Replace one field with another in a method

Question

I'm trying to dynamically replace in a method body a field reference by another field reference. is that possible with bytebuddy?

The class I like to transform is like this:

public class TestReplace {
    @replace
    int a = 1;
    int b = 2;

    public int printA() {
        return a;
    }

    public int printB() {
        return b;
    }
}

The transformation consists in replacing the variables marked with @replace in the methods that visit them. The replacement will be done by variables that I will insert.

The class already transformed should look like this:

public class TestReplace {
    @replace
    int a = 1;
    int ___a = a * 10; // var inserted
    int b = 2;

    public int printA() {
        return ___a;
    }

    public int printB() {
        return b;
    }
}

I am new to the subject and would appreciate any help you could give me.

Thanks in advance

Answer 1

Yes, this is possible using MemberSubstitution :

MemberSubstitution.relaxed()
  .field(ElementMatchers.named("a"))
  .onRead()
  .doReplaceWith(otherField)

You can, for example, apply this transformation from a Java agent that you define using the AgentBuilder API. You probably also need to define the alternative field from this agent. You can reference this field using a FieldDescription.Latent .