Agent.java revision 5776:de6a9e811145 
1/*
2 * Copyright (c) 2013, 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 */
23import java.security.*;
24import java.lang.instrument.*;
25import java.lang.reflect.*;
26
27public 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 1000 GC's, it's good.
69        for (int i = 0; i < 1000 ; 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}
84