Webpage doesn't show new entries after saving it. Only appears after refreshing

Question

I have a JSP page that shows a list of new entries inserted on the system.

My myApplication.jsp is structured like this:

A list of entries in the system
A form with textboxes that submits new entries.

When my JSP submits, it calls my servlet class that does:

public void doPost(HttpServletRequest req, HttpServletResponse resp)
        throws IOException {
    String author = checkNull(req.getParameter("author"));
    String service = checkNull(req.getParameter("service"));
    Dao.INSTANCE.add(author, service);
    resp.sendRedirect("/myApplication.jsp");
}

My Dao.Add looks like this:

public void add(String author,String service) {
    synchronized (this) {
        EntityManager em = EMFService.get().createEntityManager();
        Shortly shortly = new Shortly(author, service);
        em.persist(shortly);
        em.close();
    }
}

The problem that I'm having is that when I get redirected back into myApplication.jsp, the list does not show the new entry I added. When I refresh the page, then it shows.

I added: And still the same issue... Sometimes I need to refresh twice for the new line to appear. — andydev, May 01 '12 at 03:08
still sounds like a caching issue, but perhaps it isn't. if it is a caching problem then perhaps you could manually clear your cache before loading the page. or use a browser add on to clear the cache. — botbot, May 01 '12 at 03:16
Check this question: http://stackoverflow.com/questions/2705008/app-engine-no-cache-jsp — Moritz Petersen, May 01 '12 at 11:34
Thanks Moritz, I followed that thread and implemented a Filter, but I still have the problem: http://i50.tinypic.com/244obv5.png Might it be related that I'm running it on my localhost? I will try to deploy it later to Google Apps and see if the problem still exists — andydev, May 02 '12 at 00:47

score 1 · Answer 1 · answered May 01 '12 at 04:39

1

If you are using IE (or even some other browsers), try putting a random number (like a timestamp ) as a parameter in your redirect code piece:

 resp.sendRedirect("/myApplication.jsp?t="+timestamp);

IE is notorious in such scenarios and due to heavy caching, things don't always work the way expect. This timestamp will indicate the browser not to show a cached page and will always (hopefully) fetch the page from the server afresh.

answered May 01 '12 at 04:39

trishulpani

744
8
20

Tried your suggestion on IE and Chrome and the same problem happens. I have a feeling is related to JSP persistence on Google App Engine – andydev May 01 '12 at 05:16

andydev · Accepted Answer · 2012-05-02T03:33:58.420

I have found that the problem is around how Google App Engine's High Replication Datastore (HDR) is designed. HDR can only guarantee Eventual consistency results.

I have found more info here

The way I proved that's the reason why I'm seeing differences, is by counting the records on the persistence, straight after adding the record.

public void doPost(HttpServletRequest req, HttpServletResponse resp)
        throws IOException {
    String author = checkNull(req.getParameter("author"));
    String service = checkNull(req.getParameter("service"));
    Dao.INSTANCE.add(author, service);
    List shortlys = new ArrayList();
    shortlys = Dao.INSTANCE.getShortlys("default");
    System.out.println("Shortlys count is: " + shortlys.size());
    resp.sendRedirect("/myApplication.jsp");
}

Several times, the output didn't increased the count, and sometimes it increased by two (the old record, and the new record added...)

Webpage doesn't show new entries after saving it. Only appears after refreshing

2 Answers2