springAOP通知

1.什么是AOP通知

AOP通知就是面向切面编程中冗余的代码。
比如在每次对数据库进行操作之前，需要记录操作的SQL语句，或者调用方法前打印方法名，这些就是AOP的通知。
用大白话说，就是在横向业务中相同的操作，比如日志，事物，异常等等。

2.通知的类型

1.环绕通知
1.1 jdk代理
1.2 cglib代理
2.前置通知
3.后置通知
4.异常通知
5.引介通知

3.原理

ProxyFactoryBean是FactoryBean接口的实现类，FactoryBean负责实例化一个Bean，而ProxyFactoryBean负责为其他Bean创建代理实例。在spring中，使用ProxyFactoryBean是创建AOP代理的基本方式。

4.例子

4.1创建一个spring项目

springAOP通知_springAOP通知

4.2创建Java文件

springAOP通知_实现自定义AOP_02

package aspect;

import java.lang.reflect.Method;

import org.springframework.aop.AfterReturningAdvice;

public class AfterAspect implements AfterReturningAdvice{

   @Override
   public void afterReturning(Object returnValue, Method method,
         Object[] args, Object target) throws Throwable {
      
      System.out.println("AfterAspect#afterReturning");
      
   }

}
package aspect;

import java.lang.reflect.Method;

import org.springframework.aop.MethodBeforeAdvice;

public class BeforeAspect implements MethodBeforeAdvice{

   @Override
   public void before(Method method, Object[] args, Object target)
         throws Throwable {
      
      System.out.println("BeforeAspect#before");
      
   }

}
package aspect;

import intf.PswdDao;

import org.aopalliance.intercept.MethodInvocation;
import org.springframework.aop.IntroductionInterceptor;

public class IntroductionAspect implements IntroductionInterceptor , PswdDao{

   @Override
   public Object invoke(MethodInvocation invocation) throws Throwable {
      if(implementsInterface(invocation.getMethod().getDeclaringClass())){
         return invocation.getMethod().invoke(this, invocation);
      } else {
         return invocation.proceed();
      }
   }

   @Override
   public boolean implementsInterface(Class<?> intf) {
      return intf.isAssignableFrom(PswdDao.class);
   }

   @Override
   public void sayPswd() {
      System.out.println("Aspect#sayPswd");
   }


}
package aspect;

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

public class MyAspect implements MethodInterceptor{

   @Override
   public Object invoke(MethodInvocation arg0) throws Throwable {
      before();
      Object object = arg0.proceed();
      after();
      return object;
   }


   private void before(){
      System.out.println("before");
   }
   
   private void after(){
      System.out.println("after");
   }
   
}
package bean;

public class People {

   public void say(){
      System.out.println("People#say");
   }
   
}
package client;

import intf.PswdDao;
import intf.UserDao;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import bean.People;

public class Main {

   public static void main(String[] args) {
      
      ApplicationContext applicationContext = new ClassPathXmlApplicationContext(
            "resource/*.xml");
      UserDao userDao = (UserDao)applicationContext.getBean("userDaoInterceptorProxy");
      userDao.add();
      userDao.modify();
      System.out.println();
      People people = (People)applicationContext.getBean("peopleInterceptorProxy");
      people.say();
      System.out.println();
      userDao = (UserDao)applicationContext.getBean("userDaoBeforeProxy");
      userDao.add();
      userDao.modify();
      System.out.println();
      userDao = (UserDao)applicationContext.getBean("userDaoAfterProxy");
      userDao.add();
      userDao.modify();
      System.out.println();
      userDao = (UserDao) applicationContext.getBean("pswdDaoInterceptorProxy");
      userDao.add();
      userDao.modify();
      ((PswdDao) userDao).sayPswd();
   }

}
package impl;

import intf.UserDao;

public class UserDaoImpl implements UserDao{

   @Override
   public void add() {
      System.out.println("UserDaoImpl#add");
   }

   @Override
   public void modify() {
      System.out.println("UserDaoImpl#modify");
   }

}
package intf;

public interface PswdDao {

   void sayPswd();
   
}
package intf;

public interface UserDao {

   void add();
   
   void modify();
   
}

4.3创建xml文件

bean.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"
   xsi:schemaLocation="http://www.springframework.org/schema/beans 
   http://www.springframework.org/schema/beans/spring-beans.xsd">
   <!-- 目标类 -->
   <bean id="userDao" class="impl.UserDaoImpl"></bean>
   <!-- 增强类 -->
   <bean id="aspect" class="aspect.MyAspect"></bean>
   <!-- 代理对象 -->
   <bean id="userDaoInterceptorProxy" class="org.springframework.aop.framework.ProxyFactoryBean">
      <!-- 增强的接口 -->
      <property name="proxyInterfaces">
         <value>intf.UserDao</value>
      </property>
      <!-- 指定目标对象 -->
      <property name="target" ref="userDao">
      </property>
      <!-- 指定增强类 -->
      <property name="interceptorNames"> 
         <value>aspect</value>
      </property>
      <property name="proxyTargetClass">
         <value>false</value>
      </property>
   </bean>
   <bean id="people" class="bean.People"></bean>
   <bean id="peopleInterceptorProxy" class="org.springframework.aop.framework.ProxyFactoryBean">
      <!-- 指定目标对象 -->
      <property name="target" ref="people">
      </property>
      <!-- 指定增强类 -->
      <property name="interceptorNames"> 
         <value>aspect</value>
      </property>
      <property name="proxyTargetClass">
         <value>true</value>
      </property>
   </bean>
   <bean id="userDaoBeforeProxy" class="org.springframework.aop.framework.ProxyFactoryBean">
      <!-- 增强的接口 -->
      <property name="proxyInterfaces">
         <value>intf.UserDao</value>
      </property>
      <!-- 指定目标对象 -->
      <property name="target" ref="userDao">
      </property>
      <!-- 指定增强类 -->
      <property name="interceptorNames"> 
         <value>beforeAspect</value>
      </property>
      <property name="proxyTargetClass">
         <value>false</value>
      </property>
   </bean>
   <!-- 增强类 -->
   <bean id="beforeAspect" class="aspect.BeforeAspect"></bean>
   <!-- 增强类 -->
   <bean id="afterAspect" class="aspect.AfterAspect"></bean>
   <bean id="userDaoAfterProxy" class="org.springframework.aop.framework.ProxyFactoryBean">
      <!-- 增强的接口 -->
      <property name="proxyInterfaces">
         <value>intf.UserDao</value>
      </property>
      <!-- 指定目标对象 -->
      <property name="target" ref="userDao">
      </property>
      <!-- 指定增强类 -->
      <property name="interceptorNames"> 
         <value>afterAspect</value>
      </property>
      <property name="proxyTargetClass">
         <value>false</value>
      </property>
   </bean>
   <bean id="intriductionAspect" class="aspect.IntroductionAspect"></bean>
   <bean id="pswdDaoInterceptorProxy" class="org.springframework.aop.framework.ProxyFactoryBean">
      <!-- 增强的接口 -->
      <property name="proxyInterfaces">
         <value>intf.PswdDao</value>
      </property>
      <!-- 指定目标对象 -->
      <property name="target" ref="intriductionAspect">
      </property>
      <!-- 指定增强类 -->
      <property name="interceptorNames"> 
         <value>intriductionAspect</value>
      </property>
      <property name="proxyTargetClass">
         <value>false</value>
      </property>
   </bean>
</beans>

4.4运行结果

before
UserDaoImpl#add
after
before
UserDaoImpl#modify
after

before
People#say
after

BeforeAspect#before
UserDaoImpl#add
BeforeAspect#before
UserDaoImpl#modify

UserDaoImpl#add
AfterAspect#afterReturning
UserDaoImpl#modify
AfterAspect#afterReturning

Exception in thread "main" java.lang.ClassCastException: com.sun.proxy.$Proxy5 cannot be cast to intf.UserDao
   at client.Main.main(Main.java:32)

5.总结

spring的通知类型：
1.环绕通知
1.1 jdk代理
1.2 cglib代理
2.前置通知
3.后置通知
4.异常通知
5.引介通知