AOP系列（四） SpringAOP中的代理机制

在运行时,通过某种方法动态生成代理类.class文件,比较常见技术就是JAVA动态代理和Cglib代理。

分类

JAVA动态代理技术

必须定义一个接口

public interface Animal {

    void  eat(String food);
}
复制代码

实现类Cat

public class Cat implements Animal {


    @Override
    public void eat(String food) {
        System.out.println(Cat.class.getSimpleName()+" eat:"+food);
    }
}
复制代码

实现类Dog

public class Dog implements Animal {


    @Override
    public void eat(String food) {
        System.out.println(Dog.class.getSimpleName()+" eat:"+food);
    }
}

复制代码

public class AnimalHandler implements InvocationHandler {

    private Animal target;

    public AnimalHandler(Animal target) {
        this.target = target;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        before();
        //这里可以修改参数
        StringBuilder  stringBuilder=new StringBuilder();
        for (int i = 0; i < args.length; i++) {
            stringBuilder.append("param"+(i+1)+":"+args[i]).append(",");
        }
        if (stringBuilder.length()>1){
            System.out.println(stringBuilder.subSequence(0,stringBuilder.length()-1));
        }
        System.out.println("method："+method.getName());
        Object ret=method.invoke(target,args);
        after();
        return ret;
    }

    /**
     * 方法执行前
     */
    private void before() {
        System.out.println("方法执行前 !");
    }

    /**
     * 方法执行后
     */
    private void after() {
        System.out.println("方法执行后");
    }

}
复制代码

测试生成代理类

public static void main(String[] args) {
        System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");

        Animal cat = new Cat();
        //找到代理对象
        Animal catProxy = (Animal) Proxy.newProxyInstance(Cat.class.getClassLoader(), new Class[]{Animal.class}, new AnimalHandler(cat));
        System.out.println(catProxy.getClass().getSimpleName());
        catProxy.eat("猫粮");

        Animal dog = new Dog();
        Animal dogProxy = (Animal) Proxy.newProxyInstance(Dog.class.getClassLoader(), new Class[]{Animal.class}, new AnimalHandler(dog));
        System.out.println(dogProxy.getClass().getSimpleName());

        dogProxy.eat("狗粮");
    }
复制代码

输出结果：

$Proxy0
方法执行前 !
param1:猫粮
method：eat
Cat eat:猫粮
方法执行后
$Proxy0
方法执行前 !
param1:狗粮
method：eat
Dog eat:狗粮
方法执行后
复制代码

System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true"),这句话会在本地生成代理类文件。

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package com.sun.proxy;

import com.yuntian.firstspringboot.proxy.Animal;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.lang.reflect.UndeclaredThrowableException;

public final class $Proxy0 extends Proxy implements Animal {
    private static Method m1;
    private static Method m2;
    private static Method m3;
    private static Method m0;

    public $Proxy0(InvocationHandler var1) throws  {
        super(var1);
    }

    public final boolean equals(Object var1) throws  {
        try {
            return (Boolean)super.h.invoke(this, m1, new Object[]{var1});
        } catch (RuntimeException | Error var3) {
            throw var3;
        } catch (Throwable var4) {
            throw new UndeclaredThrowableException(var4);
        }
    }

    public final String toString() throws  {
        try {
            return (String)super.h.invoke(this, m2, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }

    public final void eat(String var1) throws  {
        try {
            super.h.invoke(this, m3, new Object[]{var1});
        } catch (RuntimeException | Error var3) {
            throw var3;
        } catch (Throwable var4) {
            throw new UndeclaredThrowableException(var4);
        }
    }

    public final int hashCode() throws  {
        try {
            return (Integer)super.h.invoke(this, m0, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }

    static {
        try {
            m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object"));
            m2 = Class.forName("java.lang.Object").getMethod("toString");
            m3 = Class.forName("com.yuntian.firstspringboot.proxy.Animal").getMethod("eat", Class.forName("java.lang.String"));
            m0 = Class.forName("java.lang.Object").getMethod("hashCode");
        } catch (NoSuchMethodException var2) {
            throw new NoSuchMethodError(var2.getMessage());
        } catch (ClassNotFoundException var3) {
            throw new NoClassDefFoundError(var3.getMessage());
        }
    }
}

复制代码

• 生成代理类对象

Proxy.newProxyInstance(Cat.class.getClassLoader(), new Class[]{Animal.class}, new AnimalHandler(cat));
复制代码

• 寻找代理类，先从缓存中寻找

private static final WeakCache<ClassLoader, Class<?>[], Class<?>>
        proxyClassCache = new WeakCache<>(new KeyFactory(), new ProxyClassFactory());


 Class<?> cl = getProxyClass0(loader, intfs);
复制代码

分析这句代码和上面执行流程,参数有类加载器classloader、接口类、Handler实现类。源码分析,可以晓得生成一个代理类,然后反射获取接口的全部方法,并实现方法,再通过h.invoke()方法,调用原对象的方法。

cglib动态代理技术

这里可以定义接口或者类

public abstract class AbstartAnimal {

    public abstract void eat(String food);

}
复制代码

public class CatTest extends AbstartAnimal {


    @Override
    public void eat(String food) {
        System.out.println(CatTest.class.getSimpleName()+" eat:"+food);
    }
}

复制代码

public class DogTest extends AbstartAnimal {


    @Override
    public void eat(String food) {
        System.out.println(DogTest.class.getSimpleName()+" eat:"+food);
    }
}

复制代码

定义方法拦截器

import org.springframework.cglib.proxy.Enhancer;
import org.springframework.cglib.proxy.MethodInterceptor;
import org.springframework.cglib.proxy.MethodProxy;

import java.lang.reflect.Method;

public class AbstratAnimalInterceptor implements MethodInterceptor {

    /**
     * 被增强的类
     */
    private AbstartAnimal target;

    public AbstratAnimalInterceptor(AbstartAnimal target) {
        super();
        this.target = target;
    }

    /**
     * 用来产生代理对象
     */
    public  Object createProxy() {
        // 增强类
        Enhancer enhancer = new Enhancer();
        // 设置增强类的回调方法
        enhancer.setCallback(this);
        //设置代理类的父类
        enhancer.setSuperclass(AbstartAnimal.class);
        return enhancer.create();
    }


    @Override
    public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
        before();
        Object ret = method.invoke(target, objects);
        after();
        return ret;
    }


    /**
     * 方法执行前
     */
    private void before() {
        System.out.println("方法执行前 !");
    }

    /**
     * 方法执行后
     */
    private void after() {
        System.out.println("方法执行后");
    }


}
复制代码

测试方法：

@Test
    public void testcglibProxy() {

        AbstartAnimal cat = new CatTest();
        AbstratAnimalInterceptor interceptorCat = new AbstratAnimalInterceptor(cat);
        AbstartAnimal catProxy = (AbstartAnimal) interceptorCat.createProxy();
        catProxy.eat("猫粮");

        AbstartAnimal dog = new DogTest();
        AbstratAnimalInterceptor interceptorDog = new AbstratAnimalInterceptor(dog);
        AbstartAnimal dogProxy = (AbstartAnimal) interceptorDog.createProxy();
        dogProxy.eat("狗粮");
    }

复制代码

输出：

方法执行前 !
CatTest eat:猫粮
方法执行后
方法执行前 !
DogTest eat:狗粮
方法执行后
复制代码

三、比较代理方式

在Spring中使用代理技术只有JAVA动态代理和Cglib代理,此外生成代理类技术还有JAVAASSIST和ASM。