TransformerAgent.java

/*
 * Copyright (c) 2016, 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.
 *
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import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.IllegalClassFormatException;
import java.lang.instrument.Instrumentation;
import java.security.ProtectionDomain;
import java.util.HashMap;

// This is a test utility class used to transform
// specified classes via initial transformation (ClassFileLoadHook).
// Names of classes to be transformed are supplied as arguments,
// the phrase to be transformed is a hard-coded predefined
// fairly unique phrase.

public class TransformerAgent {
    private static String[] classesToTransform;


    private static void log(String msg) {
        System.out.println("TransformerAgent: " + msg);
    }


    // arguments are comma-separated list of classes to transform
    public static void premain(String agentArguments, Instrumentation instrumentation) {
        log("premain() is called, arguments = " + agentArguments);
        classesToTransform = agentArguments.split(",");
        instrumentation.addTransformer(new SimpleTransformer(), /*canRetransform=*/true);
    }


    public static void agentmain(String args, Instrumentation inst) throws Exception {
        log("agentmain() is called");
        premain(args, inst);
    }


    static class SimpleTransformer implements ClassFileTransformer {
       public byte[] transform(ClassLoader loader, String name, Class<?> classBeingRedefined,
                            ProtectionDomain pd, byte[] buffer) throws IllegalClassFormatException {

            log("SimpleTransformer called for: " + name + "@" + incrCounter(name));
            if (!shouldTransform(name))
                return null;

            log("transforming: class name = " + name);
            int nrOfReplacements = TransformUtil.replace(buffer, TransformUtil.BeforePattern,
                                                         TransformUtil.AfterPattern);
            log("replaced the string, nrOfReplacements = " + nrOfReplacements);
            return buffer;
        }

        // Check class name pattern, since test should only transform certain classes
        private static boolean shouldTransform(String name) {
            for (String match : classesToTransform) {
                if (name.matches(match)) {
                    log("shouldTransform: match-found, match = " + match);
                    return true;
                }
            }

            return false;
        }
    }


    static HashMap<String, Integer> counterMap = new HashMap<>();

    static Integer incrCounter(String className) {
        Integer i = counterMap.get(className);
        if (i == null) {
            i = new Integer(1);
        } else {
            i = new Integer(i.intValue() + 1);
        }
        counterMap.put(className, i);
        return i;
    }
}