Return value if matches condition or call original method

[KinComet]

Hi. I want to introduce a cache system here but I cannot find a way to inject my code.

    public static class Inject {
        @Advice.OnMethodEnter(skipOn = String.class)
        public static String met() {
            if (System.currentTimeMillis() > 0) { // If has cache (matches condition)
                return "inject";
            }
            // Call original method, else
            return null;
        }
    }

using

        ByteBuddyAgent.install(ByteBuddyAgent.AttachmentProvider.DEFAULT);
        new ByteBuddy().redefine(Source.class)
                .visit(Advice.to(Inject.class).on(ElementMatchers.named("test")))
                .make().load(Main.class.getClassLoader(), ClassReloadingStrategy.fromInstalledAgent());
        System.out.println(new Source().test()); // returns null but not the value inject method returns

Also tried MethodDelegation, but @SuperCall and @DefaultCall gives null, so I cannot call original method

[raphw]

Have you tried to set -Dnet.bytebuddy.dump=/some/folder?

You can then investigate the generated class to see if it actually contains the new code using javap. If you set @Advice.OnMethodEnter(skipOn = String.class, inline = false) you might also be able to set a break point. If it never triggers, something else is wrong.

[KinComet]

Have you tried to set -Dnet.bytebuddy.dump=/some/folder?

You can then investigate the generated class to see if it actually contains the new code using javap. If you set @Advice.OnMethodEnter(skipOn = String.class, inline = false) you might also be able to set a break point. If it never triggers, something else is wrong.

Looked into the dump, it's

    public String test() {
        if ((System.currentTimeMillis() > 0 ? "inject" : null) instanceof String) {
            return null;
        }
        return "test";
    }

It returns null, but not inject String.

[KinComet]

I could skip original method codes and add a OnMethodExit, but it adds one more of condition check. It will take more time. If all things can be done in OnMethodEnter or something like that, it would be great.

[raphw]

Indeed, now I understand what you are trying to do. You would need to add the following:

@Advice.OnMethodExit
static void exit(@Advice.Enter String enter, @Advice.Return(readOnly = false) String returned) {
  if (enter != null) {
    returned = enter;
  }
}

Otherwise, you will not assign the returned value.

[KinComet]

This works! Thank you so much.