SpringAOP模拟实现

duration～2024-11-22 16:50

文章目录

1_底层切点、通知、切面

注意点：

  1. 底层的切点实现
  2. 底层的通知实现
  3. 底层的切面实现
  4. ProxyFactory 用来创建代理
    • 如果指定了接口，且 proxyTargetClass = false，使用 JdkDynamicAopProxy
    • 如果没有指定接口，或者 proxyTargetClass = true，使用 ObjenesisCglibAopProxy
    • 例外：如果目标是接口类型或已经是 jdk 代理，使用 JdkDynamicAopProxy
java 复制代码 
public class A15 {
    public static void main(String[] args) {
        /*
            两个切面概念
            aspect =
                通知1(advice) +  切点1(pointcut)
                通知2(advice) +  切点2(pointcut)
                通知3(advice) +  切点3(pointcut)
                ...
            advisor = 更细粒度的切面，包含一个通知和切点
         */

        // 1. 备好切点
        AspectJExpressionPointcut pointcut = new AspectJExpressionPointcut();
        pointcut.setExpression("execution(* foo())");
        // 2. 备好通知
        MethodInterceptor advice = invocation -> {
            System.out.println("before...");
            Object result = invocation.proceed(); // 调用目标
            System.out.println("after...");
            return result;
        };
        // 3. 备好切面
        DefaultPointcutAdvisor advisor = new DefaultPointcutAdvisor(pointcut, advice);

        /*
           4. 创建代理
                a. proxyTargetClass = false, 目标实现了接口, 用 jdk 实现
                b. proxyTargetClass = false,  目标没有实现接口, 用 cglib 实现
                c. proxyTargetClass = true, 总是使用 cglib 实现
         */
        Target2 target = new Target2();
        ProxyFactory factory = new ProxyFactory();
        factory.setTarget(target);
        factory.addAdvisor(advisor);
        factory.setInterfaces(target.getClass().getInterfaces());
        factory.setProxyTargetClass(false);
        Target2 proxy = (Target2) factory.getProxy();
        System.out.println(proxy.getClass());
        proxy.foo();
        proxy.bar();
        /*
            学到了什么
                a. Spring 的代理选择规则
                b. 底层的切点实现
                c. 底层的通知实现
                d. ProxyFactory 是用来创建代理的核心实现, 用 AopProxyFactory 选择具体代理实现
                    - JdkDynamicAopProxy
                    - ObjenesisCglibAopProxy
         */
    }

    interface I1 {
        void foo();

        void bar();
    }

    static class Target1 implements I1 {
        public void foo() {
            System.out.println("target1 foo");
        }

        public void bar() {
            System.out.println("target1 bar");
        }
    }

    static class Target2 {
        public void foo() {
            System.out.println("target2 foo");
        }

        public void bar() {
            System.out.println("target2 bar");
        }
    }
}

2_切点匹配

切点匹配：

  1. 常见 aspectj 切点用法
  2. aspectj 切点的局限性，实际的 @Transactional 切点实现
java 复制代码 
import org.springframework.aop.aspectj.AspectJExpressionPointcut;
import org.springframework.aop.support.StaticMethodMatcherPointcut;
import org.springframework.core.annotation.MergedAnnotations;
import org.springframework.transaction.annotation.Transactional;

import java.lang.reflect.Method;

public class A16 {
    public static void main(String[] args) throws NoSuchMethodException {
//        AspectJExpressionPointcut pt1 = new AspectJExpressionPointcut();
//        pt1.setExpression("execution(* bar())");
//        System.out.println(pt1.matches(T1.class.getMethod("foo"), T1.class));
//        System.out.println(pt1.matches(T1.class.getMethod("bar"), T1.class));
//
//        AspectJExpressionPointcut pt2 = new AspectJExpressionPointcut();
//        pt2.setExpression("@annotation(org.springframework.transaction.annotation.Transactional)");
//        System.out.println(pt2.matches(T1.class.getMethod("foo"), T1.class));
//        System.out.println(pt2.matches(T1.class.getMethod("bar"), T1.class));

        StaticMethodMatcherPointcut pt3 = new StaticMethodMatcherPointcut() {
            @Override
            public boolean matches(Method method, Class<?> targetClass) {
                // 检查方法上是否加了 Transactional 注解
                MergedAnnotations annotations = MergedAnnotations.from(method);
                if (annotations.isPresent(Transactional.class)) {
                    return true;
                }
                // 查看类上是否加了 Transactional 注解
                annotations = MergedAnnotations.from(targetClass, MergedAnnotations.SearchStrategy.TYPE_HIERARCHY);
                if (annotations.isPresent(Transactional.class)) {
                    return true;
                }
                return false;
            }
        };

        System.out.println(pt3.matches(T1.class.getMethod("foo"), T1.class));
        System.out.println(pt3.matches(T1.class.getMethod("bar"), T1.class));
        System.out.println(pt3.matches(T2.class.getMethod("foo"), T2.class));
        System.out.println(pt3.matches(T3.class.getMethod("foo"), T3.class));

        /*
            学到了什么
                a. 底层切点实现是如何匹配的: 调用了 aspectj 的匹配方法
                b. 比较关键的是它实现了 MethodMatcher 接口, 用来执行方法的匹配
         */
    }


    static class T1 {
        @Transactional
        public void foo() {
        }
        public void bar() {
        }
    }

    @Transactional
    static class T2 {
        public void foo() {
        }
    }

    @Transactional
    interface I3 {
        void foo();
    }
    static class T3 implements I3 {
        public void foo() {
        }
    }
}

3_从 @Aspect 到 Advisor

1_代理创建器

注意点：

  1. AnnotationAwareAspectJAutoProxyCreator 的作用
    • 将高级 @Aspect 切面统一为低级 Advisor 切面。
    • 在合适的时机创建代理。
  2. findEligibleAdvisors 找到有【资格】的 Advisors
    • 有【资格】的 Advisor 一部分是低级的, 可以由自己编写, 如本例 A17 中的 advisor3。
    • 有【资格】的 Advisor 另一部分是高级的, 由解析 @Aspect 后获得。
  3. wrapIfNecessary
    • 它内部调用 findEligibleAdvisors, 只要返回集合不空, 则表示需要创建代理。
    • 它的调用时机通常在原始对象初始化后执行, 但碰到循环依赖会提前至依赖注入之前执行。
java 复制代码 
package org.springframework.aop.framework.autoproxy;


import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;
import org.aspectj.lang.annotation.After;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.springframework.aop.Advisor;
import org.springframework.aop.aspectj.AspectJExpressionPointcut;
import org.springframework.aop.aspectj.annotation.AnnotationAwareAspectJAutoProxyCreator;
import org.springframework.aop.support.DefaultPointcutAdvisor;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.ConfigurationClassPostProcessor;
import org.springframework.context.support.GenericApplicationContext;
import org.springframework.transaction.annotation.Transactional;

import java.util.List;

/**
 * @author shenyang
 * @version 1.0
 * @info TestAop
 * @since 2024/8/17 20:26
 */
public class A17 {

    @Aspect//高级切面
    static class Aspect1{
        @Before("execution(* foo())")
        public void before(){
            System.out.println("aspect1 before.....");
        }
        @After("execution(* foo())")
        public void after(){
            System.out.println("aspect1 after.....");
        }
    }

    @Configuration
    static class Config {
        @Bean//低级切面
        public Advisor advisor3(MethodInterceptor advice3) {
            AspectJExpressionPointcut pointcut = new AspectJExpressionPointcut();
            pointcut.setExpression("execution(* foo())");
            return new DefaultPointcutAdvisor(pointcut, advice3);
        }
        @Bean
        public MethodInterceptor advice3(){
            return new MethodInterceptor() {
                @Override
                public Object invoke(MethodInvocation methodInvocation) throws Throwable {
                    System.out.println("advice3 before.....");
                    Object proceed = methodInvocation.proceed();
                    System.out.println("advice3 after.....");
                    return proceed;
                }
            };
        }
    }

    static class T1 {
        public void foo() {
            System.out.println("target1 foo");
        }
    }

    static class T2 {
        public void bar() {
            System.out.println("target2 bar");
        }
    }

    public static void main(String[] args) {
        GenericApplicationContext context = new GenericApplicationContext();
        context.registerBean("aspect1",Aspect1.class);
        context.registerBean("config",Config.class);
        context.registerBean(ConfigurationClassPostProcessor.class);
        context.registerBean(AnnotationAwareAspectJAutoProxyCreator.class);
        context.refresh();
        AnnotationAwareAspectJAutoProxyCreator creator = context.getBean(AnnotationAwareAspectJAutoProxyCreator.class);
        List<Advisor> advisors = creator.findEligibleAdvisors(T2.class, "target2");
        System.out.println("====================");
//        advisors.forEach(System.out::println);
        T1 o1 = (T1) creator.wrapIfNecessary(new T1(), "target1", "target1");
        T2 o2 = (T2) creator.wrapIfNecessary(new T2(), "target2", "target2");
        System.out.println(o1.getClass()+" "+o2.getClass());
        o1.foo();
        o2.bar();
    }

}

2_代理创建时机

注意点：

  1. 代理的创建时机
    • 初始化之后 (无循环依赖时)
    • 实例创建后, 依赖注入前 (有循环依赖时), 并暂存于二级缓存。
  2. 依赖注入与初始化不应该被增强, 仍应被施加于原始对象
java 复制代码 
package org.springframework.aop.framework.autoproxy;

import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;
import org.springframework.aop.Advisor;
import org.springframework.aop.aspectj.AspectJExpressionPointcut;
import org.springframework.aop.aspectj.annotation.AnnotationAwareAspectJAutoProxyCreator;
import org.springframework.aop.support.DefaultPointcutAdvisor;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.CommonAnnotationBeanPostProcessor;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.ConfigurationClassPostProcessor;
import org.springframework.context.support.GenericApplicationContext;

import javax.annotation.PostConstruct;

public class A17_1 {

    public static void main(String[] args) {
        GenericApplicationContext context = new GenericApplicationContext();
        context.registerBean(ConfigurationClassPostProcessor.class);
        context.registerBean(Config.class);
        context.refresh();
        context.close();
        // 创建 -> (*) 依赖注入 -> 初始化 (*)
        /*
            学到了什么
                a. 代理的创建时机
                    1. 初始化之后 (无循环依赖时)
                    2. 实例创建后, 依赖注入前 (有循环依赖时), 并暂存于二级缓存
                b. 依赖注入与初始化不应该被增强, 仍应被施加于原始对象
         */
    }

    @Configuration
    static class Config {
        @Bean // 解析 @Aspect、产生代理
        public AnnotationAwareAspectJAutoProxyCreator annotationAwareAspectJAutoProxyCreator() {
            return new AnnotationAwareAspectJAutoProxyCreator();
        }

        @Bean // 解析 @Autowired
        public AutowiredAnnotationBeanPostProcessor autowiredAnnotationBeanPostProcessor() {
            return new AutowiredAnnotationBeanPostProcessor();
        }

        @Bean // 解析 @PostConstruct
        public CommonAnnotationBeanPostProcessor commonAnnotationBeanPostProcessor() {
            return new CommonAnnotationBeanPostProcessor();
        }

        @Bean
        public Advisor advisor(MethodInterceptor advice) {
            AspectJExpressionPointcut pointcut = new AspectJExpressionPointcut();
            pointcut.setExpression("execution(* foo())");
            return new DefaultPointcutAdvisor(pointcut, advice);
        }

        @Bean
        public MethodInterceptor advice() {
            return (MethodInvocation invocation) -> {
                System.out.println("before...");
                return invocation.proceed();
            };
        }

        @Bean
        public Bean1 bean1() {
            return new Bean1();
        }

        @Bean
        public Bean2 bean2() {
            return new Bean2();
        }
    }

    static class Bean1 {
        public void foo() {

        }
        public Bean1() {
            System.out.println("Bean1()");
        }
        @Autowired public void setBean2(Bean2 bean2) {
            System.out.println("Bean1 setBean2(bean2) class is: " + bean2.getClass());
        }
        @PostConstruct public void init() {
            System.out.println("Bean1 init()");
        }
    }

    static class Bean2 {
        public Bean2() {
            System.out.println("Bean2()");
        }
        @Autowired public void setBean1(Bean1 bean1) {
            System.out.println("Bean2 setBean1(bean1) class is: " + bean1.getClass());
        }
        @PostConstruct public void init() {
            System.out.println("Bean2 init()");
        }
    }
}

3_@Before 对应的低级通知

注意点：

  1. @Before 前置通知会被转换为原始的 AspectJMethodBeforeAdvice 形式, 该对象包含了如下信息
    • 通知代码从哪儿来
    • 切点是什么(这里为啥要切点, 后面解释)
    • 通知对象如何创建, 本例共用同一个 Aspect 对象
  2. 类似的还有
    • AspectJAroundAdvice (环绕通知)
    • AspectJAfterReturningAdvice
    • AspectJAfterThrowingAdvice (环绕通知)
    • AspectJAfterAdvice (环绕通知)
java 复制代码 
package org.springframework.aop.framework.autoproxy;

import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Before;
import org.springframework.aop.Advisor;
import org.springframework.aop.aspectj.AspectInstanceFactory;
import org.springframework.aop.aspectj.AspectJExpressionPointcut;
import org.springframework.aop.aspectj.AspectJMethodBeforeAdvice;
import org.springframework.aop.aspectj.SingletonAspectInstanceFactory;
import org.springframework.aop.support.DefaultPointcutAdvisor;

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

public class A17_2 {

    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");
        }

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

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

        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());
        // 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);
            }
        }
        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(这里为啥要切点, 后面解释)
                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
                4. AspectJAfterAdvice (环绕通知)
         */

    }
}

4_静态通知调用

代理对象调用流程如下（以 JDK 动态代理实现为例）

  • 从 ProxyFactory 获得 Target 和环绕通知链，根据他俩创建 MethodInvocation，简称 mi
  • 首次执行 mi.proceed() 发现有下一个环绕通知，调用它的 invoke(mi)
  • 进入环绕通知1，执行前增强，再次调用 mi.proceed() 发现有下一个环绕通知，调用它的 invoke(mi)
  • 进入环绕通知2，执行前增强，调用 mi.proceed() 发现没有环绕通知，调用 mi.invokeJoinPoint() 执行目标方法
  • 目标方法执行结束，将结果返回给环绕通知2，执行环绕通知2 的后增强
  • 环绕通知2继续将结果返回给环绕通知1，执行环绕通知1 的后增强
  • 环绕通知1返回最终的结果

图中不同颜色对应一次环绕通知或目标的调用起始至终结
Proxy InvocationHandler MethodInvocation ProxyFactory MethodInterceptor1 MethodInterceptor2 Target invoke() 获得 Target 获得 MethodInterceptor 链 创建 mi mi.proceed() invoke(mi) 前增强 mi.proceed() invoke(mi) 前增强 mi.proceed() mi.invokeJoinPoint() 结果 后增强 结果 后增强 结果 Proxy InvocationHandler MethodInvocation ProxyFactory MethodInterceptor1 MethodInterceptor2 Target

1_通知调用过程

代理方法执行时会做如下工作：

  1. 通过 proxyFactory 的 getInterceptorsAndDynamicInterceptionAdvice() 将其他通知统一转换为 MethodInterceptor 环绕通知
    • MethodBeforeAdviceAdapter 将 @Before AspectJMethodBeforeAdvice 适配为 MethodBeforeAdviceInterceptor
    • AfterReturningAdviceAdapter 将 @AfterReturning AspectJAfterReturningAdvice 适配为 AfterReturningAdviceInterceptor
    • 这体现的是适配器设计模式
  2. 所谓静态通知，体现在上面方法的 Interceptors 部分，这些通知调用时无需再次检查切点，直接调用即可
  3. 结合目标与环绕通知链，创建 MethodInvocation 对象，通过它完成整个调用
java 复制代码 
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.framework.ProxyFactory;
import org.springframework.aop.framework.ReflectiveMethodInvocation;
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();
        ProxyFactory proxyFactory = new ProxyFactory();
        proxyFactory.setTarget(target);
        proxyFactory.addAdvice(ExposeInvocationInterceptor.INSTANCE); // 准备把 MethodInvocation 放入当前线程
        proxyFactory.addAdvisors(list);

        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>");
        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 (环绕通知s + 目标)
        MethodInvocation methodInvocation = new ReflectiveMethodInvocation(
                null, target, Target.class.getMethod("foo"), new Object[0], Target.class, methodInterceptorList
        );
        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
         */

    }
}

2_模拟 MethodInvocation

注意点：

  1. proceed() 方法调用链中下一个环绕通知
  2. 每个环绕通知内部继续调用 proceed()
  3. 调用到没有更多通知了, 就调用目标方法

MethodInvocation 的编程技巧在实现拦截器、过滤器时能用上

java 复制代码 
package org.springframework.aop.framework;

import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;

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

/*
    模拟调用链过程, 是一个简单的递归过程
        1. proceed() 方法调用链中下一个环绕通知
        2. 每个环绕通知内部继续调用 proceed()
        3. 调用到没有更多通知了, 就调用目标方法
 */
public class A18_1 {

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

    static class Advice1 implements MethodInterceptor {
        public Object invoke(MethodInvocation invocation) throws Throwable {
            System.out.println("Advice1.before()");
            Object result = invocation.proceed();// 调用下一个通知或目标
            System.out.println("Advice1.after()");
            return result;
        }
    }

    static class Advice2 implements MethodInterceptor {
        public Object invoke(MethodInvocation invocation) throws Throwable {
            System.out.println("Advice2.before()");
            Object result = invocation.proceed();// 调用下一个通知或目标
            System.out.println("Advice2.after()");
            return result;
        }
    }


    static class MyInvocation implements MethodInvocation {
        private Object target;  // 1
        private Method method;
        private Object[] args;
        List<MethodInterceptor> methodInterceptorList; // 2
        private int count = 1; // 调用次数

        public MyInvocation(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
        public Object proceed() throws Throwable { // 调用每一个环绕通知, 调用目标
            if (count > methodInterceptorList.size()) {
                // 调用目标， 返回并结束递归
                return method.invoke(target, args);
            }
            // 逐一调用通知, count + 1
            MethodInterceptor methodInterceptor = methodInterceptorList.get(count++ - 1);
            return methodInterceptor.invoke(this);
        }

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

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

    public static void main(String[] args) throws Throwable {
        Target target = new Target();
        List<MethodInterceptor> list = new ArrayList<>();

        list.add(new Advice1());
        list.add(new Advice2());
        MyInvocation invocation = new MyInvocation(target, Target.class.getMethod("foo"), new Object[0], list);
        invocation.proceed();
    }
}

5_动态通知调用

注意点：

  1. 通过 proxyFactory 的 getInterceptorsAndDynamicInterceptionAdvice() 将其他通知统一转换为 MethodInterceptor 环绕通知
  2. 所谓动态通知，体现在上面方法的 DynamicInterceptionAdvice 部分，这些通知调用时因为要为通知方法绑定参数，还需再次利用切点表达式
  3. 动态通知调用复杂程度高，性能较低
java 复制代码 
package org.springframework.aop.framework.autoproxy;

import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.springframework.aop.Advisor;
import org.springframework.aop.aspectj.annotation.AnnotationAwareAspectJAutoProxyCreator;
import org.springframework.aop.framework.ProxyFactory;
import org.springframework.aop.framework.ReflectiveMethodInvocation;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.ConfigurationClassPostProcessor;
import org.springframework.context.support.GenericApplicationContext;

import java.lang.reflect.Field;
import java.util.List;

public class A19 {

    @Aspect
    static class MyAspect {
        @Before("execution(* foo(..))") // 静态通知调用，不带参数绑定，执行时不需要切点
        public void before1() {
            System.out.println("before1");
        }

        @Before("execution(* foo(..)) && args(x)") // 动态通知调用，需要参数绑定，执行时还需要切点对象
        public void before2(int x) {
            System.out.printf("before2(%d)%n", x);
        }
    }

    static class Target {
        public void foo(int x) {
            System.out.printf("target foo(%d)%n", x);
        }
    }

    @Configuration
    static class MyConfig {
        @Bean
        AnnotationAwareAspectJAutoProxyCreator proxyCreator() {
            return new AnnotationAwareAspectJAutoProxyCreator();
        }

        @Bean
        public MyAspect myAspect() {
            return new MyAspect();
        }
    }

    public static void main(String[] args) throws Throwable {
        GenericApplicationContext context = new GenericApplicationContext();
        context.registerBean(ConfigurationClassPostProcessor.class);
        context.registerBean(MyConfig.class);
        context.refresh();

        AnnotationAwareAspectJAutoProxyCreator creator = context.getBean(AnnotationAwareAspectJAutoProxyCreator.class);
        List<Advisor> list = creator.findEligibleAdvisors(Target.class, "target");

        Target target = new Target();
        ProxyFactory factory = new ProxyFactory();
        factory.setTarget(target);
        factory.addAdvisors(list);
        Object proxy = factory.getProxy(); // 获取代理

        List<Object> interceptorList = factory.getInterceptorsAndDynamicInterceptionAdvice(Target.class.getMethod("foo", int.class), Target.class);
        for (Object o : interceptorList) {
            showDetail(o);
        }

        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>");
        ReflectiveMethodInvocation invocation = new ReflectiveMethodInvocation(
                proxy, target, Target.class.getMethod("foo", int.class), new Object[]{100}, Target.class, interceptorList
        ) {};

        invocation.proceed();

        /*
            学到了什么
                a. 有参数绑定的通知调用时还需要切点，对参数进行匹配及绑定
                b. 复杂程度高, 性能比无参数绑定的通知调用低
         */
    }

    public static void showDetail(Object o) {
        try {
            Class<?> clazz = Class.forName("org.springframework.aop.framework.InterceptorAndDynamicMethodMatcher");
            if (clazz.isInstance(o)) {
                Field methodMatcher = clazz.getDeclaredField("methodMatcher");
                methodMatcher.setAccessible(true);
                Field methodInterceptor = clazz.getDeclaredField("interceptor");
                methodInterceptor.setAccessible(true);
                System.out.println("环绕通知和切点：" + o);
                System.out.println("\t切点为：" + methodMatcher.get(o));
                System.out.println("\t通知为：" + methodInterceptor.get(o));
            } else {
                System.out.println("普通环绕通知：" + o);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

补充------ Advice 常见子接口：

增强类型 常见 Advice 子接口/子类 描述
前置通知 MethodBeforeAdvice 方法调用前执行
后置通知 AfterReturningAdvice 方法调用后且正常返回时执行
环绕通知 MethodInterceptor 方法调用前后都可增强，控制流程
异常通知 ThrowsAdvice 方法抛出异常时增强
引介通知 DelegatingIntroductionInterceptor 为目标对象动态添加接口实现
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