut)
                    .build();

            //AbstractProccessor를 상속받은 class에서 사용할 수 있는 protected변수
            //소스코드, 클래스 코드 및 리소스를 생성할 수 있는 인터페이스
            Filer filer = processingEnv.getFiler();

            try {
                JavaFile.builder(className.packageName(), magicMoja)
                        .build()
                        .writeTo(filer);
            } catch (IOException e) {
                processingEnv.getMessager().printMessage(Diagnostic.Kind.ERROR, "FATAL ERROR: " + e);
            }
        }
        return true;
    }

}

@Magic
public interface Moja {

    String pullOut();
}

public class App {
    public static void main(String[] args) {
        Moja moja = new MagicMoja();
        System.out.println(moja.pullOut());
    }
}