用户在JSP和Servlet中无法使用Session登录时出现错误消息

Question

My goal is to create an error message when user fails to log in to the system. I managed to create an error message using session.

However, when I refresh the browser, the error message is still there. It should not appear. Is there a way for me to make the error message invisible when user refresh the browser?

Below are my codes. Help will be appreciate..Thanks! :)

At login.jsp

<div class="error">
<% String e = (String) session.getAttribute("error" );
if(e != null)
{
    out.print(e); 
}%>
</div>

At Servlet

HttpSession session = request.getSession(true);
session.setAttribute( "error", "Invalid username or password");
RequestDispatcher dispatcher = request.getRequestDispatcher("/login.jsp");
dispatcher.forward( request, response); 

Answer 1

Session attributes live for the duration of an HttpSession . Try using request attributes

request.setAttribute( "error", "Invalid username or password");

which only last for the duration of the request.

Otherwise, you will have to remove the attribute from the HttpSession .

Answer 2

you can either the use the request object or you can just check if the session attribute exists in the session and if so you can just remove that.

ie jsp

<% String e = (String) session.getAttribute("error" );
if(e != null)
{
    out.print(e); 
}else{
  out.print("All Is Well");
}>

servlet

HttpSession session = req.getSession(true);
    try{
        if(null != (session.getAttribute("error"))){
            session.removeAttribute("error");
        }else{
            session.setAttribute( "error", "Invalid username or password");
        }
    }catch(Exception er){
        er.printStackTrace();
    }

    RequestDispatcher dispatcher = req.getRequestDispatcher("/jsp/LoginTest.jsp");
    dispatcher.forward( req, res);