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Javassist (JAVA programming ASSISTant) makes Java bytecode manipulation
simple. It is a class library for editing bytecodes in Java.
/*
* Javassist, a Java-bytecode translator toolkit.
* Copyright (C) 1999- Shigeru Chiba. All Rights Reserved.
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (the "License"); you may not use this file except in compliance with
* the License. Alternatively, the contents of this file may be used under
* the terms of the GNU Lesser General Public License Version 2.1 or later,
* or the Apache License Version 2.0.
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
* for the specific language governing rights and limitations under the
* License.
*/
package javassist.bytecode;
import java.io.PrintStream;
import javassist.CtMethod;
/**
* Simple utility class for printing the bytecode instructions of a method.
*
* @author Jason T. Greene
*/
public class InstructionPrinter implements Opcode {
private final static String opcodes[] = Mnemonic.OPCODE;
private final PrintStream stream;
/**
* Constructs a InstructionPrinter object.
*/
public InstructionPrinter(PrintStream stream) {
this.stream = stream;
}
/**
* Prints the bytecode instructions of a given method.
*/
public static void print(CtMethod method, PrintStream stream) {
(new InstructionPrinter(stream)).print(method);
}
/**
* Prints the bytecode instructions of a given method.
*/
public void print(CtMethod method) {
MethodInfo info = method.getMethodInfo2();
ConstPool pool = info.getConstPool();
CodeAttribute code = info.getCodeAttribute();
if (code == null)
return;
CodeIterator iterator = code.iterator();
while (iterator.hasNext()) {
int pos;
try {
pos = iterator.next();
} catch (BadBytecode e) {
throw new RuntimeException(e);
}
stream.println(pos + ": " + instructionString(iterator, pos, pool));
}
}
/**
* Gets a string representation of the bytecode instruction at the specified
* position.
*/
public static String instructionString(CodeIterator iter, int pos, ConstPool pool) {
int opcode = iter.byteAt(pos);
if (opcode > opcodes.length || opcode < 0)
throw new IllegalArgumentException("Invalid opcode, opcode: " + opcode + " pos: "+ pos);
String opstring = opcodes[opcode];
switch (opcode) {
case BIPUSH:
return opstring + " " + iter.byteAt(pos + 1);
case SIPUSH:
return opstring + " " + iter.s16bitAt(pos + 1);
case LDC:
return opstring + " " + ldc(pool, iter.byteAt(pos + 1));
case LDC_W :
case LDC2_W :
return opstring + " " + ldc(pool, iter.u16bitAt(pos + 1));
case ILOAD:
case LLOAD:
case FLOAD:
case DLOAD:
case ALOAD:
case ISTORE:
case LSTORE:
case FSTORE:
case DSTORE:
case ASTORE:
return opstring + " " + iter.byteAt(pos + 1);
case IFEQ:
case IFGE:
case IFGT:
case IFLE:
case IFLT:
case IFNE:
case IFNONNULL:
case IFNULL:
case IF_ACMPEQ:
case IF_ACMPNE:
case IF_ICMPEQ:
case IF_ICMPGE:
case IF_ICMPGT:
case IF_ICMPLE:
case IF_ICMPLT:
case IF_ICMPNE:
return opstring + " " + (iter.s16bitAt(pos + 1) + pos);
case IINC:
return opstring + " " + iter.byteAt(pos + 1) + ", " + iter.signedByteAt(pos + 2);
case GOTO:
case JSR:
return opstring + " " + (iter.s16bitAt(pos + 1) + pos);
case RET:
return opstring + " " + iter.byteAt(pos + 1);
case TABLESWITCH:
return tableSwitch(iter, pos);
case LOOKUPSWITCH:
return lookupSwitch(iter, pos);
case GETSTATIC:
case PUTSTATIC:
case GETFIELD:
case PUTFIELD:
return opstring + " " + fieldInfo(pool, iter.u16bitAt(pos + 1));
case INVOKEVIRTUAL:
case INVOKESPECIAL:
case INVOKESTATIC:
return opstring + " " + methodInfo(pool, iter.u16bitAt(pos + 1));
case INVOKEINTERFACE:
return opstring + " " + interfaceMethodInfo(pool, iter.u16bitAt(pos + 1));
case INVOKEDYNAMIC:
return opstring + " " + iter.u16bitAt(pos + 1);
case NEW:
return opstring + " " + classInfo(pool, iter.u16bitAt(pos + 1));
case NEWARRAY:
return opstring + " " + arrayInfo(iter.byteAt(pos + 1));
case ANEWARRAY:
case CHECKCAST:
return opstring + " " + classInfo(pool, iter.u16bitAt(pos + 1));
case WIDE:
return wide(iter, pos);
case MULTIANEWARRAY:
return opstring + " " + classInfo(pool, iter.u16bitAt(pos + 1));
case GOTO_W:
case JSR_W:
return opstring + " " + (iter.s32bitAt(pos + 1)+ pos);
default:
return opstring;
}
}
private static String wide(CodeIterator iter, int pos) {
int opcode = iter.byteAt(pos + 1);
int index = iter.u16bitAt(pos + 2);
switch (opcode) {
case ILOAD:
case LLOAD:
case FLOAD:
case DLOAD:
case ALOAD:
case ISTORE:
case LSTORE:
case FSTORE:
case DSTORE:
case ASTORE:
case IINC:
case RET:
return opcodes[opcode] + " " + index;
default:
throw new RuntimeException("Invalid WIDE operand");
}
}
private static String arrayInfo(int type) {
switch (type) {
case T_BOOLEAN:
return "boolean";
case T_CHAR:
return "char";
case T_BYTE:
return "byte";
case T_SHORT:
return "short";
case T_INT:
return "int";
case T_LONG:
return "long";
case T_FLOAT:
return "float";
case T_DOUBLE:
return "double";
default:
throw new RuntimeException("Invalid array type");
}
}
private static String classInfo(ConstPool pool, int index) {
return "#" + index + " = Class " + pool.getClassInfo(index);
}
private static String interfaceMethodInfo(ConstPool pool, int index) {
return "#" + index + " = Method "
+ pool.getInterfaceMethodrefClassName(index) + "."
+ pool.getInterfaceMethodrefName(index) + "("
+ pool.getInterfaceMethodrefType(index) + ")";
}
private static String methodInfo(ConstPool pool, int index) {
return "#" + index + " = Method "
+ pool.getMethodrefClassName(index) + "."
+ pool.getMethodrefName(index) + "("
+ pool.getMethodrefType(index) + ")";
}
private static String fieldInfo(ConstPool pool, int index) {
return "#" + index + " = Field "
+ pool.getFieldrefClassName(index) + "."
+ pool.getFieldrefName(index) + "("
+ pool.getFieldrefType(index) + ")";
}
private static String lookupSwitch(CodeIterator iter, int pos) {
StringBuffer buffer = new StringBuffer("lookupswitch {\n");
int index = (pos & ~3) + 4;
// default
buffer.append("\t\tdefault: ").append(pos + iter.s32bitAt(index)).append("\n");
int npairs = iter.s32bitAt(index += 4);
int end = npairs * 8 + (index += 4);
for (; index < end; index += 8) {
int match = iter.s32bitAt(index);
int target = iter.s32bitAt(index + 4) + pos;
buffer.append("\t\t").append(match).append(": ").append(target).append("\n");
}
buffer.setCharAt(buffer.length() - 1, '}');
return buffer.toString();
}
private static String tableSwitch(CodeIterator iter, int pos) {
StringBuffer buffer = new StringBuffer("tableswitch {\n");
int index = (pos & ~3) + 4;
// default
buffer.append("\t\tdefault: ").append(pos + iter.s32bitAt(index)).append("\n");
int low = iter.s32bitAt(index += 4);
int high = iter.s32bitAt(index += 4);
int end = (high - low + 1) * 4 + (index += 4);
// Offset table
for (int key = low; index < end; index += 4, key++) {
int target = iter.s32bitAt(index) + pos;
buffer.append("\t\t").append(key).append(": ").append(target).append("\n");
}
buffer.setCharAt(buffer.length() - 1, '}');
return buffer.toString();
}
private static String ldc(ConstPool pool, int index) {
int tag = pool.getTag(index);
switch (tag) {
case ConstPool.CONST_String:
return "#" + index + " = \"" + pool.getStringInfo(index) + "\"";
case ConstPool.CONST_Integer:
return "#" + index + " = int " + pool.getIntegerInfo(index);
case ConstPool.CONST_Float:
return "#" + index + " = float " + pool.getFloatInfo(index);
case ConstPool.CONST_Long:
return "#" + index + " = long " + pool.getLongInfo(index);
case ConstPool.CONST_Double:
return "#" + index + " = int " + pool.getDoubleInfo(index);
case ConstPool.CONST_Class:
return classInfo(pool, index);
default:
throw new RuntimeException("bad LDC: " + tag);
}
}
}