Can I create an abstract class with byte buddy? about byte-buddy

[raphw]

Calling withoutCode creates an abstract method and a constructor cannot be abstract. Instead, you would need to call the Object class's default constructor. For this, you would need to implement approriate byte code. You can do this by creating a simple Instrumentation:

TypeDescription objectType = new TypeDescription.ForLoadedType(Object.class);
new Instrumentation.Simple(
  MethodVariableAccess.forType(objectType).loadFromIndex(0), 
  MethodInvocation.invoke(objectType.getDeclaredMethods().filter(isConstructor()).getOnly())
    .special(objectType),
  MethodReturn.VOID);

I recognize this use case and that this should be easier. I will add a utility instrumentation that makes this a one-liner in the future.

Also, you might want the type itself to be public what you did not specify.

[uvwild]

Thanks mate. It was working in the end:
Find all annotated classes:

    public static Set<Constructor> getSQLInjectedItemSubClassCtors() {
        Predicate<String> filter = new FilterBuilder().include("mycore.legacy.*")
                                                    .include("myother.legacy.core.*");
        Reflections reflections = new Reflections(new ConfigurationBuilder().filterInputsBy(filter)
                             .setScanners(
                                   new SubTypesScanner().filterResultsBy(filter), 
                                   new MethodAnnotationsScanner().filterResultsBy( filter), 
                                   new MethodParameterScanner()).setUrls( ClasspathHelper.forClassLoader()));
        Set<Constructor> annotated = reflections.getConstructorsAnnotatedWith(SQLInject.class);
        return annotated;
    }

Then create the mixin for them:

    public static Class<?> createMixinFor(final Class declaringClass) {
        assert(declaringClass != null);
        try {
            Annotation methodAnnotation = JacksonItemMixin.class.getDeclaredConstructor(Long.class).getAnnotation(JsonCreator.class);
            assert(methodAnnotation != null);
            Annotation parameterAnnotation = JacksonItemMixin.class.getDeclaredConstructor(Long.class).getParameterAnnotations()[0][0];
            assert(parameterAnnotation != null);
            LOG.debug("Annotation: {}",parameterAnnotation.annotationType());
            TypeDescription objectType = new TypeDescription.ForLoadedType(Object.class);
            Instrumentation instrumentation = new Instrumentation.Simple(MethodVariableAccess.forType(objectType).loadFromIndex(0), MethodInvocation.invoke(
                objectType.getDeclaredMethods().filter(ElementMatchers.isConstructor()).getOnly()).special(objectType), MethodReturn.VOID);
            Class<?> dynamicType = new ByteBuddy().withModifiers(TypeManifestation.ABSTRACT)
                                                  .subclass(Object.class, ConstructorStrategy.Default.NO_CONSTRUCTORS)
                                                  .name(declaringClass.getCanonicalName().concat("MixIn"))
                                                  .defineConstructor(Arrays.<Class<?>>asList(Long.class), Visibility.PROTECTED)
                                                  .intercept(instrumentation)
                                                  .annotateMethod(methodAnnotation)
                                                  .annotateParameter(0, parameterAnnotation)
                                                  .make()
                                                  .load(CachingItemFactory.class.getClassLoader(), ClassLoadingStrategy.Default.CHILD_FIRST_PERSISTENT)
                                                  .getLoaded();
            LOG.debug("created Mixin {} for {}", dynamicType, declaringClass);
            assert(dynamicType.getDeclaredConstructor(Long.class) != null);
            assert(dynamicType.getDeclaredConstructor(Long.class).getAnnotation(JsonCreator.class) != null);
            assert(dynamicType.getDeclaredConstructor(Long.class).getParameterAnnotations()[0][0] != null);
            return dynamicType;
        } catch (NoSuchMethodException nme) {
            LOG.error("createMixinFor: ", nme);
        }
        return null;
    }

Finally, use jackson mapper to apply this all:

        objectMapper = new ObjectMapper();
        // use generated Mixin Classes
        Set<Constructor> ctors = getSQLInjectedItemSubClassCtors();
        for (Constructor ctor : ctors) {
            // add mixin annotations for inheritance relationships
            Class<?> persistenceClass = ctor.getDeclaringClass();
            objectMapper.addMixInAnnotations(persistenceClass, createMixinFor(persistenceClass));
        }

[raphw]

Great, I would like to keep this issue open until I had the time to implement an instrumentation that makes this impler. Thanks for reporting and providing feedback.

[uvwild]

Oops sorry didn't want to disturb your work flow....

[raphw]

No worries. I appreciate the clean-up and the feedback. This just serves me as a reminder.

[raphw]

I implemented a MethodCall instrumentation that is included in the next version of Byte Buddy. You can then create the instrumentation by:

MethodCall.invoke(Object.class.getDeclaredConstructor())

This instrumentation also allows you to hand over parameters if you wanted to call a constructor that takes parameters.

[raphw]

This instrumentation is now implemented in the latest version and pushed to Maven Central.