SpringAOP详解（上）

当需要在方法前后做一些操作就需要借助动态代理来实现

一、动态代理实现方法

1、jdk自带实现方式

jdk实现代理是被代理类实现接口的方式

public interface UserInterface {void test();
}public class UserService implements UserInterface {public void test() {System.out.println("call test method");}}UserService target = new UserService();Object o = Proxy.newProxyInstance(Test.class.getClassLoader(), new Class[]{UserInterface.class}, new InvocationHandler() {@Overridepublic Object invoke(Object proxy, Method method, Object[] args) throws Throwable {System.out.println("test method before");Object invoke = method.invoke(target, args);System.out.println("test method after");return invoke;}});// 只能代理实现UserInterface接口的类，不能强转成UserServiceUserInterface userInterface = (UserInterface)o;userInterface.test();

打印结果：

test method before
call test method
test method after 

必须基于实现接口，产生代理对象类型是UserInterface，而不是UserService

2、基于cglib实现

相比jdk动态代理，cglib不需要修改代码就可以实现动态代理，cglib实现代理是继承被代理类的方式

public class UserService {public void test() {System.out.println("call test method");}public void a() {System.out.println("call test a");}
}UserService target = new UserService();// 通过cglib技术Enhancer enhancer = new Enhancer();enhancer.setSuperclass(UserService.class);// 定义额外逻辑，也就是代理逻辑enhancer.setCallbacks(new Callback[]{new MethodInterceptor() {@Overridepublic Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {System.out.println("before...");Object result = methodProxy.invoke(target, objects);System.out.println("after...");return result;}}, NoOp.INSTANCE});enhancer.setCallbackFilter(new CallbackFilter() {@Overridepublic int accept(Method method) {if (method.getName().equals("test")) {return 0;} else {return 1;}}});// 动态代理所创建出来的UserService对象UserService userService = (UserService) enhancer.create();// 执行这个userService的test方法时，就会额外会执行一些其他逻辑userService.test();// 调用a方法时对应过滤返回的是1，NoOp.INSTANCE是空操作，不会对代理对象做任何操作userService.a();

打印结果：

before...
call test method
after...
call test a

3、spring对jdk和cglib进行封装的ProxyFactory

public class UserService {public void test() {System.out.println("call test method");}
}UserService target = new UserService();ProxyFactory proxyFactory = new ProxyFactory();proxyFactory.setTarget(target);
//		proxyFactory.setInterfaces(UserInterface.class); // jdk动态时设置proxyFactory.addAdvice(new MethodInterceptor() {@Overridepublic Object invoke(MethodInvocation invocation) throws Throwable {System.out.println("before...");Object result = invocation.proceed();System.out.println("after...");return result;}});UserService userService = (UserService) proxyFactory.getProxy();userService.test();

打印结果：

before...
call test method
after...

4、Advice分类

1. Before Advice：方法之前执行
2. After returning advice：方法return后执行
3. After throwing advice：方法抛异常后执行
4. After (finally) advice：方法执行完finally之后执行，这是最后的，比return更后
5. Around advice：这是功能最强大的Advice，可以自定义执行顺序

Before Advice

ProxyFactory proxyFactory = new ProxyFactory();proxyFactory.setTarget(target);
//		proxyFactory.setInterfaces(UserInterface.class); // jdk动态时设置proxyFactory.addAdvice(new TestBeforeAdvice());UserService userService = (UserService) proxyFactory.getProxy();userService.test();public class TestBeforeAdvice implements MethodBeforeAdvice {@Overridepublic void before(Method method, Object[] args, Object target) throws Throwable {System.out.println("方法执行之前");}
}public class UserService {public void test() {System.out.println("call test method");}
}

打印结果：

方法执行之前
call test method 

After returning advice

ProxyFactory proxyFactory = new ProxyFactory();proxyFactory.setTarget(target);
//		proxyFactory.setInterfaces(UserInterface.class); // jdk动态时设置proxyFactory.addAdvice(new TestAfterReturningAdvice());UserService userService = (UserService) proxyFactory.getProxy();userService.test();public class TestAfterReturningAdvice implements AfterReturningAdvice {@Overridepublic void afterReturning(Object returnValue, Method method, Object[] args, Object target) throws Throwable {System.out.println("方法返回之后");}
}public class UserService {public void test() {System.out.println("call test method");}
}

打印结果：

call test method
方法返回之后 

After throwing advice

可根据异常类型在指定异常发生时做对应操作

ProxyFactory proxyFactory = new ProxyFactory();proxyFactory.setTarget(target);
//		proxyFactory.setInterfaces(UserInterface.class); // jdk动态时设置proxyFactory.addAdvice(new TestAfterThrowingAdvice());UserService userService = (UserService) proxyFactory.getProxy();userService.test();public class TestAfterThrowingAdvice implements ThrowsAdvice {public void afterThrowing(Method method, Object[] args, Object target, Exception ex) {System.out.println("方法执行发生异常");}
}public class UserService {public void test() {System.out.println("call test method");throw new RuntimeException();}
}

打印结果：

call test method
方法执行发生异常
Exception in thread "main" java.lang.RuntimeExceptionat com.zhouyu.service.UserService.test(UserService.java:25)at com.zhouyu.service.UserService$$FastClassBySpringCGLIB$$7bfcfe0.invoke(<generated>)at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:791)at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:166)at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:762)at org.springframework.aop.framework.adapter.ThrowsAdviceInterceptor.invoke(ThrowsAdviceInterceptor.java:113)at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:198)at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:762)at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:704)at com.zhouyu.service.UserService$$EnhancerBySpringCGLIB$$e9a0fc71.test(<generated>)at com.zhouyu.Test.main(Test.java:25)

Around advice：

UserService target = new UserService();ProxyFactory proxyFactory = new ProxyFactory();proxyFactory.setTarget(target);
//		proxyFactory.setInterfaces(UserInterface.class); // jdk动态时设置proxyFactory.addAdvice(new TestAroundAdvice());UserService userService = (UserService) proxyFactory.getProxy();userService.test();public class UserService {public void test() {System.out.println("call test method");}
}public class TestAroundAdvice implements MethodInterceptor {@Nullable@Overridepublic Object invoke(@NotNull MethodInvocation invocation) throws Throwable {System.out.println("方法执行之前");Object proceed = invocation.proceed();System.out.println("方法执行之后");return proceed;}
}

打印结果：

方法执行之前
call test method
方法执行之后

上述的Advice只要是UserService类的方法都会被代理执行

5、Advisor

添加自己想执行的执行的方法，下面代码只会执行test方法的Advice代码

public class UserService {public void test() {System.out.println("call test method");}public void a() {System.out.println("call test a");}
}UserService target = new UserService();ProxyFactory proxyFactory = new ProxyFactory();proxyFactory.setTarget(target);
//		proxyFactory.setInterfaces(UserInterface.class); // jdk动态时设置
//		proxyFactory.addAdvice(new TestBeforeAdvice());proxyFactory.addAdvisor(new PointcutAdvisor() {@Overridepublic Pointcut getPointcut() {return new StaticMethodMatcherPointcut() {@Overridepublic boolean matches(Method method, Class<?> targetClass) {if (method.getName().equals("test")) {return true;}return false;}};}@Overridepublic Advice getAdvice() {return new TestBeforeAdvice();}@Overridepublic boolean isPerInstance() {return false;}});UserService userService = (UserService) proxyFactory.getProxy();userService.test();userService.a();

打印结果：

方法执行之前
call test method
call test a

二、ProxyFactoryBean

利用ProxyFactoryBean生成一个代理对象，执行test方法之前执行代理逻辑

public class UserService {public void test() {System.out.println("call test method");}public void a() {System.out.println("call test a");}
}@Beanpublic ProxyFactoryBean userServiceProxy() {ProxyFactoryBean proxyFactoryBean = new ProxyFactoryBean();proxyFactoryBean.setTarget(new UserService());proxyFactoryBean.addAdvice(new TestBeforeAdvice());return proxyFactoryBean;}AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(AppConfig.class);UserService userService = (UserService) applicationContext.getBean("userServiceProxy");userService.test();

打印结果：

方法执行之前
call test method 

三、BeanNameAutoProxyCreator

beanName匹配到的将会自动创建代理对象，根据设置的Advice在调用方法时执行相关代理逻辑（通过beanPostProcessor把Advice添加到一个集合中，当调用调用被代理类时，指定的beanName的方法执行时都会执行代理逻辑）

@Beanpublic BeanNameAutoProxyCreator beanNameAutoProxyCreator() {BeanNameAutoProxyCreator beanNameAutoProxyCreator = new BeanNameAutoProxyCreator();beanNameAutoProxyCreator.setBeanNames("userSe*");beanNameAutoProxyCreator.setInterceptorNames("testBeforeAdvice");beanNameAutoProxyCreator.setProxyTargetClass(true);return beanNameAutoProxyCreator;}@Component
public class TestBeforeAdvice implements MethodBeforeAdvice {@Overridepublic void before(Method method, Object[] args, Object target) throws Throwable {System.out.println("方法执行之前");}
}AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(AppConfig.class);UserService userService = (UserService) applicationContext.getBean("userService");userService.test();

打印结果：

方法执行之前
call test method

四、DefaultAdvisorAutoProxyCreator

// 定义一个advisor@Beanpublic DefaultPointcutAdvisor defaultPointcutAdvisor(){NameMatchMethodPointcut pointcut = new NameMatchMethodPointcut();pointcut.addMethodName("test");DefaultPointcutAdvisor defaultPointcutAdvisor = new DefaultPointcutAdvisor();defaultPointcutAdvisor.setPointcut(pointcut);defaultPointcutAdvisor.setAdvice(new TestBeforeAdvice());return defaultPointcutAdvisor;}// 执行beanPostProcessor时会把advisor添加到一个集合中@Beanpublic DefaultAdvisorAutoProxyCreator defaultAdvisorAutoProxyCreator() {DefaultAdvisorAutoProxyCreator defaultAdvisorAutoProxyCreator = new DefaultAdvisorAutoProxyCreator();return defaultAdvisorAutoProxyCreator;}AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(AppConfig.class);UserService userService = (UserService) applicationContext.getBean("userService");userService.test();

打印结果：

方法执行之前
call test method

五、AOP概念

AspectJ是在编译时对字节码进行了修改，是直接在UserService类对应的字节码中进行增强的，也就是可以理解为是在编译时就会去解析@Before这些注解，然后得到代理逻辑，加入到被代理的类中的字节码中去的，所以如果想用AspectJ技术来生成代理对象 ，是需要用单独的AspectJ编译器的。我们在项目中很少这么用，我们仅仅只是用了@Before这些注解，而我们在启动Spring的过程中，Spring会去解析这些注解，然后利用动态代理机制生成代理对象的。

1. Aspect：表示切面，比如被@Aspect注解的类就是切面，可以在切面中去定义Pointcut、Advice等等
2. Join point：表示连接点，表示一个程序在执行过程中的一个点，比如一个方法的执行，比如一个异常的处理，在Spring AOP中，一个连接点通常表示一个方法的执行。
3. Advice：表示通知，表示在一个特定连接点上所采取的动作。Advice分为不同的类型，后面详细讨论，在很多AOP框架中，包括Spring，会用Interceptor拦截器来实现Advice，并且在连接点周围维护一个Interceptor链
4. Pointcut：表示切点，用来匹配一个或多个连接点，Advice与切点表达式是关联在一起的，Advice将会执行在和切点表达式所匹配的连接点上
5. Introduction：可以使用@DeclareParents来给所匹配的类添加一个接口，并指定一个默认实现
6. Target object：目标对象，被代理对象
7. AOP proxy：表示代理工厂，用来创建代理对象的，在Spring Framework中，要么是JDK动态代理，要么是CGLIB代理
8. Weaving：表示织入，表示创建代理对象的动作，这个动作可以发生在编译时期（比如Aspejctj），或者运行时，比如Spring AOP

​AspectJ定义的几个注解

1. @Before
2. @AfterReturning
3. @AfterThrowing
4. @After
5. @Around