1 /*
   2  * Copyright (c) 2013, 2014, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  */
  23 import java.security.*;
  24 import java.lang.instrument.*;
  25 import java.lang.reflect.*;
  26 
  27 public class Agent implements ClassFileTransformer {
  28     public synchronized byte[] transform(final ClassLoader classLoader,
  29                                          final String className,
  30                                          Class<?> classBeingRedefined,
  31                                          ProtectionDomain protectionDomain,
  32                                          byte[] classfileBuffer) {
  33         System.out.println("Transforming class " + className);
  34         return classfileBuffer;
  35     }
  36 
  37     public static void redefine(String agentArgs, Instrumentation instrumentation, Class to_redefine) {
  38 
  39         try {
  40             instrumentation.retransformClasses(to_redefine);
  41         } catch (Exception e) {
  42             e.printStackTrace();
  43         }
  44 
  45     }
  46 
  47     public static void premain(String agentArgs, Instrumentation instrumentation) {
  48         Agent transformer = new Agent();
  49         instrumentation.addTransformer(transformer, true);
  50 
  51         // Redefine java/lang/Object and java/lang/reflect/Method.invoke and
  52         // java/lang/ClassLoader
  53         Class object_class = Object.class;
  54         redefine(agentArgs, instrumentation, object_class);
  55 
  56         Class method_class = Method.class;
  57         redefine(agentArgs, instrumentation, method_class);
  58 
  59         Class loader_class = ClassLoader.class;
  60         redefine(agentArgs, instrumentation, loader_class);
  61 
  62         instrumentation.removeTransformer(transformer);
  63     }
  64 
  65     public static void main(String[] args) {
  66         byte[] ba = new byte[0];
  67 
  68         // If it survives 100 GC's, it's good.
  69         for (int i = 0; i < 100 ; i++) {
  70             System.gc();
  71             ba.clone();
  72         }
  73         try {
  74             // Use java/lang/reflect/Method.invoke to call
  75             WalkThroughInvoke a = new WalkThroughInvoke();
  76             Class aclass = WalkThroughInvoke.class;
  77             Method m = aclass.getMethod("stackWalk");
  78             m.invoke(a);
  79         } catch (Exception x) {
  80             x.printStackTrace();
  81         }
  82     }
  83 }