登录过滤器

package test;

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 javax.servlet.http.HttpSession;

public class AuthFilter implements Filter {

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

    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {//读取session中保存的用户名，如果没登录就跳回登录页面
        HttpServletRequest req=(HttpServletRequest) request;
        HttpServletResponse res=(HttpServletResponse) response;
        
        HttpSession session=req.getSession(true);
        String username=(String)session.getAttribute("topname");
        if(username==null||"".equals(username)){
             res.sendRedirect("login.jsp");
        }else{
            chain.doFilter(req, res);;
        }
        
    }

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

    }

}