Java 使用ASM选择和修改'if'语句
我想在特定行上更新已有类中的Java 使用ASM选择和修改'if'语句,java,java-bytecode-asm,bytecode-manipulation,Java,Java Bytecode Asm,Bytecode Manipulation,我想在特定行上更新已有类中的if语句，而不改变整个方法 以下是目标代码（类、方法的名称和一些因不相关而更改的代码）： 在这段代码中，我想将if（firstPar.check（））更改为如下内容： if(firstPar.check() && !Utilities.someOtherCheck(firstPar, secondPar)) 以下是我试图解决这个问题的方法： ClassNode node = new ClassNode(); ClassReader reader =
ifif(firstPar.check() && !Utilities.someOtherCheck(firstPar, secondPar))
ClassNode node = new ClassNode();
ClassReader reader = new ClassReader(bytes); //bytes - original target class
reader.accept(node, 0);
ClassWriter cw = new ClassWriter(0);
node.accept(cw);
MethodVisitor visitor = cw.visitMethod(ACC_PUBLIC, "targetMethod", "<it's signature>", null, null);
visitor.visitCode();
//No idea what to do next
ClassNode节点=新的ClassNode（）；
ClassReader=新的ClassReader（字节）//字节-原始目标类
reader.accept（节点，0）；
ClassWriter cw=新的ClassWriter（0）；
接受节点（cw）；
MethodVisitor=cw.visitMethod（ACC_PUBLIC，“targetMethod”，“问题1可能是最难的。您需要通过识别一些模式来找出插入指令的位置。如果您假设firstPar.check（）
只调用一次，那么您可以为If查找以下字节码指令（firstPar.check（））
：
其中L3
是跳转标签，如果check
returnfalse
对于问题2，请注意if（firstPar.check（）&&！Utilities.someOtherCheck（firstPar，secondPar））
的字节码指令是：
ALOAD 1
INVOKEVIRTUAL Data.check ()Z
IFEQ L3
ALOAD 1
ALOAD 2
INVOKESTATIC Utilities.someOtherCheck (LData;LData;)Z
IFNE L3
因此，您需要在IFEQ L3
之后插入4条新指令
您可以通过使用为targetMethod
创建适配器，方法是子类化ClassVisitor
和MethodNode
：
private static class ClassAdapter extends ClassVisitor {
public ClassAdapter(ClassVisitor cv) {
super(Opcodes.ASM5, cv);
}
@Override
public MethodVisitor visitMethod(int access, String name, String desc,
String signature, String[] exceptions) {
MethodVisitor mv = cv.visitMethod(access, name, desc, signature, exceptions);
if (name.equals("targetMethod"))
return new MethodAdapter(access, name, desc, signature, exceptions, mv);
else
return mv;
}
}
private static class MethodAdapter extends MethodNode {
public MethodAdapter(int access, String name, String desc,
String signature, String[] exceptions, MethodVisitor mv) {
super(Opcodes.ASM5, access, name, desc, signature, exceptions);
this.mv = mv;
}
// More to come ...
}
在MethodAdapter
内部，您可以覆盖visitEnd
以迭代方法内部的所有指令，并尝试检测上述3条指令，并在它们之后插入4条新指令：
@Override
public void visitEnd() {
// Iterates all instructions in the method
ListIterator<AbstractInsnNode> itr = instructions.iterator();
while (itr.hasNext()) {
// Checks whether the instruction is ALOAD 1
AbstractInsnNode node = itr.next();
if (node.getOpcode() != Opcodes.ALOAD
|| ((VarInsnNode) node).var != 1)
continue;
// Checks whether the next instruction is INVOKEVIRTUAL
if (node.getNext() == null
|| node.getNext().getOpcode() != Opcodes.INVOKEVIRTUAL)
continue;
// Checks the invoked method name and signature
MethodInsnNode next = (MethodInsnNode) node.getNext();
if (!next.owner.equals("Data")
|| !next.name.equals("check")
|| !next.desc.equals("()Z"))
continue;
// Checks whether the next of the next instruction is IFEQ
AbstractInsnNode next2 = next.getNext();
if (next2 == null
|| next2.getOpcode() != Opcodes.IFEQ)
continue;
// Creates a list instructions to be inserted
InsnList list = new InsnList();
list.add(new VarInsnNode(Opcodes.ALOAD, 1));
list.add(new VarInsnNode(Opcodes.ALOAD, 2));
list.add(new MethodInsnNode(Opcodes.INVOKESTATIC,
"Utilities", "someOtherCheck",
"(LData;LData;)Z", false));
list.add(new JumpInsnNode(Opcodes.IFNE, ((JumpInsnNode) next2).label));
// Inserts the list, updates maxStack to at least 2, and we are done
instructions.insert(next2, list);
maxStack = Math.max(2, maxStack);
break;
}
accept(mv);
}
谢谢你的回答，效果很好！顺便问一下ClassWriter
构造函数和reader\accept
方法中的零表示什么？没有带0值的标志。这只是默认行为吗？@RedEnergy它们是写和读时的选项。你是对的，0是默认行为。事实上，你刚刚指出了一个bug.：-）我还应该将maxStack
更新为至少2
，以确保堆栈足够大，可以容纳someOtherCheck
的参数。请参见编辑：我添加了一行。
private static class ClassAdapter extends ClassVisitor {
public ClassAdapter(ClassVisitor cv) {
super(Opcodes.ASM5, cv);
}
@Override
public MethodVisitor visitMethod(int access, String name, String desc,
String signature, String[] exceptions) {
MethodVisitor mv = cv.visitMethod(access, name, desc, signature, exceptions);
if (name.equals("targetMethod"))
return new MethodAdapter(access, name, desc, signature, exceptions, mv);
else
return mv;
}
}
private static class MethodAdapter extends MethodNode {
public MethodAdapter(int access, String name, String desc,
String signature, String[] exceptions, MethodVisitor mv) {
super(Opcodes.ASM5, access, name, desc, signature, exceptions);
this.mv = mv;
}
// More to come ...
}
@Override
public void visitEnd() {
// Iterates all instructions in the method
ListIterator<AbstractInsnNode> itr = instructions.iterator();
while (itr.hasNext()) {
// Checks whether the instruction is ALOAD 1
AbstractInsnNode node = itr.next();
if (node.getOpcode() != Opcodes.ALOAD
|| ((VarInsnNode) node).var != 1)
continue;
// Checks whether the next instruction is INVOKEVIRTUAL
if (node.getNext() == null
|| node.getNext().getOpcode() != Opcodes.INVOKEVIRTUAL)
continue;
// Checks the invoked method name and signature
MethodInsnNode next = (MethodInsnNode) node.getNext();
if (!next.owner.equals("Data")
|| !next.name.equals("check")
|| !next.desc.equals("()Z"))
continue;
// Checks whether the next of the next instruction is IFEQ
AbstractInsnNode next2 = next.getNext();
if (next2 == null
|| next2.getOpcode() != Opcodes.IFEQ)
continue;
// Creates a list instructions to be inserted
InsnList list = new InsnList();
list.add(new VarInsnNode(Opcodes.ALOAD, 1));
list.add(new VarInsnNode(Opcodes.ALOAD, 2));
list.add(new MethodInsnNode(Opcodes.INVOKESTATIC,
"Utilities", "someOtherCheck",
"(LData;LData;)Z", false));
list.add(new JumpInsnNode(Opcodes.IFNE, ((JumpInsnNode) next2).label));
// Inserts the list, updates maxStack to at least 2, and we are done
instructions.insert(next2, list);
maxStack = Math.max(2, maxStack);
break;
}
accept(mv);
}
ClassReader reader = new ClassReader("Target");
ClassWriter writer = new ClassWriter(reader, 0);
TraceClassVisitor printer = new TraceClassVisitor(writer,
new PrintWriter(System.getProperty("java.io.tmpdir") + File.separator + "Target.log"));
ClassAdapter adapter = new ClassAdapter(printer);
reader.accept(adapter, 0);
byte[] b = writer.toByteArray(); // The modified bytecode