Ernie V wrote:
> There's no useful purpose to such diatribe. Not everyone has access to the entire
>history of this list, nor should they be expected to examine every past post to find
>that their problem has been resolved.
The list archives of this list, and every list hosted by JavaSoft, are available to
everyone with web access at
http://archives.java.sun.com
and the instructions you receive when you sign up (as is true with many technically
oriented mailing lists) suggest that you research previous answers to your question
(in the archives, and in a variety of FAQ resources that are announced once a week)
before asking again. Doing so is fairly simple netiquette. Turn your comment around
-- why should the
hundreds or thousands of people receiving this list need to rehash the same questions
and answers over and over again?
As anyone who has read this list for more than a few weeks knows, I am more than
willing to help people understand the nuances of programming with servlets and JSP
pages. My normal response is to simply ignore such repeated queries -- but this
particular topic seems to pop up so many times that it's clear that the questioners
have not invested any time
at all to review previous discussions of this topic, or understood the nature of the
medium they are programming for.
> Besides, I don't think that this problem has been adequately addressed. The replies
>have been wide and ranging and some times of no value whatsoever.
> But no one has come to a satisfactory end.
>
Besides the no-value answers (of which there are some, on this list like any other),
there have been some substantive responses on this issue, from myself as well as other
posters, that there is *no* 100% reliable solution to this problem. And there is
nothing that servlets per se can do about this, because it is based on the nature of
the HTTP
protocol. Quite simply, there is no way to know when someone leaves because each
request stands alone. It's not like a TELNET session, where you can turn on
keep-alive packets to detect when the client goes away.
If you absolutely must have that kind of knowledge, you need to use a different
solution -- a client-server design, or a persistent applet-servlet connection, or
something else that maintains connection state. However, you are now going to have to
deal with the scalability implications of maintaining connections between the client
and the server for all
current clients. Otherwise, you need to define your application requirements in light
of the nature of the medium. Of course, you are not alone in this -- everyone else
programming on top of HTTP is in the same boat. There are techniques that work some
of the time, but not all of the time.
Craig McClanahan
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