【框架学习】AOP切面详解

spring、springMVC、SpringBoot这一系列对AOP都有很好的支持（其实都是Spring管理的）

一。概念

（1）面向切面编程，实际上就是给某个方法（或者某些），做一个代理，，很抽象？代理模式详解

代理可以抽象出来，为类似方法进行代理，，从而降低代码量，（相同的功能，如关闭流什么的，只写一次，不仅方便维护，大大减少了工作量）

（2）切点，

指的是，对那个方法进行代理，或者某些方法。

切点方法需要 @Pointcut

@Pointcut("execution(public * xatu.zsl.contoller.*.*(..))")
public void poincut(){}

（3）通知

即对 被代理方法，加上的操作。

前置通知 @Before(“poincut()”)

后置通知 @After(“poincut()”)

返回时通知 @AfterReturning(pointcut = “poincut()”,returning = “object”) returning指定返回对象。

抛出异常时通知 @AfterThrowing(“poincut()”)

环绕通知 @Around(“poincut()”)

二。使用

前置通知 @Before(“poincut()”)

@Before("poincut()")
public void before(JoinPoint joinPoint){
logger.info("before");
ServletRequestAttributes attributes = (ServletRequestAttributes) RequestContextHolder.getRequestAttributes();
HttpServletRequest request = attributes.getRequest();
//获取URL
logger.info("url={}",request.getRequestURL());
//请求方法
logger.info("mathod={}",request.getMethod());
//ip
logger.info("ip={}",request.getRemoteAddr());
//类方法
logger.info("class_method{}",joinPoint.getSignature().getDeclaringTypeName()+"."+joinPoint.getSignature().getName());
//参数
logger.info("args={}",joinPoint.getArgs());
}

后置通知 @After(“poincut()”)

@After("poincut()")
public void after(){
logger.info("after");
}

返回时通知 @AfterReturning(pointcut = “poincut()”,returning = “object”) returning指定返回对象。

@AfterReturning(pointcut = "poincut()",returning = "object")
public void afterReturning(Object object){
logger.info("return = {}",object.toString());
//        logger.info("return = ");
}

抛出异常时通知 @AfterThrowing(“poincut()”)

@AfterThrowing("poincut()")
public void afterThrowing(){
logger.info("抛出异常了。");
}

环绕通知 @Around(“poincut()”)

@Around("poincut()")
public void around(ProceedingJoinPoint joinPoint) throws Throwable {
logger.info("环绕通知。");
joinPoint.proceed();
}

三。细节

（1）

@AfterReturning和 @Around(“poincut()”)，，，会有特殊冲突，，搞了半天

SpringBoot中会出现空指针异常

Spring中启动时会出现错误无法启动，错误代码如下：解决方法（注释掉，@Around(“poincut()”)）

警告: Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'userService' defined in file [G:\work_space\study_spring\spring_demo\target\classes\xatu\zsl\service\UserServiceImpl.class]: Initialization of bean failed; nested exception is java.lang.IllegalArgumentException: error at ::0 can't find referenced pointcut poincut
Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'userService' defined in file [G:\work_space\study_spring\spring_demo\target\classes\xatu\zsl\service\UserServiceImpl.class]: Initialization of bean failed; nested exception is java.lang.IllegalArgumentException: error at ::0 can't find referenced pointcut poincut
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:553)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:482)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:776)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:861)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:541)
at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:139)
at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:83)
at xatu.zsl.MainTest.main(MainTest.java:16)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)
Caused by: java.lang.IllegalArgumentException: error at ::0 can't find referenced pointcut poincut
at org.aspectj.weaver.tools.PointcutParser.parsePointcutExpression(PointcutParser.java:301)
at org.springframework.aop.aspectj.AspectJExpressionPointcut.buildPointcutExpression(AspectJExpressionPointcut.java:207)
at org.springframework.aop.aspectj.AspectJExpressionPointcut.checkReadyToMatch(AspectJExpressionPointcut.java:193)
at org.springframework.aop.aspectj.AspectJExpressionPointcut.getClassFilter(AspectJExpressionPointcut.java:170)
at org.springframework.aop.support.AopUtils.canApply(AopUtils.java:220)
at org.springframework.aop.support.AopUtils.canApply(AopUtils.java:279)
at org.springframework.aop.support.AopUtils.findAdvisorsThatCanApply(AopUtils.java:311)
at org.springframework.aop.framework.autoproxy.AbstractAdvisorAutoProxyCreator.findAdvisorsThatCanApply(AbstractAdvisorAutoProxyCreator.java:118)
at org.springframework.aop.framework.autoproxy.AbstractAdvisorAutoProxyCreator.findEligibleAdvisors(AbstractAdvisorAutoProxyCreator.java:88)
at org.springframework.aop.framework.autoproxy.AbstractAdvisorAutoProxyCreator.getAdvicesAndAdvisorsForBean(AbstractAdvisorAutoProxyCreator.java:69)
at org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator.wrapIfNecessary(AbstractAutoProxyCreator.java:347)
at org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator.postProcessAfterInitialization(AbstractAutoProxyCreator.java:299)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsAfterInitialization(AbstractAutowireCapableBeanFactory.java:422)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1583)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:545)
... 16 more

（2）JoinPoint joinPoint，参数不能出现在afterReturning()，，中，，不知道为什么，，容易出错，，