Got an issue: java.lang.ClassFormatError: Duplicate method name "listIterator"

[satoshi hikida]

Hi,

I'm creating a simple tool using Byte Buddy to trace method calls.
While testing it on an application that uses the Guava library's `ImmutableList`, I encountered the following `java.lang.ClassFormatError`.

``` shell
$ ./gradlew run
Reusing configuration cache.

> Task :app:run FAILED
premain!! arges:null
tracer start!!
org.example.App#main :: is called.
tracer end!!
Exception in thread "main" java.lang.ClassFormatError: Duplicate method name "listIterator" with signature "(I)Ljava.util.ListIterator;" in class file com/google/common/collect/ImmutableList$ReverseImmutableList
        at java.base/java.lang.ClassLoader.defineClass1(Native Method)
        at java.base/java.lang.ClassLoader.defineClass(ClassLoader.java:1027)
        at java.base/java.security.SecureClassLoader.defineClass(SecureClassLoader.java:150)
        at java.base/jdk.internal.loader.BuiltinClassLoader.defineClass(BuiltinClassLoader.java:862)
        at java.base/jdk.internal.loader.BuiltinClassLoader.findClassOnClassPathOrNull(BuiltinClassLoader.java:760)
        at java.base/jdk.internal.loader.BuiltinClassLoader.loadClassOrNull(BuiltinClassLoader.java:681)
        at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:639)
        at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)
        at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:526)
        at org.example.App.main$original$LSGQf8fD(App.java:16)
        at org.example.App.main(App.java)

FAILURE: Build failed with an exception.
...
```

Is there a way to work around this issue?  

I would greatly appreciate any advice.  

For reference, my execution environment is as follows:
- OS: macOS Ventura (version 13.4)
- Java: OpenJDK version 21.0.6 2025-01-21 LTS

Here is the sample application code.
```
import com.google.common.collect.ImmutableList;

public class App {
  public static void main(String[] args) {
    ImmutableList<String> alist = ImmutableList.of("a", "b", "c");
    System.out.println(alist.get(0));
  }
}
```

And here is the `build.gradle` file.
```
plugins {
    id 'application'
}

repositories {
    mavenCentral()
}

dependencies {
    implementation libs.guava
}

java {
    toolchain {
        languageVersion = JavaLanguageVersion.of(21)
    }
}

application {
    mainClass = 'org.example.App'
    applicationDefaultJvmArgs = ["-javaagent:../my-tracer-all.jar"]
}
```

Here is the code for the tracing tool.
```java
package org.example;

import java.lang.instrument.Instrumentation;
import java.lang.reflect.Method;
import net.bytebuddy.agent.builder.AgentBuilder;
import net.bytebuddy.implementation.MethodDelegation;
import net.bytebuddy.implementation.SuperMethodCall;
import net.bytebuddy.implementation.bind.annotation.Origin;
import net.bytebuddy.implementation.bind.annotation.RuntimeType;
import net.bytebuddy.matcher.ElementMatchers;

public class TraceAgent {
  public static void premain(String args, Instrumentation instrumentation) {
    System.out.println("premain!!");

    AgentBuilder agentBuilder =
        new AgentBuilder.Default()
            .type(ElementMatchers.any())
            .transform(
                (builder, typeDescription, classLoader, module, protectionDomain) ->
                    builder
                        .method(ElementMatchers.any())
                        .intercept(
                            MethodDelegation.to(MethodLogger.class)
                                .andThen(SuperMethodCall.INSTANCE)));
    agentBuilder.with(AgentBuilder.Listener.StreamWriting.toSystemError());
    agentBuilder.installOn(instrumentation);
  }

  public static class MethodLogger {
    @RuntimeType
    public static void onMethodEnter(@Origin Method method) {
      System.out.println("tracer start!!");
      try {
        StackTraceElement[] stackTrace = Thread.currentThread().getStackTrace();

        StackTraceElement caller = null;
        if (stackTrace.length > 3) {
          caller = stackTrace[3];
        }

        if (caller != null) {
          System.out.printf(
              "caller::%s#%s (%s:%d), callee::%s#%s\n",
              caller.getClassName(),
              caller.getMethodName(),
              caller.getFileName(),
              caller.getLineNumber(),
              method.getDeclaringClass().getCanonicalName(),
              method.getName());

        } else {
          System.out.printf(
              "%s#%s :: is called.\n",
              method.getDeclaringClass().getCanonicalName(), method.getName());
        }
      } catch (Exception e) {
        System.out.println("An exception occurred: " + e.getMessage());
      }
      System.out.println("tracer end!!");
    }
  }
}
```

Best regards,
Satoshi Hikida

[Rafael Winterhalter]

That is strange. I can look into it if you created a reproducer. I assume that Google already manipulate the class file in a way. For mere decoration, Advice and .visit are normally a better option.

Best regards, Rafael

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[satoshi hikida]

Hi, Rafael

Thank you for your reply.

I've created the reproducer as a GitHub repository. Please refer to it.
https://github.com/reddikih/bd-issue

Please let me know if there are any better ways to set up a reproducer.

> For mere decoration, Advice and .visit are normally a better option.

I see. It may be more suitable for my purpose. I'll try that one as well. Thank you.

Best regards,
Satoshi Hikida

[Rafael Winterhalter]

This seems like a bug. I understand it such that Byte Buddy tries to generate bridge methods, which are missing, but also instruments the methods. I will need to see how I can avoid this.

To view this discussion visit https://groups.google.com/d/msgid/byte-buddy/4a284a01-f4d8-422b-a53c-5b4508f2ac2bn%40googlegroups.com.

[Rafael Winterhalter]

The Guava class declares some bridges that are of the wrong return type what is strange. As a consequence, Byte Buddy does not discover the previous declaration and declares the bridges again. I will need to add some mechanism that suppresses this.

[Rafael Winterhalter]

I think I found a fix. Could you run things with the latest master change set? You have to build Byte Buddy for this. I tried it and it seems to work. If you do not have any objections, this will be part of the next release.

Cheers, Rafael

[satoshi hikida]

I've tried re-run the reproducer with the master branch of the ByteBuddy, and confirmed it completed successfully.

I also tried to run another application, for which I found this issue the first time, and it completed successfully, too.

Thank you for the quick fix!!

Regards,

Satoshi

Appendix. Here is the execution log.
```

$ java -javaagent:agent/build/libs/my-agent-all.jar -jar app/build/libs/app-all.jar
premain!!
tracer start
issue.example.Main#main :: is called.
tracer end
tracer start
com.google.common.collect.ObjectArrays#checkElementsNotNull :: is called.
tracer end
tracer start
com.google.common.collect.ObjectArrays#checkElementsNotNull :: is called.
tracer end
tracer start
com.google.common.collect.ObjectArrays#checkElementNotNull :: is called.
tracer end
tracer start
com.google.common.collect.ObjectArrays#checkElementNotNull :: is called.
tracer end
tracer start
com.google.common.collect.ObjectArrays#checkElementNotNull :: is called.
tracer end
tracer start
com.google.common.collect.RegularImmutableList#get :: is called.
tracer end
a
```