anchor.diff:    User user = (User)session.getAttribute("user");
     if(user==null){
   %>
  +    <td> | </td>
       <td>
         <a href="<%=request.getContextPath()%>/system/register.jsp">Sign up</a>
       </td>
  +    <td> | </td>
       <td>
         <a href="<%=request.getContextPath()%>/system/login.jsp">Sign in</a>
       </td>
  
positive.code:           displayName = ((QQUser)user).getNickname();
        }
  %>
      <td>
        Welcome【<%=displayName%>】
      </td>
      <td>
        <a href="<%=request.getContextPath()+"/system/logout.jsp"%>">Sign out</a>
      </td>
  
negative.code: <%
    if(!"true".equals(request.getParameter("index"))){
  %>
      <td> | </td>
      <td>
      <a href="<%=request.getContextPath()%>/index.jsp">Home page</a> <br/>
      </td>
  