用户登入验证

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException,
			ServletException {

		HttpServletRequest hr = (HttpServletRequest) request;
		HttpServletResponse hs = (HttpServletResponse) response;
		HttpSession session = hr.getSession();
		User user = (User) session.getAttribute("currUser");

		if (user != null) {  //首先判断session中有没有用户
			chain.doFilter(request, response);
		} else if (hr.getServletPath().equals("/user")   //登入页要放行
                              || hr.getServletPath().equals("/") 
				|| hr.getRequestURI().contains("resources")) {  //静态资源要放行（js，css等）
			chain.doFilter(request, response);
		} else {//跳到登入页
			request.getRequestDispatcher("/").forward(request, response);
		}
	}