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I want to intercept a static method call in What am I missing to instrument a class of the bootstrap class loader?
public class Main {
//
// gw -p genthreadname/ clean shadowJar
// java -javaagent:genthreadname/build/libs/genthreadname.jar -jar genthreadname/build/libs/genthreadname.jar
//
public static void main(String[] args) throws Exception {
System.out.println("main.genThreadName() = " + genThreadName());
new Thread(() -> System.out.println("Thread.currentThread().getName() = " + Thread.currentThread().getName())).start();
}
static String genThreadName() {
return "test";
}
}
public class ThreadInstrumentationAgent {
public static void premain(@SuppressWarnings("unused") String agentArgs, Instrumentation inst) {
new AgentBuilder.Default()
.ignore(ElementMatchers.none())
.with(InitializationStrategy.NoOp.INSTANCE)
.with(RedefinitionStrategy.RETRANSFORMATION)
.with(RedefinitionStrategy.DiscoveryStrategy.Reiterating.INSTANCE)
.type((RawMatcher) (typeDescription, classLoader, module, classBeingRedefined, protectionDomain) -> {
String name = typeDescription.getName();
if ("java.lang.Thread".equals(name)) {
// if ("test.Main".equals(name)) { // works
return true;
}
return false;
})
.transform(new AgentBuilder.Transformer.ForAdvice()
.with(AgentBuilder.LocationStrategy.ForClassLoader.WEAK)
.include(Thread.class.getClassLoader())
.with(Assigner.DEFAULT)
.withExceptionHandler(new Advice.ExceptionHandler.Simple(Removal.SINGLE))
.advice(ElementMatchers.named("genThreadName"), ThreadGenThreadNameInterceptor.class.getName()))
.installOn(inst);
System.out.println("...premain done");
}
}
class ThreadGenThreadNameInterceptor {
@Advice.OnMethodExit
public static void enter(@Advice.Origin Method method) {
System.out.println(".intercepted " + method);
new RuntimeException().printStackTrace();
}
} |
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Answered by
raphw
Jun 6, 2025
Replies: 1 comment 3 replies
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I get the following error when I enable logging with: .with(AgentBuilder.Listener.StreamWriting.toSystemError().withTransformationsOnly())
.with(AgentBuilder.InstallationListener.StreamWriting.toSystemError()) |
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3 replies
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I got it working by replacing the lines .transform(new AgentBuilder.Transformer.ForAdvice()
.with(AgentBuilder.LocationStrategy.ForClassLoader.WEAK)
.include(Thread.class.getClassLoader())
.with(Assigner.DEFAULT)
.withExceptionHandler(new Advice.ExceptionHandler.Simple(Removal.SINGLE))
.advice(ElementMatchers.named("genThreadName"), ThreadGenThreadNameInterceptor.class.getName()))with .transform((builder, typeDescription, classLoader, module, protectionDomain) -> builder
.visit(Advice.to(ThreadGenThreadNameInterceptor.class).on(ElementMatchers.named("genThreadName"))))What is the reason why the workaround is not running into the |
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Is there a way to use an |
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When using On this note, |
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Answer selected by
arouel
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When using
AgentBuilder.Transformer.ForAdvice(), Byte Buddy will try to load the class file directly to render a description of the advice, without loading it. By usingAdvice.to(ThreadGenThreadNameInterceptor.class), the description is rendered using Java reflection.On this note,
.include(Thread.class.getClassLoader())seems to be incorrect. Here you should include your agent's class loader that contains the advice classes. This is likely the real issue of your initial solution.