servlet Date tracking

[Tyrone Chandler]

Hi
I wanted to know if anyone could tell me how I can put a Date or Calender object in a servlet so that it tells me how long it's been since i last visited a page? Basically I'm looking to tell the visitor the number of seconds since the last visit. Thanks so much!

[Ko Ko Naing]

Oh well... U have to maintain the users status in external database to do that... Fisrt u have to import the java.util.Calendar, develop a class that extends Calendar, implement HttpSessionBindingListener... You have to know how to do things in valueBound and valueUnbound methods of that interface(Save the date and time to the database in valueUnbound method)... Instantiate one object of them in your servlet and add to the current live session... If the session is invalidated, the valueUnbound method of your class will be called...
Actually if I believe that what I've mentioned above is not enough to do real implementation... U might need to study about the listener and session management more....
Anyway, it might helps you logically...

[Frank Carver]

That sounds an overly-complicated solution to me.
To solve this issue in a simpler way, first you need to decide what constitutes the "I" in "since I last visited the page". Have you already logged on or otherwise authenticated yourself? Is the IP address of your computer enought to identify you?
Once you have something which identifies you to the computer, the simplest way of maintaining "last accessed" information is to place a Map (such as a HashMap) in the "application" context, keyed by your used id, with each entry being a Date object.
For example, in your servlet you might have code like:

  public void doGet(HttpServletRequest req, HttpServletResponse res)
    throws ServletException, IOException
  {
    Map lastAccess = (Map)getServletContext().getAttribute("last access");
    String uid = getUserId();
    Date date;
    if (lastAccess containsKey(uid))
    {
      date = (Date)lastAccess.get(uid);
    }
    else
    {
      date = new Date();
    }
    // update the map for _this_ visit
    lastAccess.put(uid, new Date());
  }

This should work for as long as your web application is running, but the data will be lost of the application or the server stops or restarts. For a more permanent solution, you need to persist this information, typically to a file or database.

[Ko Ko Naing]

Originally posted by Frank Carver:
That sounds an overly-complicated solution to me.

I'm trying to explain... But I would be sorry, if my words make the readers complicated..... But the concept is to be notified, when a session is invalidated and save the logout time into the database...

[Frank Carver]

when a session is invalidated and save the logout time into the database
Perhaps we have different understanbdings of what theoriginal poster was asking for. I read "how long it's been since i last visited a page" as a simple need to store the last time each user visited a page. Note that this is not the same as "how long it's been since i last visited a site".
This has nothing to do with sessions - If I visit a page now, and again in two minutes time, I will still have the same session, but I want the "last accessed" data to be updated each time.
If the map of last visit dates needs to be persisted, it might either be persisted every time a date is updated using a DB, a prevalence layer, etc.), or on a scheduled basis (say once per hour or whatever).
Can you explain why you feel that session creation and expiry might affect this problem?

[Ko Ko Naing]

Originally posted by Frank Carver:
[QBPerhaps we have different understanbdings of what theoriginal poster was asking for. I read "how long it's been since i last visited a page" as a simple need to store the last time each user visited a page. Note that this is not the same as "how long it's been since i last visited a site".
If the map of last visit dates needs to be persisted, it might either be persisted every time a date is updated using a DB, a prevalence layer, etc.), or on a scheduled basis (say once per hour or whatever).
Can you explain why you feel that session creation and expiry might affect this problem?[/QB]

Yeah, I also think that I misinterpreted the original post..... I thought that the user wants to view the last time that he/she logged into the system... So I let the HttpSessionBindingListener to notify the event to the object, when his/her session is invalidated...
Of course, I now know that I misinterpret the post...
I'm sorry, Mr.Frank...