1 <html> 2 <!-- 3 * ASM: a very small and fast Java bytecode manipulation framework 4 * Copyright (c) 2000-2005 INRIA, France Telecom 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 3. Neither the name of the copyright holders nor the names of its 16 * contributors may be used to endorse or promote products derived from 17 * this software without specific prior written permission. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" 20 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE 23 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 24 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 25 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 26 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 27 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 28 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF 29 * THE POSSIBILITY OF SUCH DAMAGE. 30 --> 31 <body> 32 33 <p> 34 Provides an ASM visitor that constructs a tree representation of the 35 classes it visits. This class adapter can be useful to implement "complex" 36 class manipulation operations, i.e., operations that would be very hard to 37 implement without using a tree representation (such as optimizing the number 38 of local variables used by a method). 39 </p> 40 41 <p> 42 However, this class adapter has a cost: it makes ASM bigger and slower. Indeed 43 it requires more than twenty new classes, and multiplies the time needed to 44 transform a class by almost two (it is almost two times faster to read, "modify" 45 and write a class with a ClassAdapter than with a ClassNode). This is why 46 this package is bundled in an optional <tt>asm-tree.jar</tt> library that 47 is separated from (but requires) the <tt>asm.jar</tt> library, which contains 48 the core ASM framework. This is also why <i><font color="red">it is recommended 49 not to use this class adapter when it is possible</font></i>. 50 </p> 51 52 <p> 53 The root class is the ClassNode, that can be created from existing bytecode. For example: 54 </p> 55 56 <pre> 57 ClassReader cr = new ClassReader(source); 58 ClassNode cn = new ClassNode(); 59 cr.accept(cn, true); 60 </pre> 61 62 <p> 63 Now content of ClassNode can be modified and then 64 serialized back into bytecode: 65 </p> 66 67 <pre> 68 ClassWriter cw = new ClassWriter(true); 69 cn.accept(cw); 70 </pre> 71 72 <p> 73 Using simple ClassAdapter it is possible to create MethodNode instances per-method. 74 In this example MethodNode is acting as a buffer that is flushed out at visitEnd() call: 75 </p> 76 77 <pre> 78 ClassReader cr = new ClassReader(source); 79 ClassWriter cw = new ClassWriter(); 80 ClassAdapter ca = new ClassAdapter(cw) { 81 public MethodVisitor visitMethod(int access, String name, 82 String desc, String signature, String[] exceptions) { 83 final MethodVisitor mv = super.visitMethod(access, name, desc, signature, exceptions); 84 MethodNode mn = new MethodNode(access, name, desc, signature, exceptions) { 85 public void visitEnd() { 86 // transform or analyze method code using tree API 87 accept(mv); 88 } 89 }; 90 } 91 }; 92 cr.accept(ca, true); 93 </pre> 94 95 <p> 96 Several strategies can be used to construct method code from scratch. The first 97 option is to create a MethodNode, and then create XXXInsnNode instances and 98 add them to the instructions list: 99 </p> 100 101 <pre> 102 MethodNode m = new MethodNode(...); 103 m.instructions.add(new VarInsnNode(ALOAD, 0)); 104 ... 105 </pre> 106 107 <p> 108 Alternatively, you can use the fact that MethodNode is a MethodVisitor, and use 109 that to create the XXXInsnNode and add them to the instructions list through 110 the standard MethodVisitor interface: 111 </p> 112 113 <pre> 114 MethodNode m = new MethodNode(...); 115 m.visitVarInsn(ALOAD, 0); 116 ... 117 </pre> 118 119 <p> 120 If you cannot generate all the instructions in sequential order, i.e. if you 121 need to save some pointer in the instruction list and then insert instructions 122 at that place after other instructions have been generated, you can use InsnList 123 methods insert() and insertBefore() to insert instructions at saved pointer. 124 </p> 125 126 <pre> 127 MethodNode m = new MethodNode(...); 128 m.visitVarInsn(ALOAD, 0); 129 AbstractInsnNode ptr = m.instructions.getLast(); 130 m.visitVarInsn(ALOAD, 1); 131 // inserts an instruction between ALOAD 0 and ALOAD 1 132 m.instructions.insert(ptr, new VarInsnNode(ALOAD, 0)); 133 ... 134 </pre> 135 136 <p> 137 If you need to insert instructions while iterating over an existing instruction 138 list, you can also use several strategies. The first one is to use a 139 ListIterator over the instruction list: 140 </p> 141 142 <pre> 143 ListIterator it = m.instructions.iterator(); 144 while (it.hasNext()) { 145 AbstractInsnNode n = (AbstractInsnNode) it.next(); 146 if (...) { 147 it.add(new VarInsnNode(ALOAD, 0)); 148 } 149 } 150 </pre> 151 152 <p> 153 It is also possible to convert instruction list into the array and iterate trough 154 array elements: 155 </p> 156 157 <pre> 158 AbstractInsnNode[] insns = m.instructions.toArray(); 159 for(int i = 0; i<insns.length; i++) { 160 AbstractInsnNode n = insns[i]; 161 if (...) { 162 m.instructions.insert(n, new VarInsnNode(ALOAD, 0)); 163 } 164 } 165 </pre> 166 167 <p> 168 If you want to insert these instructions through the MethodVisitor interface, 169 you can use another instance of MethodNode as a MethodVisitor and then 170 insert instructions collected by that instance into the instruction list. 171 For example: 172 </p> 173 174 <pre> 175 AbstractInsnNode[] insns = m.instructions.toArray(); 176 for(int i = 0; i<insns.length; i++) { 177 AbstractInsnNode n = insns[i]; 178 if (...) { 179 MethodNode mn = new MethodNode(); 180 mn.visitVarInsn(ALOAD, 0); 181 mn.visitVarInsn(ALOAD, 1); 182 m.instructions.insert(n, mn.instructions); 183 } 184 } 185 </pre> 186 187 <p> 188 @since ASM 1.3.3 189 </p> 190 191 </body> 192 </html> 193
