02-AOP

切点表达式

Joinpoint，织入点，指需要执行代理操作的某个类的某个方法(仅支持方法级别的JoinPoint)；

Pointcut是JoinPoint的表述方式，能捕获JoinPoint。

最常用的切点表达式是AspectJ的切点表达式。需要匹配类，定义ClassFilter接口；匹配方法，定义MethodMatcher接口。PointCut需要同时匹配类和方法，包含ClassFilter和MethodMatcher，AspectJExpressionPointcut是支持AspectJ切点表达式的PointCut实现，简单实现仅支持execution函数。

测试：

public class HelloService {
	public String sayHello() {
		System.out.println("hello");
		return "hello";
	}
}

public class PointcutExpressionTest {

	@Test
	public void testPointcutExpression() throws Exception {
		AspectJExpressionPointcut pointcut = new AspectJExpressionPointcut("execution(* org.springframework.test.service.HelloService.*(..))");
		Class<HelloService> clazz = HelloService.class;
		Method method = clazz.getDeclaredMethod("sayHello");

		assertThat(pointcut.matches(clazz)).isTrue();
		assertThat(pointcut.matches(method, clazz)).isTrue();
	}
}

基于JDK的动态代理

AopProxy是获取代理对象的抽象接口，JdkDynamicAopProxy的基于JDK动态代理的具体实现。TargetSource，被代理对象的封装。MethodInterceptor，方法拦截器，是AOP Alliance的”公民”，顾名思义，可以拦截方法，可在被代理执行的方法前后增加代理行为。

测试;

public class DynamicProxyTest {

	@Test
	public void testJdkDynamicProxy() throws Exception {
		WorldService worldService = new WorldServiceImpl();

		AdvisedSupport advisedSupport = new AdvisedSupport();
		TargetSource targetSource = new TargetSource(worldService);
		WorldServiceInterceptor methodInterceptor = new WorldServiceInterceptor();
		MethodMatcher methodMatcher = new AspectJExpressionPointcut("execution(* org.springframework.test.service.WorldService.explode(..))").getMethodMatcher();
		advisedSupport.setTargetSource(targetSource);
		advisedSupport.setMethodInterceptor(methodInterceptor);
		advisedSupport.setMethodMatcher(methodMatcher);

		WorldService proxy = (WorldService) new JdkDynamicAopProxy(advisedSupport).getProxy();
		proxy.explode();
	}
}

基于CGLIB的动态代理

基于CGLIB的动态代理实现逻辑也比较简单，查看CglibAopProxy。与基于JDK的动态代理在运行期间为接口生成对象的代理对象不同，基于CGLIB的动态代理能在运行期间动态构建字节码的class文件，为类生成子类，因此被代理类不需要继承自任何接口。

测试：

public class DynamicProxyTest {

	private AdvisedSupport advisedSupport;

	@Before
	public void setup() {
		WorldService worldService = new WorldServiceImpl();

		advisedSupport = new AdvisedSupport();
		TargetSource targetSource = new TargetSource(worldService);
		WorldServiceInterceptor methodInterceptor = new WorldServiceInterceptor();
		MethodMatcher methodMatcher = new AspectJExpressionPointcut("execution(* org.springframework.test.service.WorldService.explode(..))").getMethodMatcher();
		advisedSupport.setTargetSource(targetSource);
		advisedSupport.setMethodInterceptor(methodInterceptor);
		advisedSupport.setMethodMatcher(methodMatcher);
	}

	@Test
	public void testCglibDynamicProxy() throws Exception {
		WorldService proxy = (WorldService) new CglibAopProxy(advisedSupport).getProxy();
		proxy.explode();
	}
}

AOP代理工厂ProxyFactory

增加AOP代理工厂ProxyFactory，由AdvisedSupport#proxyTargetClass属性决定使用JDK动态代理还是CGLIB动态代理。

测试：

public class DynamicProxyTest {

	private AdvisedSupport advisedSupport;

	@Before
	public void setup() {
		WorldService worldService = new WorldServiceImpl();

		advisedSupport = new AdvisedSupport();
		TargetSource targetSource = new TargetSource(worldService);
		WorldServiceInterceptor methodInterceptor = new WorldServiceInterceptor();
		MethodMatcher methodMatcher = new AspectJExpressionPointcut("execution(* org.springframework.test.service.WorldService.explode(..))").getMethodMatcher();
		advisedSupport.setTargetSource(targetSource);
		advisedSupport.setMethodInterceptor(methodInterceptor);
		advisedSupport.setMethodMatcher(methodMatcher);
	}

	@Test
	public void testProxyFactory() throws Exception {
		// 使用JDK动态代理
		advisedSupport.setProxyTargetClass(false);
		WorldService proxy = (WorldService) new ProxyFactory(advisedSupport).getProxy();
		proxy.explode();

		// 使用CGLIB动态代理
		advisedSupport.setProxyTargetClass(true);
		proxy = (WorldService) new ProxyFactory(advisedSupport).getProxy();
		proxy.explode();
	}
}

几种常用的Advice：BeforeAdvice/AfterAdvice/AfterReturningAdvice/ThrowsAdvice…

Spring将AOP联盟中的Advice细化出各种类型的Advice，常用的有BeforeAdvice/AfterAdvice/AfterReturningAdvice/ThrowsAdvice，我们可以通过扩展MethodInterceptor来实现。

只简单实现BeforeAdvice，有兴趣的同学可以帮忙实现另外几种Advice。定义MethodBeforeAdviceInterceptor拦截器，在执行被代理方法之前，先执行BeforeAdvice的方法。

BeforeAdvice
AfterAdvice
AfterReturningAdvice
ThrowsAdvice

测试：

public class WorldServiceBeforeAdvice implements MethodBeforeAdvice {

	@Override
	public void before(Method method, Object[] args, Object target) throws Throwable {
		System.out.println("BeforeAdvice: do something before the earth explodes");
	}
}

public class DynamicProxyTest {

	private AdvisedSupport advisedSupport;

	@Before
	public void setup() {
		WorldService worldService = new WorldServiceImpl();

		advisedSupport = new AdvisedSupport();
		TargetSource targetSource = new TargetSource(worldService);
		MethodMatcher methodMatcher = new AspectJExpressionPointcut("execution(* org.springframework.test.service.WorldService.explode(..))").getMethodMatcher();
		advisedSupport.setTargetSource(targetSource);
		advisedSupport.setMethodMatcher(methodMatcher);
	}

	@Test
	public void testBeforeAdvice() throws Exception {
		//设置BeforeAdvice
		WorldServiceBeforeAdvice beforeAdvice = new WorldServiceBeforeAdvice();
		MethodBeforeAdviceInterceptor methodInterceptor = new MethodBeforeAdviceInterceptor(beforeAdvice);
		advisedSupport.setMethodInterceptor(methodInterceptor);

		WorldService proxy = (WorldService) new ProxyFactory(advisedSupport).getProxy();
		proxy.explode();
	}
}

PointcutAdvisor：Pointcut和Advice的组合

Advisor是包含一个Pointcut和一个Advice的组合，Pointcut用于捕获JoinPoint，Advice决定在JoinPoint执行某种操作。实现了一个支持aspectj表达式的AspectJExpressionPointcutAdvisor。

测试：

public class DynamicProxyTest {

	@Test
	public void testAdvisor() throws Exception {
		WorldService worldService = new WorldServiceImpl();

		//Advisor是Pointcut和Advice的组合
		String expression = "execution(* org.springframework.test.service.WorldService.explode(..))";
		AspectJExpressionPointcutAdvisor advisor = new AspectJExpressionPointcutAdvisor();
		advisor.setExpression(expression);
		MethodBeforeAdviceInterceptor methodInterceptor = new MethodBeforeAdviceInterceptor(new WorldServiceBeforeAdvice());
		advisor.setAdvice(methodInterceptor);

		ClassFilter classFilter = advisor.getPointcut().getClassFilter();
		if (classFilter.matches(worldService.getClass())) {
			AdvisedSupport advisedSupport = new AdvisedSupport();
			TargetSource targetSource = new TargetSource(worldService);
			advisedSupport.setTargetSource(targetSource);
			advisedSupport.setMethodInterceptor((MethodInterceptor) advisor.getAdvice());
			advisedSupport.setMethodMatcher(advisor.getPointcut().getMethodMatcher());
//			advisedSupport.setProxyTargetClass(true);   //JDK or CGLIB

			WorldService proxy = (WorldService) new ProxyFactory(advisedSupport).getProxy();
			proxy.explode();
		}
	}
}

动态代理融入bean生命周期

结合前面讲解的bean的生命周期，BeanPostProcessor处理阶段可以修改和替换bean，正好可以在此阶段返回代理对象替换原对象。不过我们引入一种特殊的BeanPostProcessor——InstantiationAwareBeanPostProcessor，如果InstantiationAwareBeanPostProcessor处理阶段返回代理对象，会导致短路，不会继续走原来的创建bean的流程，具体实现查看AbstractAutowireCapableBeanFactory#resolveBeforeInstantiation。

DefaultAdvisorAutoProxyCreator是处理横切逻辑的织入返回代理对象的InstantiationAwareBeanPostProcessor实现类，当对象实例化时，生成代理对象并返回。

至此，bean的生命周期如下：

测试： auto-proxy.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
	         http://www.springframework.org/schema/beans/spring-beans.xsd
		 http://www.springframework.org/schema/context
		 http://www.springframework.org/schema/context/spring-context-4.0.xsd">

    <bean id="worldService" class="org.springframework.test.service.WorldServiceImpl"/>

    <bean class="org.springframework.aop.framework.autoproxy.DefaultAdvisorAutoProxyCreator"/>

    <bean id="pointcutAdvisor" class="org.springframework.aop.aspectj.AspectJExpressionPointcutAdvisor">
        <property name="expression" value="execution(* org.springframework.test.service.WorldService.explode(..))"/>
        <property name="advice" ref="methodInterceptor"/>
    </bean>


    <bean id="methodInterceptor" class="org.springframework.aop.framework.adapter.MethodBeforeAdviceInterceptor">
        <property name="advice" ref="beforeAdvice"/>
    </bean>

    <bean id="beforeAdvice" class="org.springframework.test.common.WorldServiceBeforeAdvice"/>

</beans>

public class AutoProxyTest {

	@Test
	public void testAutoProxy() throws Exception {
		ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:auto-proxy.xml");

		//获取代理对象
		WorldService worldService = applicationContext.getBean("worldService", WorldService.class);
		worldService.explode();
	}
}