SpringMVC错误页面配置

当前SpringMVC非常流行，在大多数情况，我们都需要自定义一些错误页面（例如：401， 402， 403， 500…），以便更友好的提示。对于spring mvc，这些当然是支持自定义的，spring是怎么做的？ 还是去看看spring的源码吧：

原理

DispatcherServlet

众所周知，springmvc的入口是DispatcherServlet, 在DispatcherServlet的源码中，不知你是否注意到了以下方法：

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()) {
            request.setAttribute(EXCEPTION_ATTRIBUTE, ex);
            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;
}

这个方法就是springmvc对于异常的处理，其调用了HandlerExceptionResolver的resolveException方法。HandlerExceptionResolver有众多实现类，其中，重点看看
SimpleMappingExceptionResolver（我们就是要通过它来配置自定义错误页面）。

SimpleMappingExceptionResolver

public class SimpleMappingExceptionResolver extends AbstractHandlerExceptionResolver {
    ...
    private Properties exceptionMappings;

    private Class<?>[] excludedExceptions;

    private Map<String, Integer> statusCodes = new HashMap<String, Integer>();
    ...

    public void setExceptionMappings(Properties mappings) {
        this.exceptionMappings = mappings;
    }

    public void setStatusCodes(Properties statusCodes) {
        for (Enumeration<?> enumeration = statusCodes.propertyNames(); enumeration.hasMoreElements();) {
            String viewName = (String) enumeration.nextElement();
            Integer statusCode = new Integer(statusCodes.getProperty(viewName));
            this.statusCodes.put(viewName, statusCode);
        }
    }

}

@Override
protected ModelAndView doResolveException(HttpServletRequest request, HttpServletResponse response,
        Object handler, Exception ex) {

    // Expose ModelAndView for chosen error view.
    String viewName = determineViewName(ex, request);
    if (viewName != null) {
        // Apply HTTP status code for error views, if specified.
        // Only apply it if we're processing a top-level request.
        Integer statusCode = determineStatusCode(request, viewName);
        if (statusCode != null) {
            applyStatusCodeIfPossible(request, response, statusCode);
        }
        return getModelAndView(viewName, ex, request);
    }
    else {
        return null;
    }
}

protected String determineViewName(Exception ex, HttpServletRequest request) {
    String viewName = null;
    if (this.excludedExceptions != null) {
        for (Class<?> excludedEx : this.excludedExceptions) {
            if (excludedEx.equals(ex.getClass())) {
                return null;
            }
        }
    }
    // Check for specific exception mappings.
    if (this.exceptionMappings != null) {
        viewName = findMatchingViewName(this.exceptionMappings, ex);
    }
    // Return default error view else, if defined.
    if (viewName == null && this.defaultErrorView != null) {
        if (logger.isDebugEnabled()) {
            logger.debug("Resolving to default view '" + this.defaultErrorView + "' for exception of type [" +
                    ex.getClass().getName() + "]");
        }
        viewName = this.defaultErrorView;
    }
    return viewName;
}

protected String findMatchingViewName(Properties exceptionMappings, Exception ex) {
    String viewName = null;
    String dominantMapping = null;
    int deepest = Integer.MAX_VALUE;
    for (Enumeration<?> names = exceptionMappings.propertyNames(); names.hasMoreElements();) {
        String exceptionMapping = (String) names.nextElement();
        int depth = getDepth(exceptionMapping, ex);
        if (depth >= 0 && (depth < deepest || (depth == deepest &&
                dominantMapping != null && exceptionMapping.length() > dominantMapping.length()))) {
            deepest = depth;
            dominantMapping = exceptionMapping;
            viewName = exceptionMappings.getProperty(exceptionMapping);
        }
    }
    if (viewName != null && logger.isDebugEnabled()) {
        logger.debug("Resolving to view '" + viewName + "' for exception of type [" + ex.getClass().getName() +
                "], based on exception mapping [" + dominantMapping + "]");
    }
    return viewName;
}

protected Integer determineStatusCode(HttpServletRequest request, String viewName) {
    if (this.statusCodes.containsKey(viewName)) {
        return this.statusCodes.get(viewName);
    }
    return this.defaultStatusCode;
}

由此可见：

SimpleMappingExceptionResolver通过 exceptionMappings和statusCodes来确立Exception、http状态码以及view之间的映射关系。明白这个就很简单了，我们可以通过设置exceptionMappings、statusCodes的值来实现我们自定义的映射关系。

实战

页面准备

1. 我们在WEB-INF/views/commons/error（目录自己定）新建我们自定义的错误页面，404.html, 500.html等等。

2. SimpleMappingExceptionResolver只实现映射关系，我们还需要通过配置web.xml来实现。

   <error-page>
       <error-code>404</error-code>
       <location>/error/404.html</location>
   </error-page>
   
   <error-page>
       <error-code>500</error-code>
       <location>/error/500.html</location>
   </error-page>

    

    

3. 在spring-mvc配置文件中将404.html、500.html等设置为资源文件，避免被springmvc再次拦截。

   <mvc:resources mapping="/error/**" location="/WEB-INF/views/commons/error/" />

4. 配置SimpleMappingExceptionResolver。

   <bean class="org.springframework.web.servlet.handler. SimpleMappingExceptionResolver">
       <property name="exceptionMappings">
           <map>
               <entry key="ResourceNotFoundException" value="common/error/resourceNotFoundError" />
               <entry key=".DataAccessException" value="common/error/dataAccessError" />
           </map>
       </property>
       <property name="statusCodes">
           <map>
               <entry key="common/error/resourceNotFoundError" value="404" />
               <entry key="common/error/dataAccessError" value="500" />
           </map>
       </property>
   </bean>

到此，就实现我们需要的配置了。