前端靜態資源發起請求時首先會發送一個域請求，後端通過後再次發起get、post請求

使用過濾器對域請求授權，這裡授權了一個特殊的token請求欄位，可以根據自己的業務新增請求欄位。

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;

/**
 * Servlet Filter implementation class HttpFilter
 */
public class HttpFilter implements Filter {

    /**
     * Default constructor. 
     */
    public HttpFilter() {
        // TODO Auto-generated constructor stub
    }

	/**
	 * @see Filter#destroy()
	 */
	public void destroy() {
		// TODO Auto-generated method stub
	}

	/**
	 * @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)
	 */
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
		HttpServletResponse resp=(HttpServletResponse)response;
		HttpServletRequest rep = (HttpServletRequest) request;
		resp.setHeader("Access-Control-Allow-Origin", rep.getHeader("Origin"));
		resp.setHeader("Access-Control-Allow-Methods", "POST, GET,PUT, OPTIONS, DELETE,PUT");
		resp.setHeader("Access-Control-Allow-Headers", "x-requested-with,Authorizationaccept, origin, content-type, token");
		//允許跨域請求中攜帶cookie
		resp.setHeader("Access-Control-Allow-Credentials","true");
		chain.doFilter(request, response);
	}

	/**
	 * @see Filter#init(FilterConfig)
	 */
	public void init(FilterConfig fConfig) throws ServletException {
		// TODO Auto-generated method stub
	}

}