[Question] How to advice a class that have been intercepted by another javaagent but not loaded

[WangSZ]

[com.web.TestController] is intercepted by another javaagent and not loaded. Its not working when I advice it.

[Byte Buddy] ERROR com.web.TestController [jdk.internal.loader.ClassLoaders$AppClassLoader@2d8e6db6, unnamed module @29412871, loaded=false]
java.lang.IllegalStateException: Cannot resolve type description for com.web.TestController$auxiliary$yX8NWW70
at net.bytebuddy.pool.TypePool$Resolution$Illegal.resolve(TypePool.java:159)
	at net.bytebuddy.pool.TypePool$Default$WithLazyResolution$LazyTypeDescription.delegate(TypePool.java:914)
	at net.bytebuddy.description.type.TypeDescription$AbstractBase$OfSimpleType$WithDelegation.getModifiers(TypeDescription.java:8122)
	at net.bytebuddy.description.ModifierReviewable$AbstractBase.matchesMask(ModifierReviewable.java:618)
	at net.bytebuddy.description.ModifierReviewable$AbstractBase.isPublic(ModifierReviewable.java:336)
	at net.bytebuddy.description.type.TypeDescription$AbstractBase.isVisibleTo(TypeDescription.java:7631)
	at net.bytebuddy.matcher.VisibilityMatcher.matches(VisibilityMatcher.java:48)
	at net.bytebuddy.matcher.VisibilityMatcher.matches(VisibilityMatcher.java:27)
	at net.bytebuddy.matcher.NegatingMatcher.matches(NegatingMatcher.java:46)
	at net.bytebuddy.matcher.ErasureMatcher.matches(ErasureMatcher.java:50)
	at net.bytebuddy.matcher.ErasureMatcher.matches(ErasureMatcher.java:29)
	at net.bytebuddy.matcher.MethodParameterTypeMatcher.matches(MethodParameterTypeMatcher.java:48)
	at net.bytebuddy.matcher.MethodParameterTypeMatcher.matches(MethodParameterTypeMatcher.java:27)
	at net.bytebuddy.matcher.CollectionItemMatcher.matches(CollectionItemMatcher.java:48)
	at net.bytebuddy.matcher.CollectionItemMatcher.matches(CollectionItemMatcher.java:26)
	at net.bytebuddy.matcher.NegatingMatcher.matches(NegatingMatcher.java:46)
	at net.bytebuddy.matcher.MethodParametersMatcher.matches(MethodParametersMatcher.java:49)
	at net.bytebuddy.matcher.MethodParametersMatcher.matches(MethodParametersMatcher.java:28)
	at net.bytebuddy.matcher.ElementMatcher$Junction$Conjunction.matches(ElementMatcher.java:122)
	at net.bytebuddy.matcher.ElementMatcher$Junction$Conjunction.matches(ElementMatcher.java:122)
	at net.bytebuddy.matcher.ElementMatcher$Junction$Conjunction.matches(ElementMatcher.java:122)
	at net.bytebuddy.matcher.FilterableList$AbstractBase.filter(FilterableList.java:125)
	at net.bytebuddy.dynamic.scaffold.MethodRegistry$Default.prepare(MethodRegistry.java:505)
	at net.bytebuddy.dynamic.scaffold.inline.RedefinitionDynamicTypeBuilder.make(RedefinitionDynamicTypeBuilder.java:198)
	at net.bytebuddy.agent.builder.AgentBuilder$Default$Transformation$Simple$Resolution.apply(AgentBuilder.java:10123)
	at net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer.doTransform(AgentBuilder.java:10494)
	at net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer.transform(AgentBuilder.java:10457)
	at net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer.access$1500(AgentBuilder.java:10223)
	at net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer$Java9CapableVmDispatcher.run(AgentBuilder.java:10907)
	at net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer$Java9CapableVmDispatcher.run(AgentBuilder.java:10845)
	at java.base/java.security.AccessController.doPrivileged(Native Method)
	at net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer.transform(AgentBuilder.java:10413)
	at net.bytebuddy.agent.builder.AgentBuilder$Default$ExecutingTransformer$ByteBuddy$ModuleSupport.transform(Unknown Source)

[raphw]

For your initial agent, you are injecting additional classes which are based on top of synthetic classes which are not resolvable as the class loader cannot read their class file representations.

If you want to write agents that are stackable, I recommend you to use Advice rather then MethodDelegation as it aims to enrich methods rather then replacing them.

Otherwise, you'd need to capture the byte code implementations you generate using an AgentBuilder.Listener and implement a ClassFileLocator that looks up these altered class files.

[WangSZ]

For your initial agent, you are injecting additional classes which are based on top of synthetic classes which are not resolvable as the class loader cannot read their class file representations.

If you want to write agents that are stackable, I recommend you to use Advice rather then MethodDelegation as it aims to enrich methods rather then replacing them.

Otherwise, you'd need to capture the byte code implementations you generate using an AgentBuilder.Listener and implement a ClassFileLocator that looks up these altered class files.

Thanks a lot and I`ll try a ClassFileLocator

[reallax]

Otherwise, you'd need to capture the byte code implementations you generate using an AgentBuilder.Listener and implement a ClassFileLocator that looks up these altered class files.

Hi, I'm new to bytebuddy, is there any demo for the quote above?

[raphw]

No, but in the listener, in the onTransform method, you receive names and byte codes of any transformed classes within the DynamicType instance provided. You would need to extract that data and make it available via the ClassFileLocator which provides names where the byte code of the classes previously supplied to the listener would be expected in return.