界说一个切面来处理日志纪录和执行时间盘算：
@Aspect@ComponentpublicclassPerformanceLoggingAspect{privatestaticfinalLoggerlogger=LoggerFactory.getLogger(PerformanceLoggingAspect.class);@Before("execution(*com.example.service.UserService.*(..))")publicvoidlogBeforeMethod(){logger.info("Methodexecutionstarted...");}@AfterReturning(pointcut="execution(*com.example.service.UserService.*(..))",returning="result")publicvoidlogAfterMethod(Objectresult){longexecutionTime=System.currentTimeMillis()-startTime;logger.info("Methodexecutioncompleted.Result:"+result+".Executiontime:"+executionTime+"ms");}}
}
####8.2事务治理事务治理是另一个重要的应用场景。通过界说一个切面，可以在需要事务控制的要领上添加事务通知。
java@Aspect@ComponentpublicclassTransactionAspect{
@Around("execution(*com.example.service.*.*(..))")publicObjectmanageTransaction(ProceedingJoinPointjoinPoint)throwsThrowable{TransactionStatusstatus=TransactionAspectSupport.createTransactionStatus();try{TransactionAspectSupport.startTransaction();Objectresult=joinPoint.proceed();TransactionAspectSupport.commitTransaction(status);returnresult;}catch(Exceptione){TransactionAspectSupport.rollbackTransaction(status);throwe;}}
1围绕通知
围绕通知是AOP中最强大的通知类型，它可以在目标要领执行前后进行自界说操作，甚至可以完全替代?目标要领的执行。例如：
@AspectpublicclassPerformanceLoggingAspect{privatestaticfinalLoggerlogger=LoggerFactory.getLogger(PerformanceLoggingAspect.class);@Around("execution(*com.example.service.UserService.*(..))")publicObjectlogAroundMethod(ProceedingJoinPointjoinPoint)throwsThrowable{logger.info("Methodexecutionstarted...");longstartTime=System.currentTimeMillis();Objectresult=joinPoint.proceed();//CalltheactualmethodlongexecutionTime=System.currentTimeMillis()-startTime;logger.info("Methodexecutioncompleted.Result:"+result+".Executiontime:"+executionTime+"ms");returnresult;}}在这个例子中，我们使用了`@Around`注解界说了一个围绕通知，它在目标要领执行前后进行了日志纪录和执行时间盘算。
privatestaticfinalLoggerlogger=LoggerFactory.getLogger(LoggingAspect.class);@Before("execution(*com.example.service.*.*(..))")publicvoidlogBeforeMethod(){logger.info("Methodexecutionstarted...");}@AfterReturning(pointcut="execution(*com.example.service.*.*(..))",returning="result")publicvoidlogAfterMethod(Objectresult){logger.info("Methodexecutioncompleted.Result:"+result);}
2强大的通知机制
通知（Advice）是AOP的焦点看法。好色先生支持多种类型的?通知，如前置通知（Before）、后置通知（After）、返回通知（AfterReturning）、异常通知（AfterThrowing）等?。例如：
@After("execution(*com.example.service.*.*(..))")publicvoidafterMethod(){System.out.println("Methodexecutioncompleted.");}
校对：朱广权(1C0m4pJyqZtPma0S7t9ZFfz4hTykKag)