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From "Craig R. McClanahan" <craig...@apache.org>
Subject Re: Is Struts suitable for Java client?
Date Wed, 14 Aug 2002 04:53:09 GMT


On Wed, 14 Aug 2002, John Yu wrote:

> Date: Wed, 14 Aug 2002 12:25:02 +0800
> From: John Yu <john@scioworks.com>
> Reply-To: Struts Users Mailing List <struts-user@jakarta.apache.org>
> To: Struts Users Mailing List <struts-user@jakarta.apache.org>
> Subject: Re: Is Struts suitable for Java client?
>
> You can return binary data from the Actions. In the action's
> perform()/execute(), instead of returning a forward mapping, what you can
> do is:
>     * Set the correct content type and header by calling
> response.setContentType() and setHeader()
>     * Get the output stream from response.getOutputStream() and stream
> whatever binary data you need to return
>     * at the end of the perform()/execute() method, return null.

John is spot on in describing the mechanics of meeting this need.  A
little more background information on why Struts works this way might be
useful to you, and to others considering web "applications" that do not
emit HTML directly.

The general MVC model that Struts encourages is to have your Action
perform the business operations related to a particular request, but not
to get involved in creating the actual response.  Instead, the normal
pattern is to forward to some other resource in the webapp (typically, but
not necessarily, a JSP page).  For example, you can forward to a servlet
that produces binary output.

However, Struts does not *force* you to take this approach.  In general,
returning null from your Action.perform() or Action.execute() method says
"I have already taken care of producing the response -- there is no need
for any further processing".

Some example scenarios where this might be better than forwarding to a
different resource to produce the response content:

* Your Action decides that a redirect to some other (internal or
  external) URL is appropriate.  If the Action has called
  response.sendRedirect(), you don't need or want to have some other
  webapp resource try to create a response that isn't going to be seen
  in any event.

* Your Action is creating a dynamic image (such as the graph from a
  live stock price tracking application -- although for most stocks,
  including SUNW (my employer), I don't really want to see the recent
  graphs, thank you :-).  If your Action writes the binary data for this
  graph directly to the response, there is no need for a separate
  resource to produce it.

* Your action is creating a response stream containing a serialized
  Java object (such as when you are talking to an applet).  If your
  Action does this directly, you won't want to forward to a JSP page
  anyway -- the response has already been created.

* Your Action creates a response that is going to be transformed by a
  Filter before being returned to a client (such as the common scenario
  where your Action returns XML data that will be transformed by a Filter
  depending on what kind of client device is making the request).  This
  will be a common scenario when the business logic of your application
  wants to create XML data in some standardized format that is transformed
  into browser-specific (or wireless-device-specific) HTML or WML by an
  external filter.  (Note that you can still use a JSP page to do this
  sort of XML output with interspersed dynamic output via custom tags;
  the point is that you might be rendering the output from something like
  an XML DOM tree that is dynamically generated by your Action).

(Broad hint for a future direction for Struts -- would you like to create
Struts-based applications that can make their underlying information
available via both interactive apps as HTML, and web services using SOAP
formats?  And be interoperable with JAX-RPC?  I would like that also.
Stay tuned ...)

Craig McClanahan




> At 01:09 pm 13-08-2002, you wrote:
> >Hi all,
> >
> >     I'm going to develop a java application with java client on client side
> >which talks to a controller servlet. The data transmitted between client and
> >server may be serialized object.
> >     Does Struts support java client by outputting a serialized object as a
> >HTTP response instead of forwarding to a JSP? If yes, would anyone give me
> >some hints? Thanks.
> >
> >Best Regards,
> >Leslie
> >
> >
> >--
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>
> --
> John Yu                       Scioworks Technologies
> e: john@scioworks.com         w: +(65) 873 5989
> w: http://www.scioworks.com   m: +(65) 9782 9610
>
> Scioworks Camino - "Don't develop Struts Apps without it!"


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