Adding a declaresMethod matcher to a AgentBuilder#type matcher makes method matchers fail

I’d like to use declaresMethod matchers before hasSuperType matchers in order to pre-filter classes that don’t declare the method I want to instrument before applying the hasSuperType matcher, which is more expensive.

Unfortunately, using the declaresMethod matcher seems to mess with the method matcher (net.bytebuddy.agent.builder.AgentBuilder.Transformer.ForAdvice#advice(net.bytebuddy.matcher.ElementMatcher<? super net.bytebuddy.description.method.MethodDescription>, java.lang.String))

Example: https://github.com/elastic/apm-agent-java/blob/6d4a28535d822f731a227ec026e597d57629e801/apm-agent-plugins/apm-servlet-plugin/src/main/java/co/elastic/apm/servlet/AsyncInstrumentation.java#L75-L77

When adding .and(declaresMethod(any())) after line 76, the test co.elastic.apm.servlet.AsyncServletTest#testAsync fails. The logs tell me that I still get a type match, but I don’t get a method match anymore.

[raphw]

I see that can be a problem, especially in small environments, but in the end its a trade off between speed and memory as in any application.

[yaohwu]

I see, the problem is class loading circularities. If you load a class during a class file transformation, this class will not be transformed. As a matter of fact, Byte Buddy has a mechanism for that, called a CircularityLock to suppress any class loading that occurs during a transformation. If it did not do this, the JVM would yield a CircularityError if the currently transformed class was reached via the load chain.

To avoid this, you need to avoid all class loading, for example by using Byte Buddy’s pool-only descriptor strategy where the library parses byte code even if a loaded class is available.

Same problem happened to my project. My plan is to call target.getDeclaredTypes() and target.getDeclaredFields() to load all the classes used by the target class during the matcher executing. But it did not work. Is the matcher-excuting a part of the class file transformation? @raphw

So that I have to make another way to load the class before actual class-transformation. A empty class file transformer installed for loading class as the last solution. Here is the demo.

Cause I can not load class by the class name for some reasons, so it works perfect for me. Is there more effective and elegant way?