springmvc 报无法解析视图异常

        最近，前端nginx的日志一直在报一些URL的请求后端响应是500状态码，于是缓存其结果，可以看到一直是报一个 javax.servlet.ServletException: Could not resolve view with name 'xxxx'in servlet with name 'Spring MVC Dispatcher Servlet ‘的异常。

        分析这些报这个异常的的URL，规则都是/xxx/{xxx}，报错的URL都是类似于 /xxx/xxx.jpg之类的跟着后缀的，我们的资源内容中也就是这个路由是对应的是没有这个jpg的资源的，也就是说自然会是404，但是404竟然也报这个异常和500错误码。

        看了springmvc关于这个异常的出处,很明显的是View为null，而view是由resolveViewName获得的。

protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {
		// Determine locale for request and apply it to the response.
		Locale locale = this.localeResolver.resolveLocale(request);
		response.setLocale(locale);

		View view;
		if (mv.isReference()) {
			// We need to resolve the view name.
			view = resolveViewName(mv.getViewName(), mv.getModelInternal(), locale, request);
			if (view == null) {
				throw new ServletException(
						"Could not resolve view with name '" + mv.getViewName() + "' in servlet with name '" +
								getServletName() + "'");
			}
		}
......
}

        我们接下来继续看resolveViewName实现。
        

	protected View resolveViewName(String viewName, Map<String, Object> model, Locale locale,
			HttpServletRequest request) throws Exception {

		for (ViewResolver viewResolver : this.viewResolvers) {
			View view = viewResolver.resolveViewName(viewName, locale);
			if (view != null) {
				return view;
			}
		}
		return null;
	}

public View resolveViewName(String viewName, Locale locale) throws Exception {
		RequestAttributes attrs = RequestContextHolder.getRequestAttributes();
		Assert.isInstanceOf(ServletRequestAttributes.class, attrs);
		List<MediaType> requestedMediaTypes = getMediaTypes(((ServletRequestAttributes) attrs).getRequest());
		if (requestedMediaTypes != null) {
			List<View> candidateViews = getCandidateViews(viewName, locale, requestedMediaTypes);
			View bestView = getBestView(candidateViews, requestedMediaTypes);
			if (bestView != null) {
				return bestView;
			}
		}
		if (this.useNotAcceptableStatusCode) {
			if (logger.isDebugEnabled()) {
				logger.debug("No acceptable view found; returning 406 (Not Acceptable) status code");
			}
			return NOT_ACCEPTABLE_VIEW;
		}
		else {
			logger.debug("No acceptable view found; returning null");
			return null;
		}
	}

         我们看到了，是requestedMediaTypes为null引起的view为空，而requestedMediaTypes 通过getMediaTypes方法生成，看了里面的代码，才明白原来是springmvc会去判断URI的后缀，然后根据后缀去获取对应的mediatypes。jpg对应的mediatype是jpg/image。

        因此找到原因了，我们的项目中，关于springmvc的viewresolve的配置，没有关于这个media的，所以去解析视图的时候无法解析。解决办法也很简单，直接加一个默认的viewsolve就OK了。

<!--通用视图解析器-->
    <bean id="viewResolverCommon" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/WEB-INF/page/"/>  
        <property name="suffix" value=".jsp"/><!--可为空,方便实现自已的依据扩展名来选择视图解释类的逻辑  -->
        <property name="viewClass">
            <value>org.springframework.web.servlet.view.InternalResourceView</value>
        </property>
        <property name="order" value="1"/>
    </bean>