[Q] How to remove/replace existing annotation

[michelkaeser]

Is there a way to replace (or remove so it can be re-added) an existing annotation from a type?

Let's say the input is:

@PersistenceCapable
class X {}

and I want

@PersistenceCapable(value="", key="")
class X {}

How would I do that?

A simple annotateType makes the annotation appear twice.

Thanks!

[raphw]

It is possible but a bit tricky, there is not yet a good API for such transformations. The problem is that Byte Buddy cannot generally know if a value is represented as a default value or if it is explicitly defined but to this default value. It sounds irrellevant but as a matter of fact, it does matter for (too manny) applications.

I hopefully can add better support for this in the future. For now, using ASM is the easiest way of getting this done.

[thekingn0thing]

@raphw did you find a time to add API for removing annotation?

[raphw]

Not yet, unfortunately. I use this issue to track the progress. With modules and the sun.misc.Unsafe cleanup, I did not had much time for features recently.

[albanf]

Hi, I am new to byte buddy, and I am trying to modify the value of an annotation in an agent.
When you say

For now, using ASM is the easiest way of getting this done.

do you mean that it's possible to do this when transforming a class in an agent? I couldn't find any example of a transformer for that case.

What I am trying to do is to transform:

@MessageDriven(
        activationConfig = {
                @ActivationConfigProperty(
                        propertyName = "resourceAdapter",
                        propertyValue = "jmsra")
        }
)
public class MyClass {
}

and change the value of propertyValue

@MessageDriven(
        activationConfig = {
                @ActivationConfigProperty(
                        propertyName = "resourceAdapter",
                        propertyValue = "activemq-rar")
        }
)
public class MyClass {
}

The agent is correctly setup and processes the class:

new AgentBuilder.Default()
                .type(ElementMatchers.<TypeDescription>isAnnotatedWith(MessageDriven.class))
                .transform(new ChangeResourceAdapterTransformer())
                .with(AgentBuilder.Listener.StreamWriting.toSystemOut())
                .with(AgentBuilder.TypeStrategy.Default.REDEFINE)
                .installOn(inst);

But I don't know what to do in the transformer, since annotateType is creating a duplicate like mentioned before:

public DynamicType.Builder<?> transform(DynamicType.Builder<?> builder, TypeDescription typeDescription, ClassLoader classLoader, JavaModule javaModule) {

        return builder
                .annotateType(AnnotationDescription.Builder.ofType(MessageDriven.class)
                        .defineAnnotationArray("activationConfig", new TypeDescription.ForLoadedType(ActivationConfigProperty.class),
                                AnnotationDescription.Builder.ofType(ActivationConfigProperty.class)
                                        .define("propertyName", "resourceAdapter")
                                        .define("propertyValue", "activemq-rar")
                                        .build())
                        .build());
    }

Thanks for your help!

[raphw]

As mentioned, it is not currently possible to remove the existing annotation. This is not currently solved fully satisfactory in Byte Buddy such that you have to reapply all annotations what means filtering out the first annotation using an AsmClassVisitorWrapper where the second one is picked up correctly.

[albanf]

Do you have an example of a visitor which would remove that annotation (or all annotations?). At least for some use case, where you can rebuild the whole annotation or set of annotations, that would work.

[raphw]

Basically, you need to implement a MethodVisitor that returns null on any annotation you want to remove. You can register such a visitor using a custom instance of AsmVisitorWrapper.

[raphw]

Closing this in favor of #917