1 /*
   2  * Copyright (c) 2015, 2017, 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  */
  24 
  25 import java.io.*;
  26 import java.lang.reflect.*;
  27 import java.util.jar.*;
  28 
  29 public class Util {
  30     /**
  31      * Invoke the loader.defineClass() class method to define the class stored in clsFile,
  32      * with the following modification:
  33      * <ul>
  34      *  <li> All ASCII strings in the class file bytes that matches fromString will be replaced with toString.
  35      *       NOTE: the two strings must be the exact same length.
  36      * </ul>
  37      */
  38     public static Class defineModifiedClass(ClassLoader loader, File clsFile, String fromString, String toString)
  39         throws FileNotFoundException, IOException, NoSuchMethodException, IllegalAccessException,
  40                InvocationTargetException
  41     {
  42         DataInputStream dis = new DataInputStream(new FileInputStream(clsFile));
  43         byte[] buff = new byte[(int)clsFile.length()];
  44         dis.readFully(buff);
  45         replace(buff, fromString, toString);
  46 
  47         System.out.println("Loading from: " + clsFile + " (" + buff.length + " bytes)");
  48 
  49         Method defineClass = ClassLoader.class.getDeclaredMethod("defineClass",
  50                                                                  buff.getClass(), int.class, int.class);
  51         defineClass.setAccessible(true);
  52 
  53         // We directly call into ClassLoader.defineClass() to define the "Super" class. Also,
  54         // rewrite its classfile so that it returns ___yyy___ instead of ___xxx___. Changing the
  55         // classfile will guarantee that this class will NOT be loaded from the CDS archive.
  56         Class cls = (Class)defineClass.invoke(loader, buff, new Integer(0), new Integer(buff.length));
  57         System.out.println("Loaded : " + cls);
  58 
  59         return cls;
  60     }

  61 
  62     /**
  63      * @return the number of occurrences of the <code>from</code> string that
  64      * have been replaced.
  65      */
  66     public static int replace(byte buff[], String from, String to) {
  67         if (to.length() != from.length()) {
  68             throw new RuntimeException("bad strings");
  69         }
  70         byte f[] = asciibytes(from);
  71         byte t[] = asciibytes(to);
  72         byte f0 = f[0];
  73 
  74         int numReplaced = 0;
  75         int max = buff.length - f.length;
  76         for (int i=0; i<max; ) {
  77             if (buff[i] == f0 && replace(buff, f, t, i)) {
  78                 i += f.length;
  79                 numReplaced ++;
  80             } else {
  81                 i++;
  82             }
  83         }
  84         return numReplaced;
  85     }
  86 
  87     public static boolean replace(byte buff[], byte f[], byte t[], int i) {
  88         for (int x=0; x<f.length; x++) {
  89             if (buff[x+i] != f[x]) {
  90                 return false;
  91             }
  92         }
  93         for (int x=0; x<f.length; x++) {
  94             buff[x+i] = t[x];
  95         }
  96         return true;
  97     }
  98 
  99     static byte[] asciibytes(String s) {
 100         byte b[] = new byte[s.length()];
 101         for (int i=0; i<b.length; i++) {
 102             b[i] = (byte)s.charAt(i);
 103         }
 104         return b;
 105     }
 106 
 107     public static Class defineClassFromJAR(ClassLoader loader, File jarFile, String className)
 108         throws FileNotFoundException, IOException, NoSuchMethodException, IllegalAccessException,
 109                InvocationTargetException {
 110         return defineClassFromJAR(loader, jarFile, className, null, null);
 111     }
 112 
 113     /**
 114      * Invoke the loader.defineClass() class method to define the named class stored in a JAR file.
 115      *
 116      * If a class exists both in the classpath, as well as in the list of URLs of a URLClassLoader,
 117      * by default, the URLClassLoader will not define the class, and instead will delegate to the
 118      * app loader. This method is an easy way to force the class to be defined by the URLClassLoader.
 119      *
 120      * Optionally, you can modify the contents of the classfile buffer. See comments in
 121      * defineModifiedClass.
 122      */
 123     public static Class defineClassFromJAR(ClassLoader loader, File jarFile, String className,
 124                                            String fromString, String toString)
 125         throws FileNotFoundException, IOException, NoSuchMethodException, IllegalAccessException,
 126                InvocationTargetException
 127     {
 128         byte[] buff = getClassFileFromJar(jarFile, className);
 129 
 130         if (fromString != null) {
 131             replace(buff, fromString, toString);
 132         }
 133 
 134         //System.out.println("Loading from: " + ent + " (" + buff.length + " bytes)");
 135 
 136         Method defineClass = ClassLoader.class.getDeclaredMethod("defineClass",
 137                                                                  buff.getClass(), int.class, int.class);
 138         defineClass.setAccessible(true);
 139         Class cls = (Class)defineClass.invoke(loader, buff, new Integer(0), new Integer(buff.length));
 140 
 141         //System.out.println("Loaded : " + cls);
 142         return cls;
 143     }
 144 
 145     public static byte[] getClassFileFromJar(File jarFile, String className) throws FileNotFoundException, IOException {
 146         JarFile jf = new JarFile(jarFile);
 147         JarEntry ent = jf.getJarEntry(className.replace('.', '/') + ".class");
 148 
 149         DataInputStream dis = new DataInputStream(jf.getInputStream(ent));
 150         byte[] buff = new byte[(int)ent.getSize()];
 151         dis.readFully(buff);
 152         dis.close();
 153 
 154         return buff;

 155     }
 156 }
--- EOF ---