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From André Warnier>
Subject Re: Remote Tomcat webapps bidirectional communication
Date Mon, 16 Jun 2014 15:51:36 GMT
Lmhelp1 wrote:
> Hello,
> My question is about what code to write to allow two remote Tomcat 
> webapps to communicate with one another through the Internet.
> Let me explain more precisely what I would like to do.
> (I'm just simplifying a bit the real situation).
> - I have a Tomcat webapp running on a server in England.
> - I have another Tomcat webapp running on a server in France.
> - I have a JSP inside the England webapp.
> - This JSP contains a form with two fields "First name" and "Last name".
> - I would like to send these information to the France webapp.
> - After the England form has been submitted, I can collect the 
> information "First name" and "Last name" in a servlet.
> Can you tell me what I shall do then to send these information to the 
> France webapp?
> Is it something like a "response.sendRedirect(..."?
> How does it have to be written?
> - Meantime, the France webapp needs to be able to wait for these 
> information and, when they arrive, to get them and do something with 
> them. For example store the "First name" and "Last name" in a database, 
> etc.
> What kind of a code has to be written in the France webapp?
> Is it a servlet with a "doGet()" retrieving the information "First name" 
> and "Last name"?
> - Moreover, when the France webapp has finished it's job, it needs to 
> tell the England webapp that it has finished, send it a file and some 
> information.
> So the communication has to be bidirectional.
> Can you please give me some indications on how to start dealing with 
> this? Or maybe a tutorial or an example?

This is only vaguely a Tomcat question, in the sense that :
- for receiving and processing a HTTP POST request (from a browser usually, but in your 
case it would be a Tomcat servlet or a program running somewhere else), a normal webapp is

what you need.
- for creating and sending a HTTP POST request, you will need a library that offers such 
functions, such as the HTTPClient library, found here :

There is documentation and examples available at :
Make sure you read them.

Note that any java program could use this, there is nothing special about using it within

a java servlet.
And note that when one of your servlets issues a HTTP request to another server, Tomcat 
knows absolutely nothing about it, and there is no Tomcat code involved (on the 
request-sending side).

Note also that for what you describe as the "France webapp" above, that functionality does

not necessarily need a Tomcat and a Tomcat webapp.  You could use the code of
to create a stand-alone java network server, which just listens for this particular kind 
of request, and responds by the information that you describe.
Similarly, your "England webapp" does not necessarily need to send the request to the 
France server as a HTTP request, nor expect a HTTP response.

What I believe would be the trickiest part in that kind of application, is to handle the 
various error scenarios : network down between England and France, French server down, 
French server taking a (too) long time to respond, French server returning an error, etc..

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