java Servlet Filter 拦截Ajax请求，统一处理session超时的问题

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.shiro.SecurityUtils;
import org.apache.shiro.subject.Subject;

import cn.zsmy.constant.Constant;
import cn.zsmy.entity.User;

/**
* session超时过滤
*
* @date 2016-10-20
*/
public class SessionFilter implements Filter {

@Override
public void init(FilterConfig filterConfig) throws ServletException {

}

@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException,
ServletException {
HttpServletRequest httpServletRequest = (HttpServletRequest) request;
HttpServletResponse httpServletResponse = (HttpServletResponse) response;

//只过滤了ajax请求时session超时
if (httpServletRequest.getHeader("x-requested-with") != null
&& httpServletRequest.getHeader("x-requested-with").equalsIgnoreCase("XMLHttpRequest")) {
Subject subject = SecurityUtils.getSubject();
User user = (User) subject.getPrincipal();
if(user == null){
Constant.MY_LOG.debug("filter：sessionstatus timeout！");
//如果是ajax请求响应头会有，x-requested-with
httpServletResponse.setHeader("sessionstatus", "timeout");//在响应头设置session状态
return;
}
}

chain.doFilter(request, response);
}

@Override
public void destroy() {

}

}

<!--session超时过滤处理 -->
<filter>
<filter-name>sessionFilter</filter-name>
<filter-class>cn.zsmy.palmdoctor.filter.SessionFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>sessionFilter</filter-name>
<!-- <url-pattern>/*</url-pattern> -->
<url-pattern>*.do</url-pattern>
</filter-mapping>

<c:set var="appPath" value="<%=request.getContextPath()%>"/>

<script type="text/javascript">
$(function(){
$.ajaxSetup ({
cache: false, //关闭AJAX缓存
async:false, //同步请求
contentType:"application/x-www-form-urlencoded;charset=utf-8",
complete:function(XMLHttpRequest,textStatus){
//通过XMLHttpRequest取得响应头，sessionstatus，
var sessionstatus=XMLHttpRequest.getResponseHeader("sessionstatus");
if(sessionstatus=="timeout"){
alert("由于您长时间未操作,登录已失效,请重新登录");
parent.location.href = "${appPath}/login.do";
}
}
});
});
</script>