----- Original Message -----
From: "Craig R. McClanahan" <[EMAIL PROTECTED]>
To: "Tomcat Users List" <[EMAIL PROTECTED]>
Sent: Tuesday, January 22, 2002 1:04 PM
Subject: Re: Asynchronous messages from servlets
> On Tue, 22 Jan 2002, Ronald Wildenberg wrote:
>
> > Date: Tue, 22 Jan 2002 09:50:14 +0100
> > From: Ronald Wildenberg <[EMAIL PROTECTED]>
> > Reply-To: Tomcat Users List <[EMAIL PROTECTED]>
> > To: [EMAIL PROTECTED]
> > Subject: Asynchronous messages from servlets
> >
> > Hi,
> >
> > I have the following problem. A simple form submits data
> > to a servlet. The servlet sends a message via JMS to
> > another application (in another JVM). Once the message
> > has been sent, the 'service' method of the servlet ends.
> > After a while, say five seconds, the other application would
> > like to send back a response. How do I show this response
> > to the user?
> >
> > Since the 'service' method has finished after sending the
> > message, I have lost control over the output from the other
> > application.
> >
> > What I need is a way to push the response to the browser. I
> > would like the server to take the initiative in updating the browser
> > window, not the user. Is this possible in any way?
> >
> > Thanks in advance,
> > Ronald Wildenberg
> >
>
> There are two pieces to the answer for this kind of thing -- getting the
> data back from the other JVM (I assume you are using asynchronous JMS
> calls, right?), and displaying the data back to the user.
>
> For the first step, doing an asynchronous JMS call in the other direction
> (to a JMS receiver in the same JVM as Tomcat) could then receive the
> results, and make them available as a servlet context or session
> attribute.
>
> For the second, I've seen people set up a page that uses the meta-refresh
> capability in HTML to automatically keep sending a request every XX
> seconds. The servlet that receives this request will check to see if the
> results are back yet - if they are, they are displayed, if they are not it
> shows a "Request in Progress ... please wait" page with the meta refresh
> tag.
>
> The key thing is that you won't be able to respond on the original HTTP
> request, since that has already been sent and your service() method has
> returned.
>
> Craig
>[...]
Thanks for your info! if the processing of "asynchronous JMS calls" will be
responsed in short time by JMS-Thread, is the following(half-synchronous
way) also possible?
- use javax.servlet.ServletResponse.flushBuffer() to show a
info("please wait...") to client
- make a asynchronous JMS calls
- block this Servlet-Thread, wait for a "event" sent by JMS
- when the "event" comes, the blocking ends, then the results
are responsed to client, and the Servlet-Thread ends.
I am not sure about:
- can javax.servlet.ServletResponse.flushBuffer() always response
info to client before the Servlet-Thread ends(so the client can get
"please wait...
" info)? in my testing, it works, but some emails say that sometimes it
can not
work.
- is this half-synchronous way a good Servlet-DesignPattern if I can be sure
that the blocking will not need a long-time? or it is not good?
Thanks in advance!
Bo
Jan222002
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