springmvc异常处理

Spring MVC 通过 HandlerExceptionResolver  处理程序的异常，包括 Handler 映射、数据绑定以及目标方法执行时发生的异常。

SpringMVC 提供的 HandlerExceptionResolver 的实现类

DispatcherServlet  默认装配的 HandlerExceptionResolver ：

①     使用了 <mvc:annotation-driven/> 配置：

1.    ExceptionHandlerExceptionResolver

1)主要处理 Handler 中用 @ExceptionHandler 注解定义的方法

2)@ExceptionHandler 注解定义的方法优先级问题：例如发生的是NullPointerException，但是声明的异常有 RuntimeException 和 Exception，此候会根据异常的最近继承关系找到继承深度最浅的那个 @ExceptionHandler 注解方法，即标记了 RuntimeException 的方法

3)ExceptionHandlerMethodResolver 内部若找不到@ExceptionHandler 注解的话，会找 @ControllerAdvice 中的@ExceptionHandler 注解方法

2.    异常处理_ResponseStatusExceptionResolver

3.    异常处理_DefaultHandlerExceptionResolver

对一些特殊的异常进行处理，比如：

NoSuchRequestHandlingMethodException、

HttpRequestMethodNotSupportedException、

HttpMediaTypeNotSupportedException、

HttpMediaTypeNotAcceptableException等。

4.    异常处理_SimpleMappingExceptionResolver

如果希望对所有异常进行统一处理，可以使用 SimpleMappingExceptionResolver，它将异常类名映射为视图名，即发生异常时使用对应的视图报告异常

<!--简单异常映射解析器，对于用户 名存在throw的异常进行映射跳转到指定视图  -->
    <bean id="SimpleMappingExceptionResolver" class="org.springframework.web.servlet.handler.SimpleMappingExceptionResolver">
        <property name="exceptionMappings">
            <!-- key属性是异常类型 -->
            <!-- 标签体配置目标视图 -->
            <props>
                <prop key="com.lamsey.survey.e.UserNameAlreadyExistException">guest/user_regist</prop>
            </props>        
        </property>
    </bean>

 源码分析：

首先springmvc核心流程如下：

四步：

1）、所有请求进来都经过DispatcherServlet的900：doDispatch()方法（包含了处理请求以及响应的所有流程）

2）、916；getHandler(processedRequest);根据当前请求获取到能处理这个请求的Controller对象

3）、923：找到能执行这个Controller对象里面每一个方法的适配器

4）、945：ha.handle适配器调用目标方法（利用反射调用方法）

5）、959：转发到页面（处理响应结果）processDispatchResult

异常处理在processDispatchResult（）

private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
            HandlerExecutionChain mappedHandler, ModelAndView mv, Exception exception) throws Exception {

        boolean errorView = false;

        if (exception != null) {
            if (exception instanceof ModelAndViewDefiningException) {
                logger.debug("ModelAndViewDefiningException encountered", exception);
                mv = ((ModelAndViewDefiningException) exception).getModelAndView();
            }
            else {
                Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
               //处理异常
                mv = processHandlerException(request, response, handler, exception);
                errorView = (mv != null);
            }
        }

        // Did the handler return a view to render?
        if (mv != null && !mv.wasCleared()) {
          //这是正常的页面渲染流程
            render(mv, request, response);
            if (errorView) {
                WebUtils.clearErrorRequestAttributes(request);
            }
        }
        else {
            if (logger.isDebugEnabled()) {
                logger.debug("Null ModelAndView returned to DispatcherServlet with name '" + getServletName() +
                        "': assuming HandlerAdapter completed request handling");
            }
        }

        if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
            // Concurrent handling started during a forward
            return;
        }

        if (mappedHandler != null) {
            mappedHandler.triggerAfterCompletion(request, response, null);
        }
    }

1）判断有无异常

//处理异常
                mv = processHandlerException(request, response, handler, exception);

2）对视图进行渲染

 //这是正常的页面渲染流程
            render(mv, request, response);

遍历获取异常处理解析器

protected ModelAndView processHandlerException(HttpServletRequest request, HttpServletResponse response,
            Object handler, Exception ex) throws Exception {

        // Check registered HandlerExceptionResolvers...
        ModelAndView exMv = null;

        for (HandlerExceptionResolver handlerExceptionResolver : this.handlerExceptionResolvers) {
            exMv = handlerExceptionResolver.resolveException(request, response, handler, ex);
            if (exMv != null) {
                break;
            }
        }
        if (exMv != null) {
            if (exMv.isEmpty()) {
                return null;
            }
            // We might still need view name translation for a plain error model...
            if (!exMv.hasView()) {
                exMv.setViewName(getDefaultViewName(request));
            }
            if (logger.isDebugEnabled()) {
                logger.debug("Handler execution resulted in exception - forwarding to resolved error view: " + exMv, ex);
            }
            WebUtils.exposeErrorRequestAttributes(request, ex, getServletName());
            return exMv;
        }

        throw ex;
    }

SpringMVC默认定制页面的异常如下；

try {
            if (ex instanceof NoSuchRequestHandlingMethodException) {
                return handleNoSuchRequestHandlingMethod((NoSuchRequestHandlingMethodException) ex, request, response,
                        handler);
            }
            else 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 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);
            }
        }
        catch (Exception handlerException) {
            logger.warn("Handling of [" + ex.getClass().getName() + "] resulted in Exception", handlerException);
        }
        return null;
    }