Spring MVC的Controller统一异常处理：HandlerExceptionResolver

转载自：http://blog.youkuaiyun.com/xiao__gui/article/details/45422649

出现异常并不可怕，可怕的是出现了异常，你却不知道，也没有进行异常处理。 
Spring MVC的Controller出现异常的默认处理是响应一个500状态码，再把错误信息显示在页面上，如果用户看到这样的页面，一定会觉得你这个网站太LOW了。 
要解决Controller的异常问题，当然也不能在每个处理请求的方法中加上异常处理，那样太繁琐。Spring MVC提供了一个HandlerExceptionResolver接口，可用于统一异常处理。

HandlerExceptionResolver接口

<code class="language-Java hljs cs has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">interface</span> HandlerExceptionResolver {
    ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex);
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>

HandlerExceptionResolver接口中定义了一个resolveException方法，用于处理Controller中的异常。Exception ex参数即Controller抛出的异常。返回值类型是ModelAndView，可以通过这个返回值来设置异常时显示的页面。

实现HandlerExceptionResolver

HandlerExceptionResolver是一个interface，还需要定义一个实现类，来实现异常出现后的逻辑。

<code class="language-Java hljs java has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">MyExceptionResolver</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">implements</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">HandlerExceptionResolver</span> {</span>

    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> ExceptionLogDao exceptionLogDao;

    <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> ModelAndView <span class="hljs-title" style="box-sizing: border-box;">resolveException</span>(HttpServletRequest request,
            HttpServletResponse response, Object handler, Exception ex) {

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 异常处理，例如将异常信息存储到数据库</span>
        exceptionLogDao.save(ex);

        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 视图显示专门的错误页</span>
        ModelAndView modelAndView = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> ModelAndView(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"errorPage"</span>);
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> modelAndView;
    }
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li></ul>

上面代码实现了HandlerExceptionResolver类的resolveException方法。出现异常时，会将异常信息存储到数据库，并显示专门的错误页面。 
当然，还有一些其他常用的异常处理方法，例如通过javamail将异常报警发送给相关人员。总之，出现的异常要能被相关人员看到，这样才能不断完善代码。

配置

最后，还需要将自己的HandlerExceptionResolver实现类配置到Spring配置文件中，或者加上@Component注解。

<code class="language-xml hljs  has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;"><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">bean</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"com.xxg.MyExceptionResolver"</span> /></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

至此，MyExceptionResolver就可以处理Controller抛出的异常了。

相关问题

HandlerExceptionResolver和web.xml中配置的error-page会有冲突吗？

web.xml中配置error-page同样是配置出现错误时显示的页面：

<code class="language-xml hljs  has-numbering" style="display: block; padding: 0px; background: transparent; color: inherit; box-sizing: border-box; font-family: "Source Code Pro", monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal;"><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">error-page</span>></span>
    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">error-code</span>></span>500<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">error-code</span>></span>
    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">location</span>></span>/500.jsp<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">location</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">error-page</span>></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right: 1px solid rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>

如果resolveException返回了ModelAndView，会优先根据返回值中的页面来显示。不过，resolveException可以返回null，此时则展示web.xml中的error-page的500状态码配置的页面。 
当web.xml中有相应的error-page配置，则可以在实现resolveException方法时返回null。 
API文档中对返回值的解释：

return a corresponding ModelAndView to forward to, or null for default processing.