在深入分析ClassReader.readCode()方法之前，我们需要大概了解下ASM把jvm的指令分的类型，这在readCode会用到。先看ClassReader的代码：
static {
int i;
byte[] b = new byte[220];
String s = "AAAAAAAAAAAAAAAABCLMMDDDDDEEEEEEEEEEEEEEEEEEEEAAAAAAAADD"
+ "DDDEEEEEEEEEEEEEEEEEEEEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
+ "AAAAAAAAAAAAAAAAANAAAAAAAAAAAAAAAAAAAAJJJJJJJJJJJJJJJJDOPAA"
+ "AAAAGGGGGGGHIFBFAAFFAARQJJKKJJJJJJJJJJJJJJJJJJ";
for (i = 0; i < b.length; ++i) {
b[i] = (byte) (s.charAt(i) - 'A');
}
TYPE = b;
}
这其中的TYPE是一个字节数组，索引是jvm指令的byte值，值从0开始，分了16类，简化后是：
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 2,11,12, 12,3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 0, 0, 0, 0, 0, 0, 0, 0, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,13, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 3, 14,15,0, 0, 0, 0, 0, 0, 6, 6, 6, 6, 6, 6, 6, 7, 8, 5, 1, 5, 0, 0, 5, 5, 0, 0, 17,16,9, 9, 10,10, 9, 9, 9, 9, 9,9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9
补全下，指令跟指令类型的对照表：
指令操作码 16进制 指令类型 指令 ##类型为0的指令没有操作数 0 = 0x0 = 0 ...............nop 1 = 0x1 = 0 ...............aconst_null 2 = 0x2 = 0 ...............iconst_m1 3 = 0x3 = 0 ...............iconst_0 4 = 0x4 = 0 ...............iconst_1 5 = 0x5 = 0 ...............iconst_2 6 = 0x6 = 0 ...............iconst_3 7 = 0x7 = 0 ...............iconst_4 8 = 0x8 = 0 ...............iconst_5 9 = 0x9 = 0 ...............lconst_0 10 = 0xa = 0 ...............lconst_1 11 = 0xb = 0 ...............fconst_0 12 = 0xc = 0 ...............fconst_1 13 = 0xd = 0 ...............fconst_2 14 = 0xe = 0 ...............dconst_0 15 = 0xf = 0 ...............dconst_1 ##类型为1的指令操作数长度为1个字节 16 = 0x10 = 1 ...............bipush ##类型为2的指令操作数长度为2个字节 17 = 0x11 = 2 ...............sipush 18 = 0x12 = 11 ...............ldc 19 = 0x13 = 12 ...............ldc_w 20 = 0x14 = 12 ...............ldc2_w ##类型为3的指令操作数长度为1个字节 21 = 0x15 = 3 ...............iload 22 = 0x16 = 3 ...............lload 23 = 0x17 = 3 ...............fload 24 = 0x18 = 3 ...............dload 25 = 0x19 = 3 ...............aload ##类型为4的指令操作数长度为1个字节 26 = 0x1a = 4 ...............iload_0 27 = 0x1b = 4 ...............iload_1 28 = 0x1c = 4 ...............iload_2 29 = 0x1d = 4 ...............iload_3 30 = 0x1e = 4 ...............lload_0 31 = 0x1f = 4 ...............lload_1 32 = 0x20 = 4 ...............lload_2 33 = 0x21 = 4 ...............lload_3 34 = 0x22 = 4 ...............fload_0 35 = 0x23 = 4 ...............fload_1 36 = 0x24 = 4 ...............fload_2 37 = 0x25 = 4 ...............fload_3 38 = 0x26 = 4 ...............dload_0 39 = 0x27 = 4 ...............dload_1 40 = 0x28 = 4 ...............dload_2 41 = 0x29 = 4 ...............dload_3 42 = 0x2a = 4 ...............aload_0 43 = 0x2b = 4 ...............aload_1 44 = 0x2c = 4 ...............aload_2 45 = 0x2d = 4 ...............aload_3 46 = 0x2e = 0 ...............iaload 47 = 0x2f = 0 ...............laload 48 = 0x30 = 0 ...............faload 49 = 0x31 = 0 ...............daload 50 = 0x32 = 0 ...............aaload 51 = 0x33 = 0 ...............baload 52 = 0x34 = 0 ...............caload 53 = 0x35 = 0 ...............saload 54 = 0x36 = 3 ...............istore 55 = 0x37 = 3 ...............lstore 56 = 0x38 = 3 ...............fstore 57 = 0x39 = 3 ...............dstore 58 = 0x3a = 3 ...............astore 59 = 0x3b = 4 ...............istore_0 60 = 0x3c = 4 ...............istore_1 61 = 0x3d = 4 ...............istore_2 62 = 0x3e = 4 ...............istore_3 63 = 0x3f = 4 ...............lstore_0 64 = 0x40 = 4 ...............lstore_1 65 = 0x41 = 4 ...............lstore_2 66 = 0x42 = 4 ...............lstore_3 67 = 0x43 = 4 ...............fstore_0 68 = 0x44 = 4 ...............fstore_1 69 = 0x45 = 4 ...............fstore_2 70 = 0x46 = 4 ...............fstore_3 71 = 0x47 = 4 ...............dstore_0 72 = 0x48 = 4 ...............dstore_1 73 = 0x49 = 4 ...............dstore_2 74 = 0x4a = 4 ...............dstore_3 75 = 0x4b = 4 ...............astore_0 76 = 0x4c = 4 ...............astore_1 77 = 0x4d = 4 ...............astore_2 78 = 0x4e = 4 ...............astore_3 79 = 0x4f = 0 ...............iastore 80 = 0x50 = 0 ...............lastore 81 = 0x51 = 0 ...............fastore 82 = 0x52 = 0 ...............dastore 83 = 0x53 = 0 ...............aastore 84 = 0x54 = 0 ...............bastore 85 = 0x55 = 0 ...............castore 86 = 0x56 = 0 ...............sastore 87 = 0x57 = 0 ...............pop 88 = 0x58 = 0 ...............pop2 89 = 0x59 = 0 ...............dup 90 = 0x5a = 0 ...............dup_x1 91 = 0x5b = 0 ...............dup_x2 92 = 0x5c = 0 ...............dup2 93 = 0x5d = 0 ...............dup2_x1 94 = 0x5e = 0 ...............dup2_x2 95 = 0x5f = 0 ...............swap 96 = 0x60 = 0 ...............iadd 97 = 0x61 = 0 ...............ladd 98 = 0x62 = 0 ...............fadd 99 = 0x63 = 0 ...............dadd 100 = 0x64 = 0 ...............isub 101 = 0x65 = 0 ...............lsub 102 = 0x66 = 0 ...............fsub 103 = 0x67 = 0 ...............dsub 104 = 0x68 = 0 ...............imul 105 = 0x69 = 0 ...............lmul 106 = 0x6a = 0 ...............fmul 107 = 0x6b = 0 ...............dmul 108 = 0x6c = 0 ...............idiv 109 = 0x6d = 0 ...............ldiv 110 = 0x6e = 0 ...............fdiv 111 = 0x6f = 0 ...............ddiv 112 = 0x70 = 0 ...............irem 113 = 0x71 = 0 ...............lrem 114 = 0x72 = 0 ...............frem 115 = 0x73 = 0 ...............drem 116 = 0x74 = 0 ...............ineg 117 = 0x75 = 0 ...............lneg 118 = 0x76 = 0 ...............fneg 119 = 0x77 = 0 ...............dneg 120 = 0x78 = 0 ...............ishl 121 = 0x79 = 0 ...............lshl 122 = 0x7a = 0 ...............ishr 123 = 0x7b = 0 ...............lshr 124 = 0x7c = 0 ...............iushr 125 = 0x7d = 0 ...............lushr 126 = 0x7e = 0 ...............iand 127 = 0x7f = 0 ...............land 128 = 0x80 = 0 ...............ior 129 = 0x81 = 0 ...............lor 130 = 0x82 = 0 ...............ixor 131 = 0x83 = 0 ...............lxor 132 = 0x84 = 13 ...............iinc 133 = 0x85 = 0 ...............i2l 134 = 0x86 = 0 ...............i2f 135 = 0x87 = 0 ...............i2d 136 = 0x88 = 0 ...............l2i 137 = 0x89 = 0 ...............l2f 138 = 0x8a = 0 ...............l2d 139 = 0x8b = 0 ...............f2i 140 = 0x8c = 0 ...............f2l 141 = 0x8d = 0 ...............f2d 142 = 0x8e = 0 ...............d2i 143 = 0x8f = 0 ...............d2l 144 = 0x90 = 0 ...............d2f 145 = 0x91 = 0 ...............i2b 146 = 0x92 = 0 ...............i2c 147 = 0x93 = 0 ...............i2s 148 = 0x94 = 0 ...............lcmp 149 = 0x95 = 0 ...............fcmpl 150 = 0x96 = 0 ...............fcmpg 151 = 0x97 = 0 ...............dcmpl 152 = 0x98 = 0 ...............dcmpg #类型为9的指令，主要是if、goto、jsr三大类指令 153 = 0x99 = 9 ...............ifeq 154 = 0x9a = 9 ...............ifne 155 = 0x9b = 9 ...............iflt 156 = 0x9c = 9 ...............ifge 157 = 0x9d = 9 ...............ifgt 158 = 0x9e = 9 ...............ifle 159 = 0x9f = 9 ...............if_icmpeq 160 = 0xa0 = 9 ...............if_icmpne 161 = 0xa1 = 9 ...............if_icmplt 162 = 0xa2 = 9 ...............if_icmpge 163 = 0xa3 = 9 ...............if_icmpgt 164 = 0xa4 = 9 ...............if_icmple 165 = 0xa5 = 9 ...............if_acmpeq 166 = 0xa6 = 9 ...............if_acmpne 167 = 0xa7 = 9 ...............goto 168 = 0xa8 = 9 ...............jsr 169 = 0xa9 = 3 ...............ret #14 tableswitch 对齐变长，high(4) / low(4) / offsets[(high-low+1)*4] 170 = 0xaa = 14 ...............tableswitch #15 lookupswitch 对齐变长 default(4) / npairs(4) / match(4) - offset(4) pairs 171 = 0xab = 15 ...............lookupswitch 172 = 0xac = 0 ...............ireturn 173 = 0xad = 0 ...............lreturn 174 = 0xae = 0 ...............freturn 175 = 0xaf = 0 ...............dreturn 176 = 0xb0 = 0 ...............areturn 177 = 0xb1 = 0 ...............return 178 = 0xb2 = 6 ...............getstatic 179 = 0xb3 = 6 ...............putstatic 180 = 0xb4 = 6 ...............getfield 181 = 0xb5 = 6 ...............putfield 182 = 0xb6 = 6 ...............invokevirtual 183 = 0xb7 = 6 ...............invokespecial 184 = 0xb8 = 6 ...............invokestatic 185 = 0xb9 = 7 ...............invokeinterface 186 = 0xba = 8 ...............invokedynamic 187 = 0xbb = 5 ...............new 188 = 0xbc = 1 ...............newarray 189 = 0xbd = 5 ...............anewarray 190 = 0xbe = 0 ...............arraylength 191 = 0xbf = 0 ...............athrow 192 = 0xc0 = 5 ...............checkcast 193 = 0xc1 = 5 ...............instanceof 194 = 0xc2 = 0 ...............monitorenter 195 = 0xc3 = 0 ...............monitorexit 196 = 0xc4 = 17 ...............wide 197 = 0xc5 = 16 ...............multianewarray 198 = 0xc6 = 9 ...............ifnull 199 = 0xc7 = 9 ...............ifnonnull #goto、jsr扩展指令 200 = 0xc8 = 10 ...............goto_w 201 = 0xc9 = 10 ...............jsr_w 202 = 0xca = 9 Reserved opcodes: 203 = 0xcb = 9 ...............breakpoint 204 = 0xcc = 9 ...............impdep1 205 = 0xcd = 9 ...............impdep2 206 = 0xce = 9 207 = 0xcf = 9 208 = 0xd0 = 9 209 = 0xd1 = 9 210 = 0xd2 = 9 211 = 0xd3 = 9 212 = 0xd4 = 9 213 = 0xd5 = 9 214 = 0xd6 = 9 215 = 0xd7 = 9 216 = 0xd8 = 9 217 = 0xd9 = 9 218 = 0xda = 9 219 = 0xdb = 9