13.3、异常处理——DefaultHandlerExceptionResolver

当程序发生异常时，DefaultHandlerExceptionResolver异常解析器默认可以解析指定的异常，见下面的源码，默认可以解析HttpRequestMethodNotSupportedException、HttpMediaTypeNotSupportedException等异常类，当有这些类的异常发生时，默认交给DefaultHandlerExceptionResolver异常解析器进行解析，DispatcherServlet默认实现了DispatcherServlet 的Bean。

DefaultHandlerExceptionResolver源码

    @Override    @Nullable    protected ModelAndView doResolveException(HttpServletRequest request, HttpServletResponse response,            @Nullable Object handler, Exception ex) {        try {            if (ex instanceof HttpRequestMethodNotSupportedException) {                return handleHttpRequestMethodNotSupported((HttpRequestMethodNotSupportedException) ex, request,                        response, handler);            }            else if (ex instanceof HttpMediaTypeNotSupportedException) {                return handleHttpMediaTypeNotSupported((HttpMediaTypeNotSupportedException) ex, request, response,                        handler);            }            else if (ex instanceof HttpMediaTypeNotAcceptableException) {                return handleHttpMediaTypeNotAcceptable((HttpMediaTypeNotAcceptableException) ex, request, response,                        handler);            }            else if (ex instanceof MissingPathVariableException) {                return handleMissingPathVariable((MissingPathVariableException) ex, request,                        response, handler);            }            else if (ex instanceof MissingServletRequestParameterException) {                return handleMissingServletRequestParameter((MissingServletRequestParameterException) ex, request,                        response, handler);            }            else if (ex instanceof ServletRequestBindingException) {                return handleServletRequestBindingException((ServletRequestBindingException) ex, request, response,                        handler);            }            else if (ex instanceof ConversionNotSupportedException) {                return handleConversionNotSupported((ConversionNotSupportedException) ex, request, response, handler);            }            else if (ex instanceof TypeMismatchException) {                return handleTypeMismatch((TypeMismatchException) ex, request, response, handler);            }            else if (ex instanceof HttpMessageNotReadableException) {                return handleHttpMessageNotReadable((HttpMessageNotReadableException) ex, request, response, handler);            }            else if (ex instanceof HttpMessageNotWritableException) {                return handleHttpMessageNotWritable((HttpMessageNotWritableException) ex, request, response, handler);            }            else if (ex instanceof MethodArgumentNotValidException) {                return handleMethodArgumentNotValidException((MethodArgumentNotValidException) ex, request, response,                        handler);            }            else if (ex instanceof MissingServletRequestPartException) {                return handleMissingServletRequestPartException((MissingServletRequestPartException) ex, request,                        response, handler);            }            else if (ex instanceof BindException) {                return handleBindException((BindException) ex, request, response, handler);            }            else if (ex instanceof NoHandlerFoundException) {                return handleNoHandlerFoundException((NoHandlerFoundException) ex, request, response, handler);            }            else if (ex instanceof AsyncRequestTimeoutException) {                return handleAsyncRequestTimeoutException(                        (AsyncRequestTimeoutException) ex, request, response, handler);            }        }        catch (Exception handlerException) {            if (logger.isWarnEnabled()) {                logger.warn("Handling of [" + ex.getClass().getName() + "] resulted in Exception", handlerException);            }        }        return null;    }

下面以HttpRequestMethodNotSupportedException为例来测试，当发生HttpRequestMethodNotSupportedException异常时，会有DefaultHandlerExceptionResolver异常解析器进行处理。
1、web.xml和spring的配置文件
web.xml

<?xml version="1.0" encoding="UTF-8"?><web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"    xmlns="http://xmlns.jcp.org/xml/ns/javaee"    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"    id="WebApp_ID" version="3.1">    <!-- The front controller of this Spring Web application, responsible for handling all application requests -->    <servlet>        <servlet-name>springDispatcherServlet</servlet-name>        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>        <init-param>            <param-name>contextConfigLocation</param-name>            <param-value>classpath:springmvc.xml</param-value>        </init-param>        <load-on-startup>1</load-on-startup>    </servlet>    <!-- Map all requests to the DispatcherServlet for handling -->    <servlet-mapping>        <servlet-name>springDispatcherServlet</servlet-name>        <url-pattern>/</url-pattern>    </servlet-mapping></web-app>

spring的配置文件springmvc.xml

<?xml version="1.0" encoding="UTF-8"?><beans xmlns="http://www.springframework.org/schema/beans"    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"    xmlns:aop="http://www.springframework.org/schema/aop"    xmlns:context="http://www.springframework.org/schema/context"    xmlns:mvc="http://www.springframework.org/schema/mvc"    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd        http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-4.0.xsd        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.0.xsd        http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-4.0.xsd">    <context:component-scan base-package="com.lzj.springmvc"></context:component-scan>    <!--配置视图解析器-->    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">        <property name="prefix" value="/WEB-INF/views/"></property>        <property name="suffix" value=".jsp"></property>    </bean>    <mvc:annotation-driven></mvc:annotation-driven></beans>

2、创建请求
在WebContent下面创建index.jsp，内容为：

<a href="springMVC/testDefaultHandlerExceptionResolver">Test DefaultHandlerExceptionResolver</a>

3、创建请求控制器
控制器用于截获index.jsp中的请求

@Controller@RequestMapping("/springMVC")public class TestSpringMVC {    //设置默认接收POST请求    @RequestMapping(value="/testDefaultHandlerExceptionResolver", method=RequestMethod.POST)    public String testDefaultHandlerExceptionResolver(){        System.out.println("testDefaultHandlerExceptionResolver");        return "success";    }}

当发送Index.jsp请求时，由于index.jsp中的超链接请求为GET请求，当控制器截获该请求后，由于控制器设置的默认接收POST请求，因此会抛出一个HttpRequestMethodNotSupportedException异常，该异常默认由DefaultHandlerExceptionResolver解析器进行解析，返回个客户端异常界面，如下图所示：

浏览器中显示不支持GET请求。