ClassLoaderPatcher.java

/**************************************************************************************
 * Copyright (c) Jonas Bon�r, Alexandre Vasseur. All rights reserved.                 *
 * http://aspectwerkz.codehaus.org                                                    *
 * ---------------------------------------------------------------------------------- *
 * The software in this package is published under the terms of the LGPL license      *
 * a copy of which has been included with this distribution in the license.txt file.  *
 **************************************************************************************/
package org.codehaus.aspectwerkz.hook;

import java.io.BufferedOutputStream;
import java.io.ByteArrayOutputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;

/**
 * Utility methods to manipulate class redefinition of java.lang.ClassLoader in xxxStarter
 *
 * @author <a href="mailto:alex@gnilux.com">Alexandre Vasseur </a>
 */
public class ClassLoaderPatcher {
    /**
     * Converts an input stream to a byte[]
     */
    public static byte[] inputStreamToByteArray(InputStream is) throws IOException {
        ByteArrayOutputStream os = new ByteArrayOutputStream();
        for (int b = is.read(); b != -1; b = is.read()) {
            os.write(b);
        }
        return os.toByteArray();
    }

    /**
     * Gets the bytecode of the modified java.lang.ClassLoader using given ClassLoaderPreProcessor class name
     */
    static byte[] getPatchedClassLoader(String preProcessorName) {
        byte[] abyte = null;
        InputStream is = null;
        try {
            is = ClassLoader.getSystemClassLoader().getParent().getResourceAsStream("java/lang/ClassLoader.class");
            abyte = inputStreamToByteArray(is);
        } catch (IOException e) {
            throw new Error("failed to read java.lang.ClassLoader: " + e.toString());
        } finally {
            try {
                is.close();
            } catch (Exception e) {
                ;
            }
        }
        if (preProcessorName != null) {
            try {
                ClassLoaderPreProcessor clpi = (ClassLoaderPreProcessor) Class.forName(preProcessorName).newInstance();
                abyte = clpi.preProcess(abyte);
            } catch (Exception e) {
                System.err.println("failed to instrument java.lang.ClassLoader: preprocessor not found");
                e.printStackTrace();
            }
        }
        return abyte;
    }

    /**
     * Dump bytecode bytes in dir/className.class directory, created if needed
     */
    private static void writeClass(String className, byte[] bytes, String dir) {
        String filename = dir + File.separatorChar + className.replace('.', File.separatorChar) + ".class";
        int pos = filename.lastIndexOf(File.separatorChar);
        if (pos > 0) {
            String finalDir = filename.substring(0, pos);
            (new File(finalDir)).mkdirs();
        }
        try {
            DataOutputStream out = new DataOutputStream(new BufferedOutputStream(new FileOutputStream(filename)));
            out.write(bytes);
            out.close();
        } catch (IOException e) {
            System.err.println("failed to write " + className + " in " + dir);
            e.printStackTrace();
        }
    }

    /**
     * Patch java.lang.ClassLoader with preProcessorName instance and dump class bytecode in dir
     */
    public static void patchClassLoader(String preProcessorName, String dir) {
        byte[] cl = getPatchedClassLoader(preProcessorName);
        writeClass("java.lang.ClassLoader", cl, dir);
    }

}