package com.asm3;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.Opcodes;

/**
 * 通过asm生成类的字节码
 * @author Administrator
 *
 */
public class GeneratorClass {

 public static void main(String[] args) throws IOException {
 //生成一个类只需要ClassWriter组件即可
 ClassWriter cw = new ClassWriter(0);
 //通过visit方法确定类的头部信息
 cw.visit(Opcodes.V1_5, Opcodes.ACC_PUBLIC+Opcodes.ACC_ABSTRACT+Opcodes.ACC_INTERFACE,
  "com/asm3/Comparable", null, "java/lang/Object", new String[]{"com/asm3/Mesurable"});
 //定义类的属性
 cw.visitField(Opcodes.ACC_PUBLIC+Opcodes.ACC_FINAL+Opcodes.ACC_STATIC,
  "LESS", "I", null, new Integer(-1)).visitEnd();
 cw.visitField(Opcodes.ACC_PUBLIC+Opcodes.ACC_FINAL+Opcodes.ACC_STATIC,
  "EQUAL", "I", null, new Integer(0)).visitEnd();
 cw.visitField(Opcodes.ACC_PUBLIC+Opcodes.ACC_FINAL+Opcodes.ACC_STATIC,
  "GREATER", "I", null, new Integer(1)).visitEnd();
 //定义类的方法
 cw.visitMethod(Opcodes.ACC_PUBLIC+Opcodes.ACC_ABSTRACT, "compareTo",
  "(Ljava/lang/Object;)I", null, null).visitEnd();
 cw.visitEnd(); //使cw类已经完成
 //将cw转换成字节数组写到文件里面去
 byte[] data = cw.toByteArray();
 File file = new File("D://Comparable.class");
 FileOutputStream fout = new FileOutputStream(file);
 fout.write(data);
 fout.close();
 }
}

public interface com.asm3.Comparable extends com.asm3.Mesurable {
 public static final int LESS;

 public static final int EQUAL;

 public static final int GREATER;

 public abstract int compareTo(java.lang.Object);
}

package com.asm5;

public class C {
 public void m() throws InterruptedException{
 Thread.sleep(100); 
 }
}

package com.asm5;

public class C {
 public static long timer;
 public void m() throws InterruptedException{
 timer -= System.currentTimeMillis();
 Thread.sleep(100); 
 timer += System.currentTimeMillis();
 }
}

package com.asm5;

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;
import org.objectweb.asm.Opcodes;

public class AddTimeClassAdapter extends ClassAdapter {
 private String owner;
 private boolean isInterface;
 public AddTimeClassAdapter(ClassVisitor cv) {
 super(cv);
 }
 @Override
 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 & Opcodes.ACC_INTERFACE) != 0;
 }
 @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("<init>") && !isInterface && mv!=null){
  //为方法添加计时功能
  mv = new AddTimeMethodAdapter(mv);
 }
 return mv;
 }
 @Override
 public void visitEnd() {
 //添加字段
 if(!isInterface){
  FieldVisitor fv = cv.visitField(Opcodes.ACC_PUBLIC+Opcodes.ACC_STATIC, "timer", "J", null, null);
  if(fv!=null){
  fv.visitEnd();
  }
 }
 cv.visitEnd();
 }
 
 class AddTimeMethodAdapter extends MethodAdapter{
 public AddTimeMethodAdapter(MethodVisitor mv) {
  super(mv);
 }
 @Override
 public void visitCode() {
  mv.visitCode();
  mv.visitFieldInsn(Opcodes.GETSTATIC, owner, "timer", "J");
  mv.visitMethodInsn(Opcodes.INVOKESTATIC, "java/lang/System", "currentTimeMillis", "()J");
  mv.visitInsn(Opcodes.LSUB);
  mv.visitFieldInsn(Opcodes.PUTSTATIC, owner, "timer", "J");
 }
 @Override
 public void visitInsn(int opcode) {
  if((opcode>=Opcodes.IRETURN && opcode<=Opcodes.RETURN) || opcode==Opcodes.ATHROW){
  mv.visitFieldInsn(Opcodes.GETSTATIC, owner, "timer", "J");
  mv.visitMethodInsn(Opcodes.INVOKESTATIC, "java/lang/System", "currentTimeMillis", "()J");
  mv.visitInsn(Opcodes.LADD);
  mv.visitFieldInsn(Opcodes.PUTSTATIC, owner, "timer", "J");
  }
  mv.visitInsn(opcode);
 }
 @Override
 public void visitMaxs(int maxStack, int maxLocal) {
  mv.visitMaxs(maxStack+4, maxLocal);
 }
 }
 
}

package com.asm5;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

import org.objectweb.asm.ClassAdapter;
import org.objectweb.asm.ClassReader;
import org.objectweb.asm.ClassWriter;



public class Generator {

 public static void main(String[] args){
 try {
  ClassReader cr = new ClassReader("com/asm5/C");
  ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_MAXS);
  ClassAdapter classAdapter = new AddTimeClassAdapter(cw);
  //使给定的访问者访问Java类的ClassReader
  cr.accept(classAdapter, ClassReader.SKIP_DEBUG);
  byte[] data = cw.toByteArray();
  File file = new File(System.getProperty("user.dir") + "\\WebRoot\\WEB-INF\\classes\\com\\asm5\\C.class");
  FileOutputStream fout = new FileOutputStream(file);
  fout.write(data);
  fout.close();
  System.out.println("success!");
 } catch (FileNotFoundException e) {
  e.printStackTrace();
 } catch (IOException e) {
  e.printStackTrace();
 }
 }

}

package com.asm5;

public class Test {
 public static void main(String[] args) throws InterruptedException, NoSuchFieldException, SecurityException, IllegalArgumentException, IllegalAccessException {
 C c = new C();
 c.m();
 Class cc = c.getClass();
 System.out.println(cc.getField("timer").get(c));
 }
}