Agent.java

/*
 * Copyright (c) 2013, 2014, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */
import java.security.*;
import java.lang.instrument.*;
import java.lang.reflect.*;

public class Agent implements ClassFileTransformer {
    public synchronized byte[] transform(final ClassLoader classLoader,
                                         final String className,
                                         Class<?> classBeingRedefined,
                                         ProtectionDomain protectionDomain,
                                         byte[] classfileBuffer) {
        System.out.println("Transforming class " + className);
        return classfileBuffer;
    }

    public static void redefine(String agentArgs, Instrumentation instrumentation, Class to_redefine) {

        try {
            instrumentation.retransformClasses(to_redefine);
        } catch (Exception e) {
            e.printStackTrace();
        }

    }

    public static void premain(String agentArgs, Instrumentation instrumentation) {
        Agent transformer = new Agent();
        instrumentation.addTransformer(transformer, true);

        // Redefine java/lang/Object and java/lang/reflect/Method.invoke and
        // java/lang/ClassLoader
        Class object_class = Object.class;
        redefine(agentArgs, instrumentation, object_class);

        Class method_class = Method.class;
        redefine(agentArgs, instrumentation, method_class);

        Class loader_class = ClassLoader.class;
        redefine(agentArgs, instrumentation, loader_class);

        instrumentation.removeTransformer(transformer);
    }

    public static void main(String[] args) {
        byte[] ba = new byte[0];

        // If it survives 100 GC's, it's good.
        for (int i = 0; i < 100 ; i++) {
            System.gc();
            ba.clone();
        }
        try {
            // Use java/lang/reflect/Method.invoke to call
            WalkThroughInvoke a = new WalkThroughInvoke();
            Class aclass = WalkThroughInvoke.class;
            Method m = aclass.getMethod("stackWalk");
            m.invoke(a);
        } catch (Exception x) {
            x.printStackTrace();
        }
    }
}