check if session variable is null?

[sde]

how the heck do i check if a session variable is null?

here is the code doing the work

// login.jsp: set session var
User u = new User("sde");
session.putValue("user",u);

// header.jsp: make sure session user is valid
// this always evaluates to true
if( session.getValue("u") != null ){
  User u = (User)session.getValue("user");
}else{
  response.sendRedirect("../login.jsp");
}

// logout.jsp
session.invalidate();

after i logout, and go to any page that uses that header file, i can do: out.println(session.getValue("u"), and it prints "null"

i am not using that header file in the login or logout page.

[Belisarius]

I use the jsp:useBean tag, but what you're doing in principle should work. I'm a bit confused by "session.getValue("u")", as you did a "session.putValue("user",u)", so where the "u" comes from I'm not sure.

Here's how I do it.

<jsp:useBean id="user" class="dec.common.beans.UserBean" scope="session" />
<jsp:useBean id="error" class="dec.common.beans.ErrorBean" scope="session" />

<%
  String host = request.getServerName();
  String path = request.getRequestURI();
  if(user == null){
%>
  <jsp:forward page="/index.jsp" />
<%
  }else if(user.getUser() == null){
%>
  <jsp:forward page="/index.jsp" />
<%
  }else if(!user.getAuth()){
%>
  <jsp:forward page="/index.jsp" />
<%
  }else if(!request.isSecure()){
    response.sendRedirect(response.encodeRedirectURL("https://" + host + path))
  }
%>

[sde]

thanks again. i haven't been using tags as much as i probably should.

is using tags just good practice and meant to keep your code clean? or is there a performance difference too?

[Belisarius]

Tags are meant to be a restriction on the coder in an attempt to keep proper MVC seperation. I'm not aware of any performance difference, it's just that there are things you can do with tags at times that it's hard to emulate otherwise. For instance, the jsp:forward tag will keep the requested document in the address bar, whereas the redirect the address will change. The reason being that the jsp:forward is actually the same jsp as requested, it's just that further processing is forwarded to another jsp, whereas the redirect prompts the client to request a new document.