Filter过滤登陆页面，不能跳转到登陆页面

[javadika]

所有页面在houtai文件夹里，运行任何一个页面，如果在没登陆的情况下，跳转到login.jsp页面登陆，该怎样实现呢？我把我写的代码贴出来，现在的问题是不能跳转到login.jsp页面，麻烦大家指点一下！感谢！！

----loginFilter.java-----
public class loginFilter implements Filter{
//---------------
//过滤admin管理页面
//---------------
FilterConfig config = null;
public void init(FilterConfig config)throws ServletException{
this.config = config;
}
public void doFilter(ServletRequest request,ServletResponse response,FilterChain chain)throws IOException,ServletException{
response.setContentType("text/html;charset=UTF-8");
HttpSession session = ((HttpServletRequest)request).getSession();
User user = (User)session.getAttribute("user");
//user是LoginServlet里面的
//HttpSession session = request.getSession();
//session.setAttribute("user", us.login(user));
if(user==null){
HttpServletResponse res = (HttpServletResponse) response;
HttpServletRequest req = (HttpServletRequest) request;
res.sendRedirect(req.getContextPath()+"/houtai/login.jsp");
}else{
chain.doFilter(request, response);
}
}
public void destroy() {
this.config = null;
}
}


----web.xml----
<filter>
<filter-name>loginFilter</filter-name>
<filter-class>bean.loginFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>loginFilter</filter-name>
<url-pattern>/houtai/*</url-pattern>
</filter-mapping>