第十八讲-通知调用(责任链模式)

第十八讲 通知调用(责任链模式)

AOP有各种通知类型，但是最终都要统一转为环绕通知执行，我们首先看一下代码中的图：

package org.springframework.aop.framework;

import org.aopalliance.intercept.MethodInvocation;
import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.AfterReturning;
import org.aspectj.lang.annotation.AfterThrowing;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Before;
import org.springframework.aop.Advisor;
import org.springframework.aop.aspectj.*;
import org.springframework.aop.interceptor.ExposeInvocationInterceptor;
import org.springframework.aop.support.DefaultPointcutAdvisor;

import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.List;

public class A18 {

    static class Aspect {
        @Before("execution(* foo())")
        public void before1() {
            System.out.println("before1");
        }

        @Before("execution(* foo())")
        public void before2() {
            System.out.println("before2");
        }

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

        @AfterReturning("execution(* foo())")
        public void afterReturning() {
            System.out.println("afterReturning");
        }

        @AfterThrowing("execution(* foo())")
        public void afterThrowing(Exception e) {
            System.out.println("afterThrowing " + e.getMessage());
        }

        @Around("execution(* foo())")
        public Object around(ProceedingJoinPoint pjp) throws Throwable {
            try {
                System.out.println("around...before");
                return pjp.proceed();
            } finally {
                System.out.println("around...after");
            }
        }
    }

    static class Target {
        public void foo() {
            System.out.println("target foo");
        }
    }

    @SuppressWarnings("all")
    public static void main(String[] args) throws Throwable {

        AspectInstanceFactory factory = new SingletonAspectInstanceFactory(new Aspect());
        // 1. 高级切面转低级切面类
        List<Advisor> list = new ArrayList<>();
        for (Method method : Aspect.class.getDeclaredMethods()) {
            if (method.isAnnotationPresent(Before.class)) {
                // 解析切点
                String expression = method.getAnnotation(Before.class).value();
                AspectJExpressionPointcut pointcut = new AspectJExpressionPointcut();
                pointcut.setExpression(expression);
                // 通知类
                AspectJMethodBeforeAdvice advice = new AspectJMethodBeforeAdvice(method, pointcut, factory);
                // 切面
                Advisor advisor = new DefaultPointcutAdvisor(pointcut, advice);
                list.add(advisor);
            } else if (method.isAnnotationPresent(AfterReturning.class)) {
                // 解析切点
                String expression = method.getAnnotation(AfterReturning.class).value();
                AspectJExpressionPointcut pointcut = new AspectJExpressionPointcut();
                pointcut.setExpression(expression);
                // 通知类
                AspectJAfterReturningAdvice advice = new AspectJAfterReturningAdvice(method, pointcut, factory);
                // 切面
                Advisor advisor = new DefaultPointcutAdvisor(pointcut, advice);
                list.add(advisor);
            } else if (method.isAnnotationPresent(Around.class)) {
                // 解析切点
                String expression = method.getAnnotation(Around.class).value();
                AspectJExpressionPointcut pointcut = new AspectJExpressionPointcut();
                pointcut.setExpression(expression);
                // 通知类
                AspectJAroundAdvice advice = new AspectJAroundAdvice(method, pointcut, factory);
                // 切面
                Advisor advisor = new DefaultPointcutAdvisor(pointcut, advice);
                list.add(advisor);
            }
        }
        for (Advisor advisor : list) {
            System.out.println(advisor);
        }

        /*
            @Before 前置通知会被转换为下面原始的 AspectJMethodBeforeAdvice 形式, 该对象包含了如下信息
                a. 通知代码从哪儿来
                b. 切点是什么
                c. 通知对象如何创建, 本例共用同一个 Aspect 对象
            类似的通知还有
                1. AspectJAroundAdvice (环绕通知)
                2. AspectJAfterReturningAdvice
                3. AspectJAfterThrowingAdvice (环绕通知)
                4. AspectJAfterAdvice (环绕通知)
         */

        // 2. 通知统一转换为环绕通知 MethodInterceptor
        /*

            其实无论 ProxyFactory 基于哪种方式创建代理, 最后干活(调用 advice)的是一个 MethodInvocation 对象
                a. 因为 advisor 有多个, 且一个套一个调用, 因此需要一个调用链对象, 即 MethodInvocation
                b. MethodInvocation 要知道 advice 有哪些, 还要知道目标, 调用次序如下

                将 MethodInvocation 放入当前线程
                    |-> before1 ----------------------------------- 从当前线程获取 MethodInvocation
                    |                                             |
                    |   |-> before2 --------------------          | 从当前线程获取 MethodInvocation
                    |   |                              |          |
                    |   |   |-> target ------ 目标   advice2    advice1
                    |   |                              |          |
                    |   |-> after2 ---------------------          |
                    |                                             |
                    |-> after1 ------------------------------------
                c. 从上图看出, 环绕通知才适合作为 advice, 因此其他 before、afterReturning 都会被转换成环绕通知
                d. 统一转换为环绕通知, 体现的是设计模式中的适配器模式
                    - 对外是为了方便使用要区分 before、afterReturning
                    - 对内统一都是环绕通知, 统一用 MethodInterceptor 表示

            此步获取所有执行时需要的 advice (静态)
                a. 即统一转换为 MethodInterceptor 环绕通知, 这体现在方法名中的 Interceptors 上
                b. 适配如下
                  - MethodBeforeAdviceAdapter 将 @Before AspectJMethodBeforeAdvice 适配为 MethodBeforeAdviceInterceptor
                  - AfterReturningAdviceAdapter 将 @AfterReturning AspectJAfterReturningAdvice 适配为 AfterReturningAdviceInterceptor
         */
        Target target = new Target();
        // 创建一个ProxyFactory对象
        ProxyFactory proxyFactory = new ProxyFactory();
        // 为target创建代理对象
        proxyFactory.setTarget(target);
        proxyFactory.addAdvice(ExposeInvocationInterceptor.INSTANCE); // 准备把 MethodInvocation 放入当前线程
        // 设置哪些低级的切面
        proxyFactory.addAdvisors(list);

        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>");
        // 将除了环绕通知的通知统一转为环绕通知，返回环绕通知集合
        List<Object> methodInterceptorList = proxyFactory.getInterceptorsAndDynamicInterceptionAdvice(Target.class.getMethod("foo"), Target.class);
        for (Object o : methodInterceptorList) {
            System.out.println(o);
        }

        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>");
        // 3. 创建并执行调用链 (所有的环绕通知 + 目标)
        MethodInvocation methodInvocation = new ReflectiveMethodInvocation(
                null, target, Target.class.getMethod("foo"), new Object[0], Target.class, methodInterceptorList
        );
        // 调用所有的环绕通知+目标
        methodInvocation.proceed();



        /*
            学到了什么
                a. 无参数绑定的通知如何被调用
                b. MethodInvocation 编程技巧: 拦截器、过滤器等等实现都与此类似
                c. 适配器模式在 Spring 中的体现
         */

    }
}

首先看如下的代码:

package org.springframework.aop.framework;

import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.AfterReturning;
import org.aspectj.lang.annotation.AfterThrowing;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Before;
import org.springframework.aop.Advisor;
import org.springframework.aop.aspectj.*;
import org.springframework.aop.support.DefaultPointcutAdvisor;

import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.List;

public class A18 {

    static class Aspect {
        @Before("execution(* foo())")
        public void before1() {
            System.out.println("before1");
        }

        @Before("execution(* foo())")
        public void before2() {
            System.out.println("before2");
        }

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

        @AfterReturning("execution(* foo())")
        public void afterReturning() {
            System.out.println("afterReturning");
        }

        @AfterThrowing("execution(* foo())")
        public void afterThrowing(Exception e) {
            System.out.println("afterThrowing " + e.getMessage());
        }

        @Around("execution(* foo())")
        public Object around(ProceedingJoinPoint pjp) throws Throwable {
            try {
                System.out.println("around...before");
                return pjp.proceed();
            } finally {
                System.out.println("around...after");
            }
        }
    }

    @SuppressWarnings("all")
    public static void main(String[] args) throws Throwable {

        AspectInstanceFactory factory = new SingletonAspectInstanceFactory(new Aspect());
        // 1. 高级切面转低级切面类
        List<Advisor> list = new ArrayList<>();
        for (Method method : Aspect.class.getDeclaredMethods()) {
            if (method.isAnnotationPresent(Before.class)) {
                // 解析切点
                String expression = method.getAnnotation(Before.class).value();
                AspectJExpressionPointcut pointcut = new AspectJExpressionPointcut();
                pointcut.setExpression(expression);
                // 通知类
                AspectJMethodBeforeAdvice advice = new AspectJMethodBeforeAdvice(method, pointcut, factory);
                // 切面
                Advisor advisor = new DefaultPointcutAdvisor(pointcut, advice);
                list.add(advisor);
            } else if (method.isAnnotationPresent(AfterReturning.class)) {
                // 解析切点
                String expression = method.getAnnotation(AfterReturning.class).value();
                AspectJExpressionPointcut pointcut = new AspectJExpressionPointcut();
                pointcut.setExpression(expression);
                // 通知类
                AspectJAfterReturningAdvice advice = new AspectJAfterReturningAdvice(method, pointcut, factory);
                // 切面
                Advisor advisor = new DefaultPointcutAdvisor(pointcut, advice);
                list.add(advisor);
            } else if (method.isAnnotationPresent(Around.class)) {
                // 解析切点
                String expression = method.getAnnotation(Around.class).value();
                AspectJExpressionPointcut pointcut = new AspectJExpressionPointcut();
                pointcut.setExpression(expression);
                // 通知类
                AspectJAroundAdvice advice = new AspectJAroundAdvice(method, pointcut, factory);
                // 切面
                Advisor advisor = new DefaultPointcutAdvisor(pointcut, advice);
                list.add(advisor);
            }
        }
        for (Advisor advisor : list) {
            System.out.println(advisor);
        }
    }
}

运行如下:

org.springframework.aop.support.DefaultPointcutAdvisor: pointcut [AspectJExpressionPointcut: () execution(* foo())]; advice [org.springframework.aop.aspectj.AspectJAroundAdvice: advice method [public java.lang.Object org.springframework.aop.framework.A18$Aspect.around(org.aspectj.lang.ProceedingJoinPoint) throws java.lang.Throwable]; aspect name '']
org.springframework.aop.support.DefaultPointcutAdvisor: pointcut [AspectJExpressionPointcut: () execution(* foo())]; advice [org.springframework.aop.aspectj.AspectJAfterReturningAdvice: advice method [public void org.springframework.aop.framework.A18$Aspect.afterReturning()]; aspect name '']
org.springframework.aop.support.DefaultPointcutAdvisor: pointcut [AspectJExpressionPointcut: () execution(* foo())]; advice [org.springframework.aop.aspectj.AspectJMethodBeforeAdvice: advice method [public void org.springframework.aop.framework.A18$Aspect.before1()]; aspect name '']
org.springframework.aop.support.DefaultPointcutAdvisor: pointcut [AspectJExpressionPointcut: () execution(* foo())]; advice [org.springframework.aop.aspectj.AspectJMethodBeforeAdvice: advice method [public void org.springframework.aop.framework.A18$Aspect.before2()]; aspect name '']

我们一共看到了四个通知。下面我们演示一下通知转换，代码就是第一部分的代码:

org.springframework.aop.support.DefaultPointcutAdvisor: pointcut [AspectJExpressionPointcut: () execution(* foo())]; advice [org.springframework.aop.aspectj.AspectJMethodBeforeAdvice: advice method [public void org.springframework.aop.framework.A18$Aspect.before1()]; aspect name '']
org.springframework.aop.support.DefaultPointcutAdvisor: pointcut [AspectJExpressionPointcut: () execution(* foo())]; advice [org.springframework.aop.aspectj.AspectJMethodBeforeAdvice: advice method [public void org.springframework.aop.framework.A18$Aspect.before2()]; aspect name '']
org.springframework.aop.support.DefaultPointcutAdvisor: pointcut [AspectJExpressionPointcut: () execution(* foo())]; advice [org.springframework.aop.aspectj.AspectJAroundAdvice: advice method [public java.lang.Object org.springframework.aop.framework.A18$Aspect.around(org.aspectj.lang.ProceedingJoinPoint) throws java.lang.Throwable]; aspect name '']
org.springframework.aop.support.DefaultPointcutAdvisor: pointcut [AspectJExpressionPointcut: () execution(* foo())]; advice [org.springframework.aop.aspectj.AspectJAfterReturningAdvice: advice method [public void org.springframework.aop.framework.A18$Aspect.afterReturning()]; aspect name '']
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
org.springframework.aop.interceptor.ExposeInvocationInterceptor@147ed70f
org.springframework.aop.framework.adapter.MethodBeforeAdviceInterceptor@61dd025
org.springframework.aop.framework.adapter.MethodBeforeAdviceInterceptor@124c278f
org.springframework.aop.aspectj.AspectJAroundAdvice: advice method [public java.lang.Object org.springframework.aop.framework.A18$Aspect.around(org.aspectj.lang.ProceedingJoinPoint) throws java.lang.Throwable]; aspect name ''
org.springframework.aop.framework.adapter.AfterReturningAdviceInterceptor@15b204a1
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
before1
before2
around...before
target foo
afterReturning
around...after

适配器模式

上述的普通通知转换融通自豪体现了一种设计模式，叫适配器模式

设配器模式体现的是将一套接口转为另一套接口，以便适合某种场景使用和调用，例如上面的普通通知在被调用时都会被转为环绕通知MethodInterceptor接口。

而中间做转换的类我们称之为适配器对象。从上面运行的控制套结果可以看出，

MethodBeforeAdviceAdapter 将 @Before AspectJMethodBeforeAdvices 适配为 MethodBeforeAdviceInterceptor

调用

在将普通的通知转为环绕通知之后接下来就是开始调用了。调用所有的环绕通知和目标， 那么是谁来做调用的事情呢？其实调用的工作是交给调用链来完成工作的。这个调用链的接口叫做MethodInvocation，

现在我们来模拟一下MethodInvocation的执行过程：

package org.springframework.aop.framework;

import org.aopalliance.intercept.Interceptor;
import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;
import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.AfterReturning;
import org.aspectj.lang.annotation.AfterThrowing;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Before;
import org.springframework.aop.Advisor;
import org.springframework.aop.aspectj.*;
import org.springframework.aop.interceptor.ExposeInvocationInterceptor;
import org.springframework.aop.support.DefaultPointcutAdvisor;

import java.lang.reflect.AccessibleObject;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.List;

public class A18_1 {
    static class Target{
        public void foo(){
            System.out.println("Target.foo()...");
        }
    }

    // 第一个通知类
    static class Advice1 implements MethodInterceptor {

        @Override
        public Object invoke(MethodInvocation invocation) throws Throwable {
            System.out.println("Advice1 before...");
            Object result = invocation.proceed();// 调用下一个通知或者目标
            System.out.println("Advice1 after...");
            return result;
        }
    }

    // 第二个通知类
    static class Advice2 implements MethodInterceptor {

        @Override
        public Object invoke(MethodInvocation invocation) throws Throwable {
            System.out.println("Advice2 before...");
            Object result = invocation.proceed();// 调用下一个通知或者目标
            System.out.println("Advice2 after...");
            return result;
        }
    }

    static class MyMethodInvocation implements MethodInvocation {

        // 准备一个目标
        private Object target;
        // 准备一个目标方法信息
        private Method method;
        // 准备方法执行时的参数
        private Object[] args;
        // 准备存储多个通知的集合
        private List<MethodInterceptor> methodInterceptorList;

        // 记录proceed的调用测试
        private int count = 1;

        public MyMethodInvocation(Object target, Method method, Object[] args, List<MethodInterceptor> methodInterceptorList) {
            this.target = target;
            this.method = method;
            this.args = args;
            this.methodInterceptorList = methodInterceptorList;
        }

        @Override
        public Method getMethod() {
            return method;
        }

        @Override
        public Object[] getArguments() {
            return args;
        }

        @Override // 调用每一个环绕通知，没有通知则调用目标
        public Object proceed() throws Throwable {
            if (count > methodInterceptorList.size()){
                // 调用目标, 返回并结束递归操作
                // 使用反射调用目标
                return method.invoke(target, args);
            }
            // 逐一调用通知,且count++
            /// 拿到第(count - 1)个环绕通知对象
            MethodInterceptor methodInterceptor = methodInterceptorList.get(count++ - 1);

            return methodInterceptor.invoke(this); // 递归调用
        }

        @Override
        public Object getThis() {
            return target;
        }

        @Override
        public AccessibleObject getStaticPart() {
            return method;
        }
    }

    // 编写一个测试类
    public static void main(String[] args) throws Throwable {
        Target target = new Target();
        // 准备两个通知
        List<MethodInterceptor> list = new ArrayList<>();
        list.add(new Advice1());
        list.add(new Advice2());
        // 准备调用链对象
        MyMethodInvocation myMethodInvocation = new MyMethodInvocation(target,Target.class.getDeclaredMethod("foo"),new Object[0], list);
        // 调用proceed方法
        myMethodInvocation.proceed();
    }
}

运行结果如下:

Advice1 before...
Advice2 before...
Target.foo()...
Advice2 after...
Advice1 after...

我们完美的实现了MethodInvocation调用链（责任链）工作:).

这种责任链模式不仅仅体现在环绕通知上，还体现在Tomcat中的过滤器，拦截器等等以及Spring框架等等。