Ulises,
On Mon, Jan 19, 2004 at 07:33:11AM -0800, Ulises wrote:
> I have to read diffrent devices like sensors and alarms (by reading
> a port upd/ip and tcp/ip) and then show its status in some graphical
> form in a browser (in real time). The platform is J2EE. Does somebody
> knows or have experience to the respect?, principally architecture
> scope.
J2EE, JSP, servlets, etc, are not a good fit for this, since HTTP
is inherently a post & response "pull" technology. You can squeeze it
into J2EE, but you're better off using a constant network connection.
Before you go any further, though, you should clarify what needs
are driving the software.
For example, what do you mean by "real time". If "updated every
few minutes" is often enough for you, then a servlet or JSP should do
just fine. Just have the page use a meta refresh tag. That tells the
browser to reload the page every n seconds. For example, this causes
the page to reload every 180 seconds:
<HTML>
<HEAD>
<meta http-equiv="refresh" content="180">
</HEAD>
<BODY>
Some content
</BODY>
</HTML>
For more info, google "meta refresh", the first link that turned
up when I did was:
http://www.htmlhelp.com/reference/html40/head/meta.html
You can crank this down to reloading every second, but sooner or
later the overhead of reloading is going to be obnoxious.
If you need something much, much faster in realtime, you may want
to consider just writing an applet that listens on a port for any
change announcements.
--
Steven J. Owens
[EMAIL PROTECTED]
"I'm going to make broad, sweeping generalizations and strong,
declarative statements, because otherwise I'll be here all night and
this document will be four times longer and much less fun to read.
Take it all with a grain of salt." - Me at http://darksleep.com
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