Chapter 4: Spring AOP

4.1: Aspect-Oriented Programming 
    AOP is the programming idea of ​​cutting the code into the specified location of the class during runtime. Aspects can help us modularize cross-cutting concerns and realize the reuse of cross-cutting concerns. Spring implants the aspect into the specified bean during runtime, and actually inserts the aspect during the process of intercepting the method invocation. 
4.2: Describe pointcuts 
    The definition of pointcuts in SpringAOP uses AspectJ pointcut expressions. But only some of AspectJ's pointcut expressions are supported. arg(), @arg(), this(), target(), @target(), within() $within(), @annotation and execution(). Among these pointcut indicators, execution() is used to implement the matching, and other indicators are used to define the matching pointcut. 
    Pointcut case: 
        execution(* package.package.class.method(..)) 
        execution(* package.package.class.method(..) && within (package A.*)) //additional condition is: package A Any method under 
        execution(* package.package.class.method(..) && bean("beanID")) // additional condition is: match specific bean 
        execution(* package.package.class.method(. .) && !bean("beanID")) //additional condition is: does not match a specific bean 
        execution(* package.package.class.method(int) && args(property)) //pointcut 
4.3 with arguments: Create Aspects Using Annotations
    To use annotations to create aspects, you need to enable AspectJ's automatic proxy, and then use @After, @AfterReturning, @AfterThrowing, @Around, @Before annotations to create aspects with java classes. 
    Start AspectJ automatic proxy: start 
        in java configuration class: 
            @Configuration 
            @EnableAspectJAutoProxy //Start AspectJ automatic proxy 
            @ComponentScan 
            public class ConcertConfig(){@Bean...} 
        Start in xml: 
            <beans> 
                <aop:aspectJ-autoproxy > //Start AspectJ automatic proxy 
            </beans> 
    Use annotation to create aspect 
        package xxx; 
        /** 
        pointcut=aspect+advice 
        */ 
        @Aspect 
        public class Audience{ 
            //pointcut 
            @PointCut("execution(* package.package. class.method(..))")
            public void performance(){} //Used to carry the pointcut, the method body is not important, and then the method name can be used to call the aspect. 
            //Notification 
            @Before("performance()") 
            public void helloBefore(){System.out.println("Pre-notification execution")} 
            @AfterReturning("performance()") 
            public void helloAfterReturning(){System.out .println("Return to post-notification execution") 
            @AfterThrowing("performance()") 
            public void helloAfterThrowing(){System.out.println("Exception post-notification execution")} 
        } 
    Use annotations to create surround notification 
        package xxx; 
        @Aspect 
        public class Audience{ 
            // 
            Pointcut @PointCut("execution(* package.package.class.method(..))")
            public void performance(){}     //用于承载切点，方法体不重要，之后使用方法名可调用切面。
            //环绕通知
            @Around("performance()")
            public void helloAround(ProceedingJoinPoint jp){
                try{
                    //执行前置通知
                    jp.proceed();
                    //执行后置通知
                }catch(Throwable e){
                    //调用异常通知
                }
            }
        }
4.4：在xml中声明切面
    一般切面
        <aop:config>
            <aop:aspect ref = "audience">      //ref 引用了ID为audience的Bean,这个bean中定义了通知方法。
                <!--切点-->
                <aop:pointcut id = "performance" expression = "execution(* 包.包.类.方法(..))" />
                <!--环绕通知-->
                <aop:before pointcut-ref = "performance" method = "通知A" />
                <aop:after-returning pointcut-ref = "performance" method = "通知B" />
                <aop:after-throwing> pointcut-ref = "performance" method = "通知C'/>
            </aop:aspect>
        </aop:config>
    环绕通知切面
        <aop:config>
            <aop:aspect ref = "audience">
                <!--切点-->
                <aop:pointcut id = "performance" expression = "execution(* 包.包.类.方法(..))" />
                <!--环绕通知-->
                <aop:around pointcut-ref = "performance" method = "helloAround">        //指点环绕通知方法
            </aop:aspect>
        </aop:config>
4.5：注入AspectJ切面
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