AOP: Aspect Oriented Programing 面向切面编程

使用动态代理实现AOP

传统方法：

基于接口的动态代理：Proxy.newProxyInstance
基于子类的动态代理：Enhancer.create

术语：

JoinPoint（连接点）：所代理类的所有方法。
Pointcut（切入点）：被增强的方法是切入点。
Advice（通知/增强）：拦截到JoinPoint之后要做的事情。
- 前置通知
  - 事务前
- 后置通知
  - 事务后
- 异常通知
  - catch中
- 最终通知
  - finally中
- 环绕通知
  - 整个invoke
Target（目标对象\被代理对象）
Introduction（引介）：特殊的通知
Weaving（织入）：根据目标对象创建代理对象的过程
Proxy（代理）：织入增强后产生的代理类
Aspect（切面）：切入点和通知的结合

基于Spring的AOP编程

基于XML的AOP

配置XML文件

<bean id="logger" class="xyz.aiinirii.spring.utils.Logger"/>

<aop:config>
    <aop:aspect id="logAdvice" ref="logger">
        <!-- 类比在事务之前所做的事情 -->
        <aop:before method="beforePrintLog"
                    pointcut="execution(* xyz.aiinirii.spring.service.impl.*.*(..))"/>
        <!-- 类比在事务成功之后所做的事情 例如 commit -->
        <aop:after-returning method="afterReturningPrintLog"
                             pointcut="execution(* xyz.aiinirii.spring.service.impl.*.*(..))"/>
        <!-- 例如回滚 -->
        <aop:after-throwing method="afterThrowingPrintLog"
                            pointcut="execution(* xyz.aiinirii.spring.service.impl.*.*(..))"/>
        <!-- 例如关闭链接 -->
        <aop:after method="afterPrintLog"
                   pointcut="execution(* xyz.aiinirii.spring.service.impl.*.*(..))"/>
    </aop:aspect>
</aop:config>

运行效果，saveAccount方法得到了增强：

或者这样：

<bean id="logger" class="xyz.aiinirii.spring.utils.Logger"/>

<aop:config>
    <aop:pointcut id="serviceImpl" expression="execution(* xyz.aiinirii.spring.service.impl.*.*(..))"/>
    <aop:aspect id="logAdvice" ref="logger">
        <aop:before method="beforePrintLog"
                    pointcut-ref="serviceImpl"/>
        <aop:after-returning method="afterReturningPrintLog"
                             pointcut-ref="serviceImpl"/>
        <aop:after-throwing method="afterThrowingPrintLog"
                            pointcut-ref="serviceImpl"/>
        <aop:after method="afterPrintLog"
                   pointcut-ref="serviceImpl"/>
    </aop:aspect>
</aop:config>

环绕通知？

<bean id="logger" class="xyz.aiinirii.spring.utils.Logger"/>

<aop:config>
    <aop:pointcut id="serviceImpl" expression="execution(* xyz.aiinirii.spring.service.impl.*.*(..))"/>
    <aop:aspect id="logAdvice" ref="logger">
        <aop:around method="aroundPrintLog" pointcut-ref="serviceImpl"/>
    </aop:aspect>
</aop:config>

发现并没有执行被增强的函数。切入点方法没有执行，而通知方法执行了。

原因分析：并没有在环绕通知中调用切入点方法。

public Object aroundPrintLog(ProceedingJoinPoint joinPoint){
    Object rtValue = null;
    try {
        System.out.println("Before Print Log...");
        rtValue = joinPoint.proceed();
        System.out.println("After Return Print Log...");
    } catch (Throwable throwable) {
        System.out.println("After Throwing Print Log...");
        throwable.printStackTrace();
    } finally {
        System.out.println("After Print Log...");
    }
    return rtValue;
}

<bean id="logger" class="xyz.aiinirii.spring.utils.Logger"/>

<aop:config>
    <aop:pointcut id="serviceImpl" expression="execution(* xyz.aiinirii.spring.service.impl.*.*(..))"/>
    <aop:aspect id="logAdvice" ref="logger">
        <aop:around method="aroundPrintLog" pointcut-ref="serviceImpl"/>
    </aop:aspect>
</aop:config>

基于注解的AOP

<aop:aspectj-autoproxy/>

Logger 类，通知类：

import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.*;
import org.springframework.stereotype.Component;

/**
 * @author AIINIRII
 */
@Component("logger")
@Aspect
public class Logger {

    @Before("execution(* xyz.aiinirii.spring.service.impl.*.*(..))")
    public void beforePrintLog() {
        System.out.println("Before Print Log...");
    }

    @AfterReturning("execution(* xyz.aiinirii.spring.service.impl.*.*(..))")
    public void afterReturningPrintLog() {
        System.out.println("After Return Print Log...");
    }

    @AfterThrowing("execution(* xyz.aiinirii.spring.service.impl.*.*(..))")
    public void afterThrowingPrintLog() {
        System.out.println("After Throwing Print Log...");
    }

    @After("execution(* xyz.aiinirii.spring.service.impl.*.*(..))")
    public void afterPrintLog() {
        System.out.println("After Print Log...");
    }

    // @Around("execution(* xyz.aiinirii.spring.service.impl.*.*(..))")
    public Object aroundPrintLog(ProceedingJoinPoint joinPoint){
        Object rtValue = null;
        try {
            System.out.println("Before Print Log...");
            rtValue = joinPoint.proceed();
            System.out.println("After Return Print Log...");
        } catch (Throwable throwable) {
            System.out.println("After Throwing Print Log...");
            throwable.printStackTrace();
        } finally {
            System.out.println("After Print Log...");
        }
        return rtValue;
    }
}

AccountServiceImpl 类，Target 类：

import org.springframework.stereotype.Service;
import xyz.aiinirii.spring.service.IAccountService;

/**
 * @author AIINIRII
 */
@Service("accountService")
public class AccountServiceImpl implements IAccountService {

    public void saveAccount() {
        System.out.println("Successfully save the account.");
    }
}

总结

提取重复代码:arrow_right:创建代理对象

从而实现AOP

提示，尽量用@Around（）否则最终和异常/后置顺序将会出错。