1 /*
   2  * Copyright (c) 2015, 2019, 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       try (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     /**
  64      * @return the number of occurrences of the <code>from</code> string that
  65      * have been replaced.
  66      */
  67     public static int replace(byte buff[], String from, String to) {
  68         if (to.length() != from.length()) {
  69             throw new RuntimeException("bad strings");
  70         }
  71         byte f[] = asciibytes(from);
  72         byte t[] = asciibytes(to);
  73         byte f0 = f[0];
  74 
  75         int numReplaced = 0;
  76         int max = buff.length - f.length;
  77         for (int i=0; i<max; ) {
  78             if (buff[i] == f0 && replace(buff, f, t, i)) {
  79                 i += f.length;
  80                 numReplaced ++;
  81             } else {
  82                 i++;
  83             }
  84         }
  85         return numReplaced;
  86     }
  87 
  88     public static boolean replace(byte buff[], byte f[], byte t[], int i) {
  89         for (int x=0; x<f.length; x++) {
  90             if (buff[x+i] != f[x]) {
  91                 return false;
  92             }
  93         }
  94         for (int x=0; x<f.length; x++) {
  95             buff[x+i] = t[x];
  96         }
  97         return true;
  98     }
  99 
 100     static byte[] asciibytes(String s) {
 101         byte b[] = new byte[s.length()];
 102         for (int i=0; i<b.length; i++) {
 103             b[i] = (byte)s.charAt(i);
 104         }
 105         return b;
 106     }
 107 
 108     public static Class defineClassFromJAR(ClassLoader loader, File jarFile, String className)
 109         throws FileNotFoundException, IOException, NoSuchMethodException, IllegalAccessException,
 110                InvocationTargetException {
 111         return defineClassFromJAR(loader, jarFile, className, null, null);
 112     }
 113 
 114     /**
 115      * Invoke the loader.defineClass() class method to define the named class stored in a JAR file.
 116      *
 117      * If a class exists both in the classpath, as well as in the list of URLs of a URLClassLoader,
 118      * by default, the URLClassLoader will not define the class, and instead will delegate to the
 119      * app loader. This method is an easy way to force the class to be defined by the URLClassLoader.
 120      *
 121      * Optionally, you can modify the contents of the classfile buffer. See comments in
 122      * defineModifiedClass.
 123      */
 124     public static Class defineClassFromJAR(ClassLoader loader, File jarFile, String className,
 125                                            String fromString, String toString)
 126         throws FileNotFoundException, IOException, NoSuchMethodException, IllegalAccessException,
 127                InvocationTargetException
 128     {
 129         byte[] buff = getClassFileFromJar(jarFile, className);
 130 
 131         if (fromString != null) {
 132             replace(buff, fromString, toString);
 133         }
 134 
 135         //System.out.println("Loading from: " + ent + " (" + buff.length + " bytes)");
 136 
 137         Method defineClass = ClassLoader.class.getDeclaredMethod("defineClass",
 138                                                                  buff.getClass(), int.class, int.class);
 139         defineClass.setAccessible(true);
 140         Class cls = (Class)defineClass.invoke(loader, buff, new Integer(0), new Integer(buff.length));
 141 
 142         //System.out.println("Loaded : " + cls);
 143         return cls;
 144     }
 145 
 146     public static byte[] getClassFileFromJar(File jarFile, String className) throws FileNotFoundException, IOException {
 147         JarFile jf = new JarFile(jarFile);
 148         JarEntry ent = jf.getJarEntry(className.replace('.', '/') + ".class");
 149 
 150         try (DataInputStream dis = new DataInputStream(jf.getInputStream(ent))) {
 151             byte[] buff = new byte[(int)ent.getSize()];
 152             dis.readFully(buff);
 153             return buff;
 154         }
 155     }
 156 }