使用ASM4.0实现AOP的功能，监控每个方法的执行时间

AOP的更通用的做法是对原始类动态生成子类，调用子类的方法覆盖父类，来实现AOP的功能。著名的 Hibernate 和 Spring 框架，就是使用这种技术实现了 AOP 的“无损注入”。

下面我们就通过一个示例来对方法Foo.execute调用时动态注入方法执行前后的时间统计来统计方法的执行时间

[java]
import java.io.FileOutputStream;
import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

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;

public class AsmAopExample extends ClassLoader implements Opcodes{

    public static class Foo {
        public static void execute() {
            System.out.println("test changed method name");
            try {
                Thread.sleep(10);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }

    public static class Monitor{

        static long start = 0;

        public static void start(){
            start = System.currentTimeMillis();
        }
        public static void end(){
            long end = System.currentTimeMillis();
            System.out.println("execute method use time :" + (end - start));
        }
    }

    public static void main(String[] args) throws IOException, IllegalArgumentException, SecurityException, IllegalAccessException, InvocationTargetException {

        ClassReader cr = new ClassReader(Foo.class.getName());
        ClassWriter cw = new ClassWriter(cr, ClassWriter.COMPUTE_MAXS);
        ClassVisitor cv = new MethodChangeClassAdapter(cw);
        cr.accept(cv, Opcodes.ASM4);

        // gets the bytecode of the Example class, and loads it dynamically
        byte[] code = cw.toByteArray();

        AsmAopExample loader = new AsmAopExample();
        Class<?> exampleClass = loader.defineClass(Foo.class.getName(), code, 0, code.length);

        for(Method method: exampleClass.getMethods()){
            System.out.println(method);
        }

        exampleClass.getMethods()[0].invoke(null, null); //調用execute，修改方法內容


        // gets the bytecode of the Example class, and loads it dynamically

        FileOutputStream fos = new FileOutputStream("e:\\logs\\Example.class");
        fos.write(code);
        fos.close();
    }

    static class MethodChangeClassAdapter extends ClassVisitor implements Opcodes {

        public MethodChangeClassAdapter(final ClassVisitor cv) {
            super(Opcodes.ASM4, cv);
        }

        @Override
        public MethodVisitor visitMethod(
            int access,
            String name,
            String desc,
            String signature,
            String[] exceptions)
        {
            if("execute".equals(name)) //此处的execute即为需要修改的方法，修改方法內容
            {
                MethodVisitor mv = cv.visitMethod(access, name, desc, signature, exceptions);//先得到原始的方法
                MethodVisitor newMethod = null;
                newMethod = new AsmMethodVisit(mv); //访问需要修改的方法
                return newMethod;
            }

            return null;
        }

    }

     static class AsmMethodVisit extends MethodVisitor {

        public AsmMethodVisit(MethodVisitor mv) {
            super(Opcodes.ASM4, mv);
&nb

补充：软件开发 , Java ,