why the field can't be printed and so many redundancy

lucefe <[email protected]> Thu, 15 Jul 2010 09:45:08 +0800

Newsgroups	gmane.comp.java.objectweb.asm
Message-ID	<[email protected]>

*Hi, everybody,

    I want to instrument a method：*
* from*
   public void m() throws Exception{
        Thread.sleep(100);
    }

*to*

    public void m() throws Exception{
        timer -= System.currentTimeMillis();
        Thread.sleep(100);
        timer += System.currentTimeMillis();
        System.out.println(timer);
    }

*my classAdapter is attached, when I use the next code:*

ByteArrayOutputStream stream = new ByteArrayOutputStream();
                PrintWriter printWriter = new PrintWriter(stream);
                ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_MAXS);
                TraceClassVisitor tcv = new TraceClassVisitor(cw,
printWriter);
                AddTimerAdapter ca = new AddTimerAdapter(tcv);
                AddTimerMethodAdapter ma =
ca.visitMethod(Opcodes.ACC_PUBLIC, "m", "()V", null, null);
                ma.visitCode();
                ma.visitInsn(Opcodes.RETURN);
                ma.visitMaxs(4, 1);
                ma.visitEnd();
                ca.visitEnd();
                cr.accept(ca, ClassReader.SKIP_DEBUG);
                System.out.println(stream);

*I got the following result. There were so many redundancy, and the field
timer was not printed as I wanted. who can tell me where is my error.*

// class version 49.0 (49)
// access flags 33
public class pkg/C {


  // access flags 9
  public static J timer

  // access flags 1
  public <init>()V

  // access flags 1
  public m()V throws java/lang/Exception
    GETSTATIC pkg/C.timer : J
    INVOKESTATIC java/lang/System.currentTimeMillis ()J
    LSUB
    PUTSTATIC pkg/C.timer : J
    GETSTATIC pkg/C.timer : J
    INVOKESTATIC java/lang/System.currentTimeMillis ()J
    LSUB
    PUTSTATIC pkg/C.timer : J
    LDC 100
    INVOKESTATIC java/lang/Thread.sleep (J)V
    GETSTATIC pkg/C.timer : J
    INVOKESTATIC java/lang/System.currentTimeMillis ()J
    LADD
    PUTSTATIC pkg/C.timer : J
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    GETSTATIC pkg/C.timer : J
    INVOKEVIRTUAL java/io/PrintStream.println (J)V
    GETSTATIC pkg/C.timer : J
    INVOKESTATIC java/lang/System.currentTimeMillis ()J
    LADD
    PUTSTATIC pkg/C.timer : J
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    GETSTATIC pkg/C.timer : J
    INVOKEVIRTUAL java/io/PrintStream.println (J)V
    RETURN
    MAXSTACK = 8
    MAXLOCALS = 1

  // access flags 9
  public static J timer
}

AddTimerAdapter.java (text/x-java, 3.1 KB)

package ch3;

import static org.objectweb.asm.Opcodes.ACC_INTERFACE;
import static org.objectweb.asm.Opcodes.ACC_PUBLIC;
import static org.objectweb.asm.Opcodes.ACC_STATIC;
import static org.objectweb.asm.Opcodes.ATHROW;
import static org.objectweb.asm.Opcodes.GETSTATIC;
import static org.objectweb.asm.Opcodes.INVOKESTATIC;
import static org.objectweb.asm.Opcodes.INVOKEVIRTUAL;
import static org.objectweb.asm.Opcodes.IRETURN;
import static org.objectweb.asm.Opcodes.LADD;
import static org.objectweb.asm.Opcodes.LSUB;
import static org.objectweb.asm.Opcodes.PUTSTATIC;
import static org.objectweb.asm.Opcodes.RETURN;

import org.objectweb.asm.ClassAdapter;
import org.objectweb.asm.ClassVisitor;
import org.objectweb.asm.FieldVisitor;
import org.objectweb.asm.MethodAdapter;
import org.objectweb.asm.MethodVisitor;

/**
 * ASM Guide example class.
 * 
 * @author Eric Bruneton
 */
public class AddTimerAdapter extends ClassAdapter {

  private String owner;

  private boolean isInterface;

  public AddTimerAdapter(ClassVisitor cv) {
    super(cv);
  }

  public void visit(int version, int access, String name,
      String signature, String superName, String[] interfaces) {
    cv.visit(version, access, name, signature, superName, interfaces);
    owner = name;
    isInterface = (access & ACC_INTERFACE) != 0;
  }

  public AddTimerMethodAdapter visitMethod(int access, String name,
      String desc, String signature, String[] exceptions) {
    MethodVisitor mv = cv.visitMethod(access, name, desc, signature,
        exceptions);
    AddTimerMethodAdapter ma;
    if (!isInterface && mv != null && !name.equals("<init>")) {
      ma = new AddTimerMethodAdapter(mv);
      return ma;
    }
    return null;
  }

  public void visitEnd() {
    if (!isInterface) {
      FieldVisitor fv = cv.visitField(ACC_PUBLIC + ACC_STATIC, "timer",
          "J", null, null);
      if (fv != null) {
        fv.visitEnd();
      }
    }
    cv.visitEnd();
  }

  public class AddTimerMethodAdapter extends MethodAdapter {

    public AddTimerMethodAdapter(MethodVisitor mv) {
      super(mv);
    }

    public void visitCode() {
      mv.visitCode();
      mv.visitFieldInsn(GETSTATIC, owner, "timer", "J");
      mv.visitMethodInsn(INVOKESTATIC, "java/lang/System",
          "currentTimeMillis", "()J");
      mv.visitInsn(LSUB);
      mv.visitFieldInsn(PUTSTATIC, owner, "timer", "J");
    }

    public void visitInsn(int opcode) {
      if ((opcode == IRETURN || opcode == RETURN) || opcode == ATHROW) {
        mv.visitFieldInsn(GETSTATIC, owner, "timer", "J");
        mv.visitMethodInsn(INVOKESTATIC, "java/lang/System",
            "currentTimeMillis", "()J");
        mv.visitInsn(LADD);
        mv.visitFieldInsn(PUTSTATIC, owner, "timer", "J");
        mv.visitFieldInsn(GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;");
        mv.visitFieldInsn(GETSTATIC, owner, "timer", "J");
        mv.visitMethodInsn(INVOKEVIRTUAL, "java/io/PrintStream", "println", "(J)V");
        
      }
      mv.visitInsn(opcode);
    }

    public void visitMaxs(int maxStack, int maxLocals) {
      mv.visitMaxs(maxStack + 4, maxLocals);
    }
  }
}

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