[jboss-user] [Javassist user questions] - javassist.CannotCompileException: by java.lang.LinkageError:

[arsami]

Hi,

I am trying to change a class on-the-fly with this small program:


  |         Hello h = new Hello();
  |         h.say();
  |         ClassPool cp = new ClassPool(true);
  |         CtClass cc = cp.get("com.blabla.test.Hello");
  |         CtMethod m = cc.getDeclaredMethod("say");
  |         m.insertBefore("{ System.out.println(\"Hello.say():\"); }");
  |         Class c = cc.toClass();
  |         h = (Hello)c.newInstance();
  |         h.say();

and I get the following exception:


  | javassist.CannotCompileException: by java.lang.LinkageError: duplicate class definition:
  | 	at javassist.ClassPool.toClass(ClassPool.java:953)
  | 	at javassist.ClassPool.toClass(ClassPool.java:896)
  | 	at javassist.ClassPool.toClass(ClassPool.java:854)
  | 	at javassist.CtClass.toClass(CtClass.java:1053)
  | 	at com.blabla.test.PlainTester.testMethodInjection(PlainTester.java:32)
  | 
  | Caused by: java.lang.LinkageError: duplicate class definition: com/blabla/test/Hello
  | 	at java.lang.ClassLoader.defineClass1(Native Method)
  | 	at java.lang.ClassLoader.defineClass(ClassLoader.java:620)
  | 	at java.lang.ClassLoader.defineClass(ClassLoader.java:465)
  | 	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  | 	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
  | 	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
  | 	at java.lang.reflect.Method.invoke(Method.java:585)
  | 	at javassist.ClassPool.toClass2(ClassPool.java:965)
  | 	at javassist.ClassPool.toClass(ClassPool.java:947)
  | 	... 6 more

Of course, if I don't use the Hello class before injecting that method, it works fine. All the sample programs that I found on the net are showing a method injection without any prior use. However, my requirement is that, I have to be able to change a class while the system is running.

Is there any way that we can do that?

Your help is greatly appreciated...


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