How to create a bytebuddy agent that intercepts a field setter from annotated field?

Question

What I am trying to do is basically match a class's field with an annotaion and them intercept the field's getter and setter.

 public class Foo { @Sensitive private String Blah;

Here is the code for my agent:

 private static AgentBuilder createAgent() { return new AgentBuilder .Default() .with(AgentBuilder.RedefinitionStrategy.RETRANSFORMATION) .type(ElementMatchers.is(FieldTypeMatcher.class).and(ElementMatchers.isAnnotatedWith(Foo.class))) .transform(((builder, typeDescription, classLoader, module) -> builder .method(method -> method.getActualName().contains(typeDescription.getActualName())) .intercept(Advice.to(Interceptor.class)) )); }

I though I could match the field's name with the method's signature but I had no luck.

Rafael Winterhalter · Accepted Answer · 2019-10-24 18:41:09Z

I assume that Foo has a getter and setter for Blah?

In this case, I recommend a custom ElementMatcher implementation such as:

class FieldMatcher implements ElementMatcher<MethodDescription> { @Override public boolean matches(MethodDescription target) { String fieldName; if (target.getName().startsWith("set") || target.getName().startsWith("get")) { fieldName = target.substring(3, 4).toLowerCase() + target.substring(4); } else if (target.getName().startsWith("is")) { fieldName = target.substring(2, 3).toLowerCase() + target.substring(3); } else { return false; } target.getDeclaringType() .getDeclaredFields() .filter(named) .getOnly() .getDeclaredAnnotations() .isAnnotationPresent(Sensitive.class); } }

This matcher checks if a method is a getter or setter, locates the corresponding field and checks for the annotation being present on it.

Hi Rafael, thank you so much for answering so fast! I get the gist of what you're doing, although my IDE tells me that it can't resolve .isAnnotationPresent. I'm using bytebuddy 1.10.1 should I be using a different version?

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