当ajax异步跨域访问时，由于浏览器的保护机制，会导致cookie设置的jsessionId不能保存，导致下一次ajax请求时又重复生成sessionid，导致重复要求登录。

问题解决：

java端：

response.setContentType("textml;charset=UTF-8");        response.setHeader("Access-Control-Allow-Origin", request.getHeader("Origin"));        response.setHeader("Access-Control-Allow-Methods", "POST, GET, OPTIONS, DELETE");        response.setHeader("Access-Control-Max-Age", "0");        response.setHeader("Access-Control-Allow-Headers", "Origin, No-Cache, X-Requested-With, If-Modified-Since, Pragma, Last-Modified, Cache-Control, Expires, Content-Type, X-E4M-With,userId,token");        response.setHeader("Access-Control-Allow-Credentials", "true");        response.setHeader("XDomainRequestAllowed","1");
 ajax前端：
在ajax 请求是也要加相应的东西$.ajax({url:url,//加上这句话xhrFields: {           withCredentials: true       },       crossDomain: true,success:function(result){alert("test");},error:function(){}});
 参考自：http://www.cnblogs.com/renhaisong/p/6892341.html