从检测方法调用自己的类时，Java NoClassDefFoundError [英] Java NoClassDefFoundError when calling own class from instrumented method

问题描述

我正在研究一套简单的Java代理，以帮助我（并希望其他人）对Java应用程序进行故障排除。我想创建的一个代理工具JComponent.getToolTipText（）方法通过将鼠标光标悬停在它上面来快速识别任何GUI类。

I am working on a kit of simple Java agents to help me (and hopefully others) troubleshoot Java applications. One of the agents I would like to create instruments the JComponent.getToolTipText() method to quickly identify any GUI class by just hovering the mouse cursor over it.

你可以找到我的变压器的代码和项目的其余部分：

You can find the code of my transformer and the rest of the project here:

http://sfn.cvs.sourceforge.net/viewvc/sfn/core/src/main /java/org/leplus/sfn/transformer/JComponentTransformer.java?view=markup

我使用附件代理启动我的测试GUI，如下所示： / p>

I launch my test GUI with the agent attached as follow:

$ java -javaagent:target/jars/sfn-0.1-agent.jar=JComponent -cp lib/jars/bcel-5.2.jar:target/jars/sfn-0.1-test.jar:target/jars/sfn-0.1-agent.jar org.leplus.sfn.test.Main

sfn-0.1-agent.jar包含org.leplus.sfn.transformer.JComponentTransformer类。
sfn-0.1-test.jar包含org.leplus.sfn.test.Main类。

sfn-0.1-agent.jar contains the org.leplus.sfn.transformer.JComponentTransformer class. sfn-0.1-test.jar contains the org.leplus.sfn.test.Main class.

以下是应用程序在启动它时打印的内容我把鼠标放在它上面：

Here is what the application prints when I launch it and I put the mouse over it:

Loading agent: JComponent
Instrumentation ready!
Exception in thread "AWT-EventQueue-0" java.lang.NoClassDefFoundError: org/leplus/sfn/tracer/ComponentTracer
 at javax.swing.JComponent.getToolTipText(JComponent.java)
 at javax.swing.ToolTipManager$insideTimerAction.actionPerformed(ToolTipManager.java:662)
...

令人惊讶的是我是如果我改变我的变压器来从JRE调用任何类，它是有效的。但是当我调用自己的类org.leplus.sfn.tracer.ComponentTracer时它不起作用。我的第一个猜测是类路径问题，但ComponentTracer既在类路径中，也在代理程序的jar中。所以我迷路了。

What is surprising to me is that if I change my transformer to call any class from the JRE, it works. But it doesn't work when I call my own class org.leplus.sfn.tracer.ComponentTracer. My first guess was a classpath issue but the ComponentTracer is both in the classpath and in the agent's jar. So I am lost.

如果你们中的任何人看到我遗失的地方。

If any of you see where I am missing something.

干杯，

Tom

推荐答案

这是一个类加载器问题。您正在检测由引导类加载器管理的类（javax.swing.JComponent），并让它引用由系统类加载器管理的类（org.leplus.sfn.tracer.ComponentTracer）。

It's a class loader issue. You're instrumenting a class (javax.swing.JComponent) managed by the bootstrap class loader, and having it refer to a class (org.leplus.sfn.tracer.ComponentTracer) managed by the system class loader.

如果你将ComponentTracer类放在bootstrap类加载器中，问题就会消失。

If you put your ComponentTracer class in the bootstrap class loader, the problem should disappear.

java -Xbootclasspath/p:<path/to/jar/containing/ComponentTracer> -javaagent:...

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