Rodrigo Uchoa [https://community.jboss.org/people/rodrigo.uchoa] created the discussion "Is is possible to instrument java core classes? Classes loaded by the bootstrap classloader" To view the discussion, visit: https://community.jboss.org/message/722476#722476 -------------------------------------------------------------- Hello! I want to add an "insertBefore" on a method of a core JDK 5 class. For some reason it´s not working. Here's the code: ClassPool pool = ClassPool.getDefault(); CtClass ctClass = pool.get("com.sun.org.apache.xerces.internal.impl.xs.XSMessageFormatter"); CtMethod ctMethod = ctClass.getDeclaredMethods()[0]; ctMethod.insertBefore("System.out.println(\"WORKED\");"); ctClass.toClass(); The +com.sun.org.apache.xerces.internal.impl.xs.XSMessageFormatter+ comes bundled with the JDK, it's inside rt.jar. After the snippet above, I run some code that forces the XSMessageFormatter class to run, but my inserted code never runs. I can only get this to work on my own classes. This code is running as a simple standalone app. Any ideas? -------------------------------------------------------------- Reply to this message by going to Community [https://community.jboss.org/message/722476#722476] Start a new discussion in Javassist at Community [https://community.jboss.org/choose-container!input.jspa?contentType=1&...]