根据浏览器的保护规则，跨域的时候我们创建的sessionId是不会被浏览器保存下来的，这样，当我们在进行跨域访问的时候，我们的sessionId就不会被保存下来，也就是说，每一次的请求，服务器就会以为是一个新的人，而不是同一个人，为了解决这样的办法，下面这种方法可以解决这种跨域的办法。

1、写一个filter并在web.xml中注册

package com.baidu.filter;

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;

public class CrosFilter implements Filter{

	@Override
	public void destroy() {
		// TODO Auto-generated method stub
		
	}

	@Override
	public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletResponse res = (HttpServletResponse) servletResponse;
        HttpServletRequest request=(HttpServletRequest)servletRequest;
        res.setContentType("textml;charset=UTF-8");
        res.setHeader("Access-Control-Allow-Origin", request.getHeader("Origin"));
        res.setHeader("Access-Control-Allow-Methods", "POST, GET, OPTIONS, DELETE");
        res.setHeader("Access-Control-Max-Age", "0");
        res.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");
        res.setHeader("Access-Control-Allow-Credentials", "true");
        res.setHeader("XDomainRequestAllowed","1");
        filterChain.doFilter(servletRequest,servletResponse);
    }

	@Override
	public void init(FilterConfig arg0) throws ServletException {
		// TODO Auto-generated method stub
		
	}

}