Is this possible --> The servlet itselt has to update all its clients

the client would need to refresh.
You can specify an auto refresh in the meta tags

tnx for ur reply tbone

I state my problem some more clearly here

Im using a servlet and this servlet generates a HTML page. say the value of varable 'int a' ('a' is zero,initially) is displayed in that HTML page.
like  out.println(value of a is + a);

The value of 'a'  is incremented,when ever a request is received by the servlet.
like a++;

that  HTML page has a button named "update",by clicking that button, a request is sent to the servlet.

in this case the servlet is accessed from three different machines.

if update button is clicked in one page,then the increment of  value 'a' has to be reflected in all three pages in three different machines.(usually only the page which calls the servlet,will be updated)

This must not be done by , refreshing the page manually or at certain intervals, or by sending a request to the servlet at certain intervals.
The servlet itselt has to update all its client pages.

Traditionally, you do not have control of the user's browser BUT you may be able to embed a tiny (1 pixel by 1 pixed) java applet in there which can be notified of the event and then tell the browser to refresh.

but in that case also, only one page can be refreshed.because of the event.
its not possible to inform all the pages in different machines to update..

Hi Object

tnx for ur suggestion.

but i need to refresh the page ,only if the value in the servlet has been changed,not for every X seconds

You can definitely have something within each applet listening for notification from the server to do a refresh.  You might have to do some socket stuff, but it can definitely be done (say open a ServerSocket within each applet that gets loaded, relay the location of the ServerSocket back to the server, and finally have the server send out a message to each of these ServerSockets that it needs to have the browser refreshed).  NOTE: I have never had the need to do this but I'm just brainstorming with you.  Anyway, this would be one way of getting the users to have their pages refreshed without their intervention.

> but i need to refresh the page ,only if the value in the servlet has been changed,not for every X seconds

if you're only using html then I can't think of another way.

you would probably need a push technology based architecture... your servlets needs to push data/events to the clients... since the HTTP is connection less protocol the servlet cannot keep track of which clients are open... you can check out the following tutorial on using Pushlets for your requirement... you can do it either with Servlets/DHTML

http://www.javaworld.com/javaworld/jw-03-2000/jw-03-pushlet_p.html


http://www.unix.org.ua/orelly/java-ent/servlet/ch06_03.htm

http://www.theserverside.com/patterns/thread.tss?thread_id=22143