1 /*
2  * Copyright (c) 2014, 2018, 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 package gc.g1.unloading.bytecode;
24 
25 import java.util.*;
26 
27 
28 /**
29  * This utility class replaces peaces of bytes in bytecode by another peaces according to dictionary. This is useful for class redefenition.
30  */
31 public class BytecodePatcher {
32 
33     static private Map<byte[], byte[]> dictionary = new HashMap<>();
34 
35     static {
36         dictionary.put("bytesToReplace0".getBytes(), "bytesToReplace1".getBytes());
37         dictionary.put("bytesToReplace2".getBytes(), "bytesToReplace3".getBytes());
38     }
39 
patch(byte[] bytecode)40     public static void patch(byte[] bytecode) {
41         for (Map.Entry<byte[], byte[]> entry : dictionary.entrySet()) {
42             for (int i = 0; i + entry.getKey().length < bytecode.length; i++) {
43                 boolean match = true;
44                 for (int j = 0; j < entry.getKey().length; j++) {
45                     if (bytecode[i + j] != entry.getKey()[j]) {
46                         match = false;
47                         break;
48                     }
49                 }
50                 if (match) {
51                     for (int j = 0; j < entry.getKey().length; j++)
52                         bytecode[i + j] = entry.getValue()[j];
53                 }
54             }
55         }
56     }
57 
58 }
59