public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {  
        // ΢żǩ  
        String signature = request.getParameter("signature");  
        // ʱ  
        String timestamp = request.getParameter("timestamp");  
        //   
        String nonce = request.getParameter("nonce");  
        // ַ  
        String echostr = request.getParameter("echostr");  
  
        PrintWriter out = response.getWriter();  
        // ͨsignatureУ飬Уɹԭechostrʾɹʧ  
        if (SignUtil.checkSignature(signature, timestamp, nonce)) {  
            out.print(echostr);  
        }  
        out.close();  
        out = null;  
    }