ajax访问jeesite session超时时返回 json

项目中 用jeesite 做服务端， ajax请求业务时，如果session超时  一直返回 web登录页面， 需要重写 shiro拦截器的onAccessDenied方法，判断到如果 Principal为空并且是ajax请求 直接ajax返回，

/** * Copyright &copy; 2012-2016 <a href="https://github.com/thinkgem/jeesite">JeeSite</a> All rights reserved. */package com.thinkgem.jeesite.modules.sys.security;import java.util.HashMap;import java.util.Map;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import org.apache.shiro.authc.AuthenticationException;import org.apache.shiro.authc.AuthenticationToken;import org.apache.shiro.authc.IncorrectCredentialsException;import org.apache.shiro.authc.UnknownAccountException;import org.apache.shiro.subject.Subject;import org.apache.shiro.web.util.WebUtils;import org.springframework.stereotype.Service;import com.thinkgem.jeesite.common.mapper.JsonMapper;import com.thinkgem.jeesite.common.utils.StringUtils;/** * 表单验证（包含验证码）过滤类 * @author ThinkGem * @version 2014-5-19 */@Servicepublic class FormAuthenticationFilter extends org.apache.shiro.web.filter.authc.FormAuthenticationFilter {public static final String DEFAULT_CAPTCHA_PARAM = "validateCode";public static final String DEFAULT_MOBILE_PARAM = "mobileLogin";public static final String DEFAULT_MESSAGE_PARAM = "message";private String captchaParam = DEFAULT_CAPTCHA_PARAM;private String mobileLoginParam = DEFAULT_MOBILE_PARAM;private String messageParam = DEFAULT_MESSAGE_PARAM;boolean isAjax(HttpServletRequest request){        return  (request.getHeader("X-Requested-With") != null  && "XMLHttpRequest".equals( request.getHeader("X-Requested-With").toString())   ) ;    }/** * 重写该方法  session超时 ajax请求 返回json  */@Overrideprotected boolean onAccessDenied(ServletRequest request, ServletResponse response) throws Exception {// TODO Auto-generated method stubHttpServletRequest httpRequest = (HttpServletRequest) request;          HttpServletResponse httpResponse = (HttpServletResponse) response;                  Subject subject = getSubject(request, response);                 if (subject.getPrincipal() == null && isAjax(httpRequest)) {         httpResponse.reset();        httpResponse.setContentType("application/json");        httpResponse.setCharacterEncoding("utf-8");        Map<String, String> map = new HashMap<String, String>();        map.put("code", "-1");        map.put("msg", "session timeOut");        httpResponse.getWriter().print(JsonMapper.toJsonString(map));    return false;        }return super.onAccessDenied(request, response);}protected AuthenticationToken createToken(ServletRequest request, ServletResponse response) {String username = getUsername(request);String password = getPassword(request);if (password==null){password = "";}boolean rememberMe = isRememberMe(request);String host = StringUtils.getRemoteAddr((HttpServletRequest)request);String captcha = getCaptcha(request);boolean mobile = isMobileLogin(request);return new UsernamePasswordToken(username, password.toCharArray(), rememberMe, host, captcha, mobile);}/** * 获取登录用户名 */protected String getUsername(ServletRequest request, ServletResponse response) {String username = super.getUsername(request);if (StringUtils.isBlank(username)){username = StringUtils.toString(request.getAttribute(getUsernameParam()), StringUtils.EMPTY);}return username;}/** * 获取登录密码 */@Overrideprotected String getPassword(ServletRequest request) {String password = super.getPassword(request);if (StringUtils.isBlank(password)){password = StringUtils.toString(request.getAttribute(getPasswordParam()), StringUtils.EMPTY);}return password;}/** * 获取记住我 */@Overrideprotected boolean isRememberMe(ServletRequest request) {String isRememberMe = WebUtils.getCleanParam(request, getRememberMeParam());if (StringUtils.isBlank(isRememberMe)){isRememberMe = StringUtils.toString(request.getAttribute(getRememberMeParam()), StringUtils.EMPTY);}return StringUtils.toBoolean(isRememberMe);}public String getCaptchaParam() {return captchaParam;}protected String getCaptcha(ServletRequest request) {return WebUtils.getCleanParam(request, getCaptchaParam());}public String getMobileLoginParam() {return mobileLoginParam;}protected boolean isMobileLogin(ServletRequest request) {        return WebUtils.isTrue(request, getMobileLoginParam());    }public String getMessageParam() {return messageParam;}/** * 登录成功之后跳转URL */public String getSuccessUrl() {return super.getSuccessUrl();}@Overrideprotected void issueSuccessRedirect(ServletRequest request,ServletResponse response) throws Exception {//Principal p = UserUtils.getPrincipal();//if (p != null && !p.isMobileLogin()){ WebUtils.issueRedirect(request, response, getSuccessUrl(), null, true);//}else{//super.issueSuccessRedirect(request, response);//}}/** * 登录失败调用事件 */@Overrideprotected boolean onLoginFailure(AuthenticationToken token,AuthenticationException e, ServletRequest request, ServletResponse response) {String className = e.getClass().getName(), message = "";if (IncorrectCredentialsException.class.getName().equals(className)|| UnknownAccountException.class.getName().equals(className)){message = "用户或密码错误, 请重试.";}else if (e.getMessage() != null && StringUtils.startsWith(e.getMessage(), "msg:")){message = StringUtils.replace(e.getMessage(), "msg:", "");}else{message = "系统出现点问题，请稍后再试！";e.printStackTrace(); // 输出到控制台}        request.setAttribute(getFailureKeyAttribute(), className);        request.setAttribute(getMessageParam(), message);        return true;}}