Example code showing how the AdviceAdapter in ASM(.ow2.org) can be used/extended.

ReturnAdapter.java

package self.vpalepu.stackoverflow;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;

import org.objectweb.asm.ClassReader;
import org.objectweb.asm.ClassVisitor;
import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;
import org.objectweb.asm.commons.AdviceAdapter;

/**
 * Class visitor that adapts a java class to insert code before 
 * the return instructions in the methods of the class. 
 * @author vijay
 *
 */
public class ReturnAdapter extends ClassVisitor {
  private String className;

  public ReturnAdapter(ClassVisitor cv, String className) {
    super(Opcodes.ASM4, cv);
  }

  @Override
  public MethodVisitor visitMethod(
      int access,
      String name,
      String desc,
      String signature,
      String[] exceptions) {
    MethodVisitor mv;
    mv = cv.visitMethod(access, name, desc, signature, exceptions);
    mv = new MethodReturnAdapter(Opcodes.ASM4, className, access, name, desc, mv);
    return mv;
  }

  public static void main(String[] args) throws IOException {
    String classFile = args[0];//path of the class file
    String className = args[1];//name of the class
    File inFile = new File(classFile);
    FileInputStream in = new FileInputStream(inFile);

    // adapting the class.
    ClassReader cr = new ClassReader(in);
    ClassWriter cw = new ClassWriter(ClassReader.EXPAND_FRAMES);
    ReturnAdapter returnAdapter = new ReturnAdapter(cw, className); 
    cr.accept(returnAdapter, 0);
  }
}

/**
 * Method Visitor that inserts code right before its return instruction(s),
 * using the onMethodExit(int opcode) method of the AdviceAdapter class, 
 * from ASM(.ow2.org).
 * @author vijay
 *
 */
class MethodReturnAdapter extends AdviceAdapter {
  public MethodReturnAdapter(
      int api,
      String owner,
      int access,
      String name,
      String desc,
      MethodVisitor mv) {
    super(Opcodes.ASM4, mv, access, name, desc);
  }

  public MethodReturnAdapter(
      MethodVisitor mv, 
      int access, 
      String name, 
      String desc) {
    super(Opcodes.ASM4, mv, access, name, desc);
  }

  @Override
  protected void onMethodExit(int opcode) {
    if(opcode != Opcodes.ATHROW) {
      mv.visitVarInsn(Opcodes.ALOAD, 42);
      // and/or any other visit instructions.  
    }
  }
}

I have been busy with paper deadlines these last few weeks. Check back in a couple of days to find better code. Meanwhile, if you want to share the (compile?) error that you are getting, that would be a big help as well!

Can you help me how to use this? I have a class named Hello, it has a method, "sayHello". I did the following in the main method that you have written here.

ByteClassLoader byteClassLoader = new ByteClassLoader();
Class class2 = byteClassLoader.findClass("com.parse.Hello", cw.toByteArray());
System.out.println(class2.getMethods());
System.out.println( ((Hello) class2.newInstance()) .sayHello());
It is showing exception. local variable table overflow in method com.parse.Hello.sayHello()