public class LoginCheckFilter implements Filter {private FilterConfig config=null;private String webroot=null;public void destroy() {// TODO Auto-generated method stub}@Overridepublic void doFilter(ServletRequest req, ServletResponse resp,FilterChain chain) throws IOException, ServletException {// TODO Auto-generated method stubHttpServletRequest request=(HttpServletRequest)req;HttpServletResponse response=(HttpServletResponse)resp;HttpSession session=request.getSession(false); //取得當前會話的session,沒有session也不創建session,同request.getSession()一樣String url=request.getRequestURI(); //獲取當前輸入的 /項目/當前訪問的路徑 與我們定義的路徑是否相同if(url!=null&&url.equals(webroot+"/login.jsp")&&url.equals(webroot+"/LoginServlet")){chain.doFilter(req,resp);}else{if(session==null){response.sendRedirect(webroot+"/login.jsp");}else{String user2=(String)session.getAttribute("user1");if(user2==null){response.sendRedirect(webroot+"/login.jsp");}else{chain.doFilter(request, response);}}}}@Overridepublic void init(FilterConfig config) throws ServletException {// TODO Auto-generated method stubthis.config=config;ServletContext ctx=config.getServletContext(); //獲取url  /項目名webroot=ctx.getContextPath();    //項目名}}