springMVC拦截器返回错误信息给前端

springMVC拦截器的preHandle方法返回值是Boolean类型，所以条件够就放行，执行方法，而条件不足，前端无法知道是什么原因而被拦截，下面来解决这个问题。

一. 编写一个拦截器（该拦截器作用是：判断用户是否登录并且权限是否足够）

package com.mmall.controller.common.intercept;

import com.mmall.common.Constants;
import com.mmall.common.ResponseCode;
import com.mmall.common.ServerResponse;
import com.mmall.pojo.User;
import com.mmall.util.JsonUtil;
import lombok.extern.slf4j.Slf4j;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.PrintWriter;

/**
 * @author Luyue
 * @date 2018/8/17 18:02
 **/
@Slf4j
public class AuthorityTestIntercepter implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        HttpSession session = request.getSession();
        User user = (User) session.getAttribute(Constants.CURRENT_USER);
        if (user == null || user.getRole().intValue() != Constants.ROLE.ROLE_ADMIN) {
            return false;
        }

        log.info("preHandle");
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {

    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {

    }
}

二. 注册该拦截器

具体拦截路径可以自行更改

三. 更改拦截器，返回信息给前端

不改变之前：什么信息都没有

更改拦截器:

public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
    HttpSession session = request.getSession();
    User user = (User) session.getAttribute(Constants.CURRENT_USER);
    if (user == null || user.getRole().intValue() != Constants.ROLE.ROLE_ADMIN) {
        //重置response
        response.reset();
        //设置编码格式
        response.setCharacterEncoding("UTF-8");
        response.setContentType("application/json;charset=UTF-8");

        PrintWriter pw = response.getWriter();

        if (user == null) {
            pw.write(JsonUtil.objToJson(ServerResponse.createByErrorCodeAndMessage(ResponseCode.NEED_LOGIN.getCode(), "拦截器拦截，请登录")));
        } else {
            pw.write(JsonUtil.objToJson(ServerResponse.createByErrorCodeAndMessage(ResponseCode.ERROR.getCode(), "拦截器拦截，无权限操作")));
        }

        pw.flush();
        pw.close();
        return false;
    }

    log.info("preHandle");
    return true;
}

效果：

springMVC拦截器返回错误信息给前端

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