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.invoke.MethodHandles;
  27 import java.lang.invoke.MethodHandles.Lookup;
  28 import static java.lang.invoke.MethodHandles.*;
  29 import java.lang.reflect.*;
  30 import java.util.jar.*;
  31 
  32 public class Util {
  33     /**
  34      * Invoke the lookup.defineClass() class method to define the class stored in clsFile,
  35      * with the following modification:
  36      * <ul>
  37      *  <li> All ASCII strings in the class file bytes that matches fromString will be replaced with toString.
  38      *       NOTE: the two strings must be the exact same length.
  39      * </ul>
  40      */
  41     public static Class<?> defineModifiedClass(ClassLoader loader, File clsFile, String fromString, String toString)
  42         throws FileNotFoundException, IOException, NoSuchMethodException, IllegalAccessException,
  43                InvocationTargetException, ClassNotFoundException
  44     {
  45       try (DataInputStream dis = new DataInputStream(new FileInputStream(clsFile))) {
  46         byte[] buff = new byte[(int)clsFile.length()];
  47         dis.readFully(buff);
  48         replace(buff, fromString, toString);
  49 
  50         System.out.println("Loading from: " + clsFile + " (" + buff.length + " bytes)");
  51 
  52 
  53         // We directly call into Lookup.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<?> target = Class.forName("Hello", false, loader);
  57         Lookup lookup = privateLookupIn(target, lookup());
  58         Class<?> cls = lookup.defineClass(buff);
  59         System.out.println("Loaded : " + cls);
  60 
  61         return cls;
  62       }
  63     }
  64 
  65     /**
  66      * @return the number of occurrences of the <code>from</code> string that
  67      * have been replaced.
  68      */
  69     public static int replace(byte buff[], String from, String to) {
  70         if (to.length() != from.length()) {
  71             throw new RuntimeException("bad strings");
  72         }
  73         byte f[] = asciibytes(from);
  74         byte t[] = asciibytes(to);
  75         byte f0 = f[0];
  76 
  77         int numReplaced = 0;
  78         int max = buff.length - f.length;
  79         for (int i=0; i<max; ) {
  80             if (buff[i] == f0 && replace(buff, f, t, i)) {
  81                 i += f.length;
  82                 numReplaced ++;
  83             } else {
  84                 i++;
  85             }
  86         }
  87         return numReplaced;
  88     }
  89 
  90     public static boolean replace(byte buff[], byte f[], byte t[], int i) {
  91         for (int x=0; x<f.length; x++) {
  92             if (buff[x+i] != f[x]) {
  93                 return false;
  94             }
  95         }
  96         for (int x=0; x<f.length; x++) {
  97             buff[x+i] = t[x];
  98         }
  99         return true;
 100     }
 101 
 102     static byte[] asciibytes(String s) {
 103         byte b[] = new byte[s.length()];
 104         for (int i=0; i<b.length; i++) {
 105             b[i] = (byte)s.charAt(i);
 106         }
 107         return b;
 108     }
 109 
 110     public static Class defineClassFromJAR(ClassLoader loader, File jarFile, String className)
 111         throws FileNotFoundException, IOException, NoSuchMethodException, IllegalAccessException,
 112                InvocationTargetException, ClassNotFoundException {
 113         return defineClassFromJAR(loader, jarFile, className, null, null);
 114     }
 115 
 116     /**
 117      * Invoke the lookup.defineClass() class method to define the named class stored in a JAR file.
 118      *
 119      * If a class exists both in the classpath, as well as in the list of URLs of a URLClassLoader,
 120      * by default, the URLClassLoader will not define the class, and instead will delegate to the
 121      * app loader. This method is an easy way to force the class to be defined by the URLClassLoader.
 122      *
 123      * Optionally, you can modify the contents of the classfile buffer. See comments in
 124      * defineModifiedClass.
 125      */
 126     public static Class<?> defineClassFromJAR(ClassLoader loader, File jarFile, String className,
 127                                            String fromString, String toString)
 128         throws FileNotFoundException, IOException, NoSuchMethodException, IllegalAccessException,
 129                InvocationTargetException, ClassNotFoundException
 130     {
 131         byte[] buff = getClassFileFromJar(jarFile, className);
 132 
 133         if (fromString != null) {
 134             replace(buff, fromString, toString);
 135         }
 136 
 137         //System.out.println("Loading from: " + ent + " (" + buff.length + " bytes)");
 138 
 139         Class<?> target = Class.forName("Hello", false, loader);
 140         Lookup lookup = privateLookupIn(target, lookup());
 141         Class<?> cls = lookup.defineClass(buff);
 142 
 143         //System.out.println("Loaded : " + cls);
 144         return cls;
 145     }
 146 
 147     public static byte[] getClassFileFromJar(File jarFile, String className) throws FileNotFoundException, IOException {
 148         JarFile jf = new JarFile(jarFile);
 149         JarEntry ent = jf.getJarEntry(className.replace('.', '/') + ".class");
 150 
 151         try (DataInputStream dis = new DataInputStream(jf.getInputStream(ent))) {
 152             byte[] buff = new byte[(int)ent.getSize()];
 153             dis.readFully(buff);
 154             return buff;
 155         }
 156     }
 157 
 158 }