Spring AOP:理解动态代理和 Advice

ProxyFactory

cglib代理解析
jdk动态代理

动态代理技术在Spring中进行了封装,封装出来的类叫做ProxyFactory,表示是创建一个代理对象的一个工厂,比jdk动态代理和cglib代理更加方便,比如:

public class UserService {

    public void test(){
        System.out.println("test...");
        throw new RuntimeException("111");
    }
}

public class Demo {

    public static void main(String[] args) {
        UserService userService = new UserService();
        ProxyFactory proxyFactory = new ProxyFactory();
        proxyFactory.setTarget(userService);
        proxyFactory.addAdvice((MethodInterceptor) invocation -> {
            System.out.println("before...");
            Object proceed = invocation.proceed();
            System.out.println("after...");
            return proceed;
        });
        UserService proxy = (UserService) proxyFactory.getProxy();
        proxy.test();
    }
}

Spring AOP:理解动态代理和 Advice_第1张图片

通过ProxyFactory,我们可以不在关心到底是用cglib还是jdk动态代理了,ProxyFactory会帮我们去判断,如果UserService实现了接口,那么ProxyFactory底层就会用jdk动态代理,如果没有实现接口,就会用cglib技术.

Advice的分类

  1. BeforeAdvice:方法之前执行

    public class MethodBeforeAdviceImpl implements MethodBeforeAdvice {
    
        @Override
        public void before(Method method, Object[] args, Object target) throws Throwable {
            System.out.println("方法执行前执行...");
        }
    }
    
    public class Demo {
    
        public static void main(String[] args) {
            UserService userService = new UserService();
            ProxyFactory proxyFactory = new ProxyFactory();
            proxyFactory.setTarget(userService);
            proxyFactory.addAdvice(new MethodBeforeAdviceImpl());
            UserService proxy = (UserService) proxyFactory.getProxy();
            proxy.test();
        }
    }
    

Spring AOP:理解动态代理和 Advice_第2张图片

  1. AfterReturningAdvice:方法return后执行

    public class AfterReturningAdviceImpl implements AfterReturningAdvice {
    
        @Override
        public void afterReturning(Object returnValue, Method method, Object[] args, Object target) throws Throwable {
            System.out.println("方法return后执行");
        }
    }
    
    public class Demo {
    
        public static void main(String[] args) {
            UserService userService = new UserService();
            ProxyFactory proxyFactory = new ProxyFactory();
            proxyFactory.setTarget(userService);
            proxyFactory.addAdvice(new AfterReturningAdviceImpl());
            UserService proxy = (UserService) proxyFactory.getProxy();
            proxy.test();
        }
    }
    

Spring AOP:理解动态代理和 Advice_第3张图片

  1. ThrowsAdvice:方法抛出异常后执行

    public class ThrowsAdviceImpl implements ThrowsAdvice {
    
        public void afterThrowing(Method method, Object[] args, Object target, RuntimeException ex) {
            System.out.println("方法抛出异常后执行");
        }
    }
    
    public class UserService {
    
        public void test(){
            System.out.println("test...");
            throw new RuntimeException();
        }
    }
    
    public class Demo {
    
        public static void main(String[] args) {
            UserService userService = new UserService();
            ProxyFactory proxyFactory = new ProxyFactory();
            proxyFactory.setTarget(userService);
            proxyFactory.addAdvice(new ThrowsAdviceImpl());
            UserService proxy = (UserService) proxyFactory.getProxy();
            proxy.test();
        }
    }
    

Spring AOP:理解动态代理和 Advice_第4张图片

ThrowsAdvice这个接口上没有任何方法,因为方法是由反射调用的.我们定义可以自己定义方法afterThrowing,只需要在参数里面加入异常参数就可以了,只要代码中抛出我们指定的异常就会执行afterThrowing方法.如果不是对应的异常将不会执行afterThrowing.

  1. AroundAdvice:功能最强大的Advice,可以自定义执行顺序

    public class AroundAdviceImpl implements MethodInterceptor {
    
        @Override
        public Object invoke(MethodInvocation invocation) throws Throwable {
            System.out.println("around before ...");
            Object proceed = invocation.proceed();
            System.out.println("around after ...");
            return proceed;
        }
    }
    
    public class Demo {
    
        public static void main(String[] args) {
            UserService userService = new UserService();
            ProxyFactory proxyFactory = new ProxyFactory();
            proxyFactory.setTarget(userService);
            proxyFactory.addAdvice(new AroundAdviceImpl());
            UserService proxy = (UserService) proxyFactory.getProxy();
            proxy.test();
        }
    }
    

Spring AOP:理解动态代理和 Advice_第5张图片

Advisor

跟Advice类似的还有一个Advisor的概念,一个Advisor是由一个Pointcut和一个Advice组成的,通过Pointcut可以指定要需要被代理的逻辑,比如一个UserSevice类中有两个方法,按上面的例子,这两个方法都会被代理,被增强,那么我们现在可以通过Advisor,来控制到具体代理哪一个方法,比如:

public class UserService {

    public void test(){
        System.out.println("test...");
    }

    public void test1(){
        System.out.println("test1...");
    }
}

public class Demo {

    public static void main(String[] args) {
        UserService userService = new UserService();
        ProxyFactory proxyFactory = new ProxyFactory();
        proxyFactory.setTarget(userService);
        proxyFactory.addAdvisor(new PointcutAdvisor() {
            @Override
            public Pointcut getPointcut() {
                return new StaticMethodMatcherPointcut() {
                    @Override
                    public boolean matches(Method method, Class<?> targetClass) {
                        // 只代理test方法
                        return method.getName().equals("test");
                    }
                };
            }

            @Override
            public Advice getAdvice() {
                return (MethodInterceptor) invocation -> {
                    System.out.println("before....");
                    Object res = invocation.proceed();
                    System.out.println("after....");
                    return res;
                };
            }

            @Override
            public boolean isPerInstance() {
                return false;
            }
        });

        UserService proxy = (UserService) proxyFactory.getProxy();
        proxy.test();
        proxy.test1();
    }
}

Spring AOP:理解动态代理和 Advice_第6张图片

上面示例代码表示,产生的代理对象,只有在执行test方法时才会被增强,会执行额外的逻辑,而在执行其他方法时是不会增强的.

创建代理对象的方式

上面介绍了Spring中提供了ProxyFactory,Advisor,Advice,PointCut等技术来实现代理对象的创建,但是我们在使用Spring时,我们并不会直接这么去使用ProxyFactory,比如说,我们希望ProxyFactory所产生的代理对象能直接就是Bean,能直接从Spring容器中得到UserService的代理对象,而这些Spring都是支持的,只不过,作为开发者的我们肯定得告诉Spring,那些类需要被代理,代理逻辑是什么

ProxyFactoryBean

@Bean
public ProxyFactoryBean factoryBean() {
    UserService userService = new UserService();
    ProxyFactoryBean proxyFactoryBean = new ProxyFactoryBean();
    proxyFactoryBean.setTarget(userService);
    proxyFactoryBean.addAdvice((MethodInterceptor) invocation -> {
        System.out.println("before...");
        Object res = invocation.proceed();
        System.out.println("after...");
        return res;
    });
    return proxyFactoryBean;
}

通过这种方法定义一个UserService的Bean,并且是经过了AOP的,但是这种方式只能针对某一个Bean,它是一个FactoryBean,所以利用了FactoryBean技术,简介的将UserService的代理对象作为了Bean.

ProxyFactoryBean还有额外的功能,比如可以把某个Advice或Advisor定义为Bean,然后再ProxyFactoryBean中进行设置.

@Bean
public MethodInterceptor methodInterceptor() {
    return invocation -> {
        System.out.println("before...");
        Object res = invocation.proceed();
        System.out.println("after...");
        return res;
    };
}

@Bean
public ProxyFactoryBean factoryBean() {
    UserService userService = new UserService();
    ProxyFactoryBean proxyFactoryBean = new ProxyFactoryBean();
    proxyFactoryBean.setTarget(userService);
    proxyFactoryBean.setInterceptorNames("methodInterceptor");
    return proxyFactoryBean;
}

BeanNameAutoProxyCreator

@Bean
public MethodInterceptor methodInterceptor() {
    return invocation -> {
        System.out.println("before...");
        Object res = invocation.proceed();
        System.out.println("after...");
        return res;
    };
}

@Bean
public BeanNameAutoProxyCreator beanNameAutoProxyCreator(){
    BeanNameAutoProxyCreator beanNameAutoProxyCreator = new BeanNameAutoProxyCreator();
    beanNameAutoProxyCreator.setBeanNames("user*");
    beanNameAutoProxyCreator.setInterceptorNames("methodInterceptor");
    beanNameAutoProxyCreator.setProxyTargetClass(true);
    return beanNameAutoProxyCreator;
}

通过BeanNameAutoProxyCreator可以对批量的Bean进行AOP,并且指定了代理逻辑,制定了一个interceptorName,也就是一个Advice,前提条件是这个Advice也得是一个Bean,这样Spring才能找到的,但是BeanNameAutoProxyCreator的缺点也很明显,他只能根据beanName来指定想要代理的bean.

DefaultAdvisorAutoProxyCreator

@Bean
public DefaultPointcutAdvisor defaultPointcutAdvisor(){
    NameMatchMethodPointcut pointcut = new NameMatchMethodPointcut();
    pointcut.addMethodName("test");

    DefaultPointcutAdvisor res = new DefaultPointcutAdvisor();
    res.setPointcut(pointcut);
    res.setAdvice(new AroundAdviceImpl());
    return res;
}

@Bean
public DefaultAdvisorAutoProxyCreator defaultAdvisorAutoProxyCreator(){
    return new DefaultAdvisorAutoProxyCreator();
}

通过DefaultAdvisorAutoProxyCreator会直接去找所有Advisor类型的Bean,根据Advisor中PointCut和Advice信息,确定要代理的Bean以及代理逻辑.

注解

@Component
@Aspect
public class Advice {

    @Before("execution(public void com.fanqiechaodan.service.UserService.test())")
    public void before(JoinPoint joinPoint){
        System.out.println("before........");
    }
}

通过上面这个类,我们直接定义好了所要代理的方法(通过一个表达式),以及代理逻辑(被@Before修饰的方法),简单明了,这样对于Spring来说,它要做的就是来解析这些注解了,解析之后得到对应的Pointcut对象,Advice对象,生成Advisor对象,扔进ProxyFactory中,进而产生对应的代理对象.

Advice在Spring AOP中对应的API

上面说到的Aspject中的注解,其中有五个是用来定义Advice的,表示代理逻辑,以及执行时机:

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

Spring自己也提供了类似的执行实际的实现类:

  1. 接口MethodBeforeAdvice,继承了接口BeforeAdvice
  2. 接口AfterReturningAdvice
  3. 接口ThrowsAdvice
  4. 接口AfterAdvice
  5. 接口MethodInterceptor

Spring会把五个注解解析为对应的Advice类:

  1. @Before:AspectJMethodBeforeAdvice,实际上就是一个MethodBeforeAdvice
  2. @AfterReturning:AspectJAfterReturningAdvice,实际上就是一个AfterReturningAdvice
  3. @AfterThrowing:AspectJAfterThrowingAdvice,实际上就是一个MethodInterceptor
  4. @After:AspectJAfterAdvice,实际上就是一个MethodInterceptor
  5. @Around:AspectJAroundAdvice,实际上就是一个MethodInterceptor

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