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spring aop

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Architectural

Business Object

A business object is a normal class which has a normal business logic.

Aspect

An aspect is a modularization of a concern that cuts across multiple classes.

JoinPoint

A Joinpoint is a point during the execution of a program, such as execution of a method or the handling of an exception.

In Spring AOP, a JoinPoint always represents a method execution.

Pointcut

A Pointcut is a predicate that helps match an Advice to be applied by an Aspect at a particular JoinPoint.

The Advice is often associated with a Pointcut expression and runs at any Joinpoint matched by the Pointcut.

Advice

An advice is an action taken by an aspect at a particular Joinpoint. Different types of advice include “around,” “before” and “after” advice.

In Spring, an Advice is modeled as an interceptor, maintaining a chain of interceptors around the Joinpoint.

Example:Wiring Business Object and Aspect

  • Business Object

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    public class SampleAdder {
        public int add(int a, int b) {
            return a + b;
        }
    }

  • a simple Aspect

    Unified logging can be an example of such cross-cutting concern:

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    public class AdderAfterReturnAspect {
        private Logger logger = LoggerFactory.getLogger(this.getClass());
        public void afterReturn(Object returnValue) throws Throwable {
            logger.info("value return was {}",  returnValue);
        }
    }

  • config excerpt

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    <bean id="sampleAdder" class="org.xxx.SampleAdder" />
    <bean id="doAfterReturningAspect"
      class="org.xxx.AdderAfterReturnAspect" />
    <aop:config>
        <aop:aspect id="aspects" ref="doAfterReturningAspect">
           <aop:pointcut id="pointCutAfterReturning" expression=
             "execution(* org.xxx.SampleAdder+.*(..))"/>
           <aop:after-returning method="afterReturn"
             returning="returnValue" pointcut-ref="pointCutAfterReturning"/>
        </aop:aspect>
    </aop:config>

依赖注入DI有助于应用对象之间的解耦，而AOP可以实现横切关注点与它们所影响的对象之间的解耦

  • 通知Advice

    切面的工作被称为通知，通知定义了切面是什么以及何时使用。

    • 前置通知（Before）：在目标方法被调用之前调用通知功能
    • 后置通知（After）：在目标方法完成之后调用通知，此时不会关心方法的输出
    • 返回通知（After-returning）：在目标方法成功执行之后调用通知
    • 异常通知（After-throwing）：在目标方法抛出异常后调用通知
    • 环绕通知（Around）：通知包裹了被通知的方法，在被通知的方法调用之前和调用之后执行自定义的行为。

  • 连接点Join point

    连接点是应用程序的点，可供插入切面

    我理解的是程序的某处，或者任意一处都可以称作为连接点

  • 切点Pointcut

    切点有助于缩小切面所通知的连接点的范围

    如果Advice定义了切面的what和when,那么pointcut就定义了where

  • 切面Aspect

    Aspect是Advice和Pointcut的结合