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文章目录

二、全局异常拦截点2-1、入口2-2、全局异常拦截器是如何注入到

DispatcherServlet

四、其它4-1、设置HTTP状态码4-2、异常处理器排序4-3、所谓全局异常

最近在做系统升级的时候引发了一个BUG原本系统是有一个异常处理器A引入了某个底包中也带了一个异常处理器B最终走了底包的异常处理器B。

A对于异常的时候会返回HTTP状态码为500B对于异常处理器返回的HTTP状态码为200前端基于HTTP状态码进行提示的就出了问题

本篇文章我们就来讨论一下在JavaWeb中的全局异常处理器是何时何地如何执行的。

在进行学习之前需要先知道HTTP执行流程SpringMVC执行流程

HandlerExceptionResolver简单来说就是实现或间接实现它的类就叫全局异常处理器。

package

org.springframework.web.servlet;import

javax.servlet.http.HttpServletRequest;

import

javax.servlet.http.HttpServletResponse;

import

org.springframework.lang.Nullable;public

interface

resolveException(HttpServletRequest

request,

SpringBoot项目最大的特点就是注解在SpringBoot项目中全局异常拦截的注解是ControllerAdvice

RestControllerAdvice

ExceptionHandlerExceptionResolver

1-2、实现方式二

doResolveHandlerMethodException

public

AbstractHandlerMethodExceptionResolver

{private

LoggerFactory.getLogger(ExceptionHandler.class);Overrideprotected

ModelAndView

doResolveHandlerMethodException(HttpServletRequest

request,

org.springframework.web.servlet.DispatcherServlet#doDispatch

这个方法就是SpringMVC的执行流程的核心代码了下面是简化代码

protected

WebAsyncUtils.getAsyncManager(request);try

{ModelAndView

异常处理的入口processDispatchResult(processedRequest,

response,

}org.springframework.web.servlet.DispatcherServlet#processDispatchResult

private

processDispatchResult(HttpServletRequest

request,

processHandlerException(request,

response,

}org.springframework.web.servlet.DispatcherServlet#processHandlerException

protected

processHandlerException(HttpServletRequest

request,

typesrequest.removeAttribute(HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE);//

Check

HandlerExceptionResolvers...ModelAndView

exMv

(this.handlerExceptionResolvers

null)

this.handlerExceptionResolvers)

{exMv

resolver.resolveException(request,

response,

handlerExceptionResolvers;在DispatcherServlet里面有一个onRefresh方法它是重写的父类FrameworkServlet的在初始化ServletBean的时候会被调用一次它里面会做很多初始化的操作其中一个就是获取容器里面的全局异常拦截器

Override

initStrategies(ApplicationContext

context)

...initHandlerExceptionResolvers(context);//

...

initHandlerExceptionResolvers(ApplicationContext

context)

{this.handlerExceptionResolvers

null;if

(this.detectAllHandlerExceptionResolvers)

{//

HandlerExceptionResolverMapString,

matchingBeans

BeanFactoryUtils.beansOfTypeIncludingAncestors(context,

HandlerExceptionResolver.class,

true,

{this.handlerExceptionResolvers

new

ArrayList(matchingBeans.values());//

排序AnnotationAwareOrderComparator.sort(this.handlerExceptionResolvers);}}//

...

ExceptionHandlerExceptionResolver

package

org.springframework.web.servlet.mvc.method.annotation;public

class

ExceptionHandlerExceptionResolver

extends

AbstractHandlerMethodExceptionResolverimplements

InitializingBean

}⚠️可以回到【全局异常处理器的类型】的图看看ExceptionHandlerExceptionResolver其实就是全局异常处理器HandlerExceptionResolver的子类

InitializingBean重写了afterPropertiesSet这个方法会在bean初始化完之后执行

Override

beansinitExceptionHandlerAdviceCache();//

...

}initExceptionHandlerAdviceCache

private

initExceptionHandlerAdviceCache()

{if

ControllerAdviceBean.findAnnotatedBeans(getApplicationContext());for

adviceBean

IllegalStateException(Unresolvable

type

注解ExceptionHandlerMethodResolver

resolver

ExceptionHandlerMethodResolver(beanType);if

(resolver.hasExceptionMappings())

{//

存入当前的类参数里面this.exceptionHandlerAdviceCache.put(adviceBean,

resolver);}if

(ResponseBodyAdvice.class.isAssignableFrom(beanType))

{this.responseBodyAdvice.add(adviceBean);}}//

...

}org.springframework.web.method.ControllerAdviceBean#findAnnotatedBeans

public

findAnnotatedBeans(ApplicationContext

context)

ConfigurableApplicationContext)

{//

((ConfigurableApplicationContext)

context).getBeanFactory();}ListControllerAdviceBean

adviceBeans

BeanFactoryUtils.beanNamesForTypeIncludingAncestors(beanFactory,

Object.class))

(!ScopedProxyUtils.isScopedTarget(name))

{//

beanFactory.findAnnotationOnBean(name,

(controllerAdvice

排序OrderComparator.sort(adviceBeans);return

adviceBeans;

中org.springframework.web.method.annotation.ExceptionHandlerMethodResolver#ExceptionHandlerMethodResolver

public

ExceptionHandlerMethodResolver(Class?

handlerType)

MethodIntrospector.selectMethods(handlerType,

{for

detectExceptionMappings(method))

{addExceptionMapping(exceptionType,

method);}}

this.mappedMethods.put(exceptionType,

method);if

IllegalStateException(Ambiguous

ExceptionHandler

生成了一个ExceptionHandlerExceptionResolver它通过多级实现了

HandlerExceptionResolver所有使用ControllerAdvice的类都存在了

中所有使用

HandlerExceptionResolver.resolveException方法它只有这一个方法从【3-1】得知所有使用

ControllerAdvice

注解的类都被存在了ExceptionHandlerExceptionResolver

中从【1】得知ExceptionHandlerExceptionResolver的继承关系如下图

这个很简单直接去看即可org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver#doResolveHandlerMethodException

执行过程就是循环exceptionHandlerAdviceCache中的每一个全局拦截器再循环每个拦截器里面的mappedMethods看哪个可以匹配上就执行哪个

四、其它

大多数情况下我们会自定义返回值code比如未鉴权返回给前端HTTP状态码是200code为401但在某些情况下也会直接返回HTTP状态码401可以使用

ResponseStatus

ResponseStatus(HttpStatus.UNAUTHORIZED)

ExceptionHandler(Exception.class)

public

并不是系统任何异常都会被它所拦截因为我们已经知道它的执行点是在MVC的流程中所以就只有HTTP异常才会被拦截处理