过滤Filter推断用户是否登录

WEB.XML 

<!-- 用户session的 键   sessionKEY -->
  <context-param>
    <param-name>userSessionKey</param-name>
    <param-value>USERSESSIONKEY</param-value>
  </context-param>
  <!-- 重定向的页面 -->
  <context-param>
    <param-name>rediretPage</param-name>
    <param-value>/u_member/Login.jsp</param-value>
  </context-param>
  <!-- 不须要过滤的页面 -->
  <context-param>
    <param-name>uncheckUrls</param-name>
    <param-value>/u_member/insert.jsp,/u_member/Login.jsp</param-value>
  </context-param>

Filter 过滤器代码

package go.onlineShop.filter;

import java.io.IOException;
import java.util.Arrays;
import java.util.List;

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.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet Filter implementation class IsLoginFilter
 * 推断是否登陆过滤器
 */
@WebFilter("/u_member")
public class IsLoginFilter implements Filter {

	//从xml中取值
	String uncheckUrls =null;
	String userSessionKey=null;
	String rediretPage=null;
    /**
     * Default constructor. 
     */
    public IsLoginFilter() {
        // 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 req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
		// TODO Auto-generated method stub
		//1.得到訪问路径
		HttpServletRequest request = (HttpServletRequest)req;
		HttpServletResponse response = (HttpServletResponse)res;
		String reqUrl = request.getRequestURL().toString();
		String reqURI = request.getRequestURI();
		
		String servletPath = request.getServletPath();
		
	//	String[] uncheckUrl = uncheckUrls.split(",");
		List<String> urls = Arrays.asList(uncheckUrls.split(","));
		//2.假设是属于不须要过滤的地址就直接  放行  方法结束
		if(urls.contains(servletPath)){
			chain.doFilter(request, response);
			return;
		}
		
		//3.从session中获取sessionKey相应的值。若不存在  则跳转到登陆页面
		
		Object user = request.getSession().getAttribute(userSessionKey);
		if(user==null){
			request.getRequestDispatcher(rediretPage).forward(request, response);
			return;
		}
		//4若存在 则放行；
		chain.doFilter(request, response);
	}

	/**
	 * @see Filter#init(FilterConfig)
	 */
	public void init(FilterConfig fConfig) throws ServletException {
		rediretPage=fConfig.getServletContext().getInitParameter("rediretPage");
		uncheckUrls=fConfig.getServletContext().getInitParameter("uncheckUrls");
		userSessionKey=fConfig.getServletContext().getInitParameter("userSessionKey");
	}

}

Login页面