在ASM字节码中漂亮地打印方法

Question

我正在尝试（没有成功） 仅 打印给定方法的内容。以下代码 几乎 可以解决问题：

    class MyTraceMethodVisitor extends MethodVisitor {
        public MyTraceMethodVisitor(MethodVisitor mv) {
            super(Opcodes.ASM4, mv);
        }

        @Override
        public void visitMaxs(int maxStack, int maxLocals) {
        }
    }

    class MyClassVisitor extends ClassVisitor {
        public MyClassVisitor(ClassVisitor cv) {
            super(Opcodes.ASM4, cv);
        }

        @Override
        public FieldVisitor visitField(int access, String name, String desc,
                String signature, Object value) {
            return null;
        }

        @Override
        public MethodVisitor visitMethod(int access, String name, String desc,
                String signature, String[] exceptions) {

            if (name.equals("get777"))
                return new MyTraceMethodVisitor(super.visitMethod(access, name, desc, signature, exceptions));

            return null;
        }
    }

用它运行

ClassReader classReader = new ClassReader("something.Point");
PrintWriter printWriter = new PrintWriter(System.out);
TraceClassVisitor traceClassVisitor = new TraceClassVisitor(printWriter);
MyClassVisitor myClassVisitor = new MyClassVisitor(traceClassVisitor);
classReader.accept(myClassVisitor, ClassReader.SKIP_DEBUG);

导致

// class version 50.0 (50)
// access flags 0x21
public class something/Point {


  // access flags 0x1
  public get777()I
    SIPUSH 777
    IRETURN
}

我想要得到的只是

    SIPUSH 777
    IRETURN

没有签名，评论等任何内容。我该怎么做？

Answer 1

答案已经很老了，涉及编写很多代码。

从asm v5开始，打印方法说明很简单：

// Setup for asm ClassReader, ClassWriter and your implementation of the ClassVisitor(e.g.: YourClassVisitor)
final ClassReader reader = new ClassReader(classBytes);
final ClassWriter writer = new ClassWriter(classReader, ClassWriter.COMPUTE_MAXS);
final ClassVisitor visitor =new YourClassVisitor(Opcodes.ASM5, visitor);

在实现ClassVisitor时，只需覆盖visitMethod方法。这里是一个例子：

public class YourClassVisitor extends ClassVisitor {
    public InstrumentationClassVisitor(int api, ClassVisitor cv) {
        super(api, cv);
    }

    @Override
    public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions) {
        MethodVisitor mv = cv.visitMethod(access, name, desc, signature, exceptions);
        Printer p = new Textifier(Opcodes.ASM5) {
            @Override
            public void visitMethodEnd() {
                print(new PrintWriter(System.out)); // print it after it has been visited
            }
        };
        return new TraceMethodVisitor(mv, p);
    }
}

TraceMethodVisitor将由classVisitor接收事件调用，以访问方法说明等。然后，TraceMethodVisitor将在打印机的帮助下打印代码。