使用 SimpleMappingExceptionResolver 统一处理 spring mvc 异常

异常处理每个程序员应该都不陌生，我们项目代码在遇到一些未知的错误或者异常时，不能直接将这些错误信息直接返回到前端，展示给用户看，我们应该将这些错误转化成用户能够看得懂的简洁的错误信息。

spring mvc在统一异常处理方面提供了两种方式：一种是使用HandlerExceptionResolver接口，一种是在控制器controller内部使用@ExceptionHandler注解的方式，本篇文章主要讲解如何使用实现了HandlerExceptionResolver接口的类来统一处理spring mvc异常。

SimpleMappingExceptionResolver 提供了简单的统一异常的处理。

直接上代码

package com.ctp.ghub.exception;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.alibaba.fastjson.JSONObject;

import com.ctp.ghub.model.ErrorConstant;
import com.ctp.ghub.model.Result;
import org.apache.log4j.Logger;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.handler.SimpleMappingExceptionResolver;

/**
 * @author chengtianping
 * @description Spring MVC 异常处理
 * 两种处理机制
 * 1. 直接实现自己的HandlerExceptionResolver，
 * 当然这也包括使用Spring已经为我们提供好的SimpleMappingExceptionResolver和DefaultHandlerExceptionResolver
 * 2. 使用注解的方式实现一个专门用于处理异常的Controller——ExceptionHandler
 * @date 2018/5/21
 */
public class SpringGlobalExceptionHandler extends SimpleMappingExceptionResolver {

    private static Logger log = Logger.getLogger(SpringGlobalExceptionHandler.class);

    public static final String UTF_8 = "utf-8";
    public static final String ACCEPT = "accept";
    public static final String APPLICATION_JSON = "application/json";
    public static final String X_REQUESTED_WITH = "X-Requested-With";
    public static final String XML_HTTP_REQUEST = "XMLHttpRequest";
    public static final String APPLICATION_JSON_CHARSET_UTF_8 = "application/json; charset=utf-8";

    @Override
    public ModelAndView doResolveException(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse,
                                         Object o, Exception ex) {
        ModelAndView modelAndView;
        httpServletResponse.setCharacterEncoding(UTF_8);
        String viewName = determineViewName(ex,httpServletRequest);
        String accept = httpServletRequest.getHeader(ACCEPT);
        boolean isJsonXMLRequest = accept != null && !(accept.indexOf(APPLICATION_JSON) != -1
            || (httpServletRequest.getHeader(X_REQUESTED_WITH) != null
            && httpServletRequest.getHeader(X_REQUESTED_WITH).indexOf(XML_HTTP_REQUEST) != -1));
        if (!isJsonXMLRequest) {
            //非 json xml ajax 请求 返回正常的视图
            Integer statusCode = determineStatusCode(httpServletRequest, viewName);
            if (statusCode != null) {
                applyStatusCodeIfPossible(httpServletRequest, httpServletResponse, statusCode);
             }
            modelAndView = getModelAndView(viewName, ex, httpServletRequest);
        } else {
            PrintWriter writer = null;
            try {
                //json xml 请求 ajax请求 返回json格式的错误信息
                // json 请求返回
                httpServletResponse.setContentType(APPLICATION_JSON_CHARSET_UTF_8);
                writer = httpServletResponse.getWriter();
                Result<String> result = Result.createFailResult(ErrorConstant.SYS_ERR);
                writer.write(JSONObject.toJSONString(result));
                writer.flush();
            } catch (IOException e) {
                if (log.isInfoEnabled()) {
                    logger.error("SpringGlobalExceptionHandler exception  ",e);
                }
            }finally{
                if(null != writer){
                    writer.flush();
                    writer.close();
                }
            }
            return null;
        }
        return modelAndView;
    }
}

如果是普通请求则返回响应的视图，如果是ajax请求，则返回封装好的json格式的错误信息，再由前端去展示

在spring-servlet.xml中需要配置统一异常的bean,让spring 容器去统一管理