如何用Filter实现对注册用户是否登录的过滤

package filter;
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.* ;
public class UserFilter implements Filter
{

public void init(FilterConfig filterConfig) throws ServletException
{

}

public void doFilter(ServletRequest request,
            ServletResponse response,
            FilterChain chain) throws ServletException,IOException
{
response.setContentType("text/html ;charset=UTF-8");
request.setCharacterEncoding("UTF-8");
PrintWriter out=response.getWriter();

HttpServletRequest req=(HttpServletRequest)request;
HttpSession session=req.getSession();
//System.out.println(session.getAttribute("user"));

if(session.getAttribute("user")!=null){
   RequestDispatcher rd = null;
   rd = request.getRequestDispatcher("/index.jsp"); //定向的页面
   rd.forward(request, response);
}
else{
   RequestDispatcher rd = null;
   rd = request.getRequestDispatcher("/login.jsp"); //定向的页面
   rd.forward(request, response);

}
}
public void destroy(){}
}

作者“TxjDsk”

补充：软件开发 , Java ,