(36)通知与切面-编程实验室

通知类型

通知类型包括：

前置通知：@Before 目标方法执行之前的通知
后置通知：@AfterReturning 目标方法执行之后的通知
环绕通知：@Around 目标方法之前添加通知，同时目标方法执行之后添加通知。
异常通知：@AfterThrowing 发生异常之后执行的通知
最终通知：@After 放在finally语句块中的通知

接下来，编写程序来测试这几个通知的执行顺序：

packagecom.powernode.spring6.service;importorg.aspectj.lang.ProceedingJoinPoint;importorg.aspectj.lang.annotation.*;importorg.springframework.stereotype.Component;// 切面类@Component@AspectpublicclassMyAspect{@Around("execution(* com.powernode.spring6.service.OrderService.*(..))")publicvoidaroundAdvice(ProceedingJoinPointproceedingJoinPoint)throwsThrowable{System.out.println("环绕通知开始");// 执行目标方法。proceedingJoinPoint.proceed();System.out.println("环绕通知结束");}@Before("execution(* com.powernode.spring6.service.OrderService.*(..))")publicvoidbeforeAdvice(){System.out.println("前置通知");}@AfterReturning("execution(* com.powernode.spring6.service.OrderService.*(..))")publicvoidafterReturningAdvice(){System.out.println("后置通知");}@AfterThrowing("execution(* com.powernode.spring6.service.OrderService.*(..))")publicvoidafterThrowingAdvice(){System.out.println("异常通知");}@After("execution(* com.powernode.spring6.service.OrderService.*(..))")publicvoidafterAdvice(){System.out.println("最终通知");}}

packagecom.powernode.spring6.service;importorg.springframework.stereotype.Component;// 目标类@ComponentpublicclassOrderService{// 目标方法publicvoidgenerate(){System.out.println("订单已生成！");}}

packagecom.powernode.spring6.test;importcom.powernode.spring6.service.OrderService;importorg.junit.Test;importorg.springframework.context.ApplicationContext;importorg.springframework.context.support.ClassPathXmlApplicationContext;publicclassAOPTest{@TestpublicvoidtestAOP(){ApplicationContextapplicationContext=newClassPathXmlApplicationContext("spring-aspectj-aop-annotation.xml");OrderServiceorderService=applicationContext.getBean("orderService",OrderService.class);orderService.generate();}}

执行结果：

通过上面的执行结果就可以判断他们的执行顺序了，这里不再赘述。
结果中没有异常通知，这是因为目标程序执行过程中没有发生异常。我们尝试让目标方法发生异常：

packagecom.powernode.spring6.service;importorg.springframework.stereotype.Component;// 目标类@ComponentpublicclassOrderService{// 目标方法publicvoidgenerate(){System.out.println("订单已生成！");if(1==1){thrownewRuntimeException("模拟异常发生");}}}

再次执行测试程序，结果如下：

通过测试得知，当发生异常之后，最终通知也会执行，因为最终通知@After会出现在finally语句块中。
出现异常之后，后置通知和环绕通知的结束部分不会执行。

切面的先后顺序

我们知道，业务流程当中不一定只有一个切面，可能有的切面控制事务，有的记录日志，有的进行安全控制，如果多个切面的话，顺序如何控制：可以使用@Order注解来标识切面类，为@Order注解的value指定一个整数型的数字，数字越小，优先级越高。
再定义一个切面类，如下：

packagecom.powernode.spring6.service;importorg.aspectj.lang.ProceedingJoinPoint;importorg.aspectj.lang.annotation.*;importorg.springframework.core.annotation.Order;importorg.springframework.stereotype.Component;@Aspect@Component@Order(1)//设置优先级publicclassYourAspect{@Around("execution(* com.powernode.spring6.service.OrderService.*(..))")publicvoidaroundAdvice(ProceedingJoinPointproceedingJoinPoint)throwsThrowable{System.out.println("YourAspect环绕通知开始");// 执行目标方法。proceedingJoinPoint.proceed();System.out.println("YourAspect环绕通知结束");}@Before("execution(* com.powernode.spring6.service.OrderService.*(..))")publicvoidbeforeAdvice(){System.out.println("YourAspect前置通知");}@AfterReturning("execution(* com.powernode.spring6.service.OrderService.*(..))")publicvoidafterReturningAdvice(){System.out.println("YourAspect后置通知");}@AfterThrowing("execution(* com.powernode.spring6.service.OrderService.*(..))")publicvoidafterThrowingAdvice(){System.out.println("YourAspect异常通知");}@After("execution(* com.powernode.spring6.service.OrderService.*(..))")publicvoidafterAdvice(){System.out.println("YourAspect最终通知");}}

packagecom.powernode.spring6.service;importorg.aspectj.lang.ProceedingJoinPoint;importorg.aspectj.lang.annotation.*;importorg.springframework.core.annotation.Order;importorg.springframework.stereotype.Component;// 切面类@Component@Aspect@Order(2)//设置优先级publicclassMyAspect{@Around("execution(* com.powernode.spring6.service.OrderService.*(..))")publicvoidaroundAdvice(ProceedingJoinPointproceedingJoinPoint)throwsThrowable{System.out.println("环绕通知开始");// 执行目标方法。proceedingJoinPoint.proceed();System.out.println("环绕通知结束");}@Before("execution(* com.powernode.spring6.service.OrderService.*(..))")publicvoidbeforeAdvice(){System.out.println("前置通知");}@AfterReturning("execution(* com.powernode.spring6.service.OrderService.*(..))")publicvoidafterReturningAdvice(){System.out.println("后置通知");}@AfterThrowing("execution(* com.powernode.spring6.service.OrderService.*(..))")publicvoidafterThrowingAdvice(){System.out.println("异常通知");}@After("execution(* com.powernode.spring6.service.OrderService.*(..))")publicvoidafterAdvice(){System.out.println("最终通知");}}

执行测试程序：

通过修改@Order注解的整数值来切换顺序，执行测试程序：

优化使用切点表达式

观看以下代码中的切点表达式：

packagecom.powernode.spring6.service;importorg.aspectj.lang.ProceedingJoinPoint;importorg.aspectj.lang.annotation.*;importorg.springframework.core.annotation.Order;importorg.springframework.stereotype.Component;// 切面类@Component@Aspect@Order(2)publicclassMyAspect{@Around("execution(* com.powernode.spring6.service.OrderService.*(..))")publicvoidaroundAdvice(ProceedingJoinPointproceedingJoinPoint)throwsThrowable{System.out.println("环绕通知开始");// 执行目标方法。proceedingJoinPoint.proceed();System.out.println("环绕通知结束");}@Before("execution(* com.powernode.spring6.service.OrderService.*(..))")publicvoidbeforeAdvice(){System.out.println("前置通知");}@AfterReturning("execution(* com.powernode.spring6.service.OrderService.*(..))")publicvoidafterReturningAdvice(){System.out.println("后置通知");}@AfterThrowing("execution(* com.powernode.spring6.service.OrderService.*(..))")publicvoidafterThrowingAdvice(){System.out.println("异常通知");}@After("execution(* com.powernode.spring6.service.OrderService.*(..))")publicvoidafterAdvice(){System.out.println("最终通知");}}

缺点是：

第一：切点表达式重复写了多次，没有得到复用。
第二：如果要修改切点表达式，需要修改多处，难维护。

可以这样做：将切点表达式单独的定义出来，在需要的位置引入即可。如下：

packagecom.powernode.spring6.service;importorg.aspectj.lang.ProceedingJoinPoint;importorg.aspectj.lang.annotation.*;importorg.springframework.core.annotation.Order;importorg.springframework.stereotype.Component;// 切面类@Component@Aspect@Order(2)publicclassMyAspect{@Pointcut("execution(* com.powernode.spring6.service.OrderService.*(..))")publicvoidpointcut(){}@Around("pointcut()")publicvoidaroundAdvice(ProceedingJoinPointproceedingJoinPoint)throwsThrowable{System.out.println("环绕通知开始");// 执行目标方法。proceedingJoinPoint.proceed();System.out.println("环绕通知结束");}@Before("pointcut()")publicvoidbeforeAdvice(){System.out.println("前置通知");}@AfterReturning("pointcut()")publicvoidafterReturningAdvice(){System.out.println("后置通知");}@AfterThrowing("pointcut()")publicvoidafterThrowingAdvice(){System.out.println("异常通知");}@After("pointcut()")publicvoidafterAdvice(){System.out.println("最终通知");}}