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From "Nathan Bubna" <nbu...@gmail.com>
Subject Re: Which flavor of Velocity to use?
Date Sat, 27 Dec 2008 17:11:26 GMT
On Fri, Dec 26, 2008 at 2:53 PM, Steve Cohen <scohen@javactivity.org> wrote:
> I want to try to port an existing application to Velocity.
>
> This application is in some ways quite like a Web App, yet it is not one.
>  It's user-interface is delivered through the AOL Instant Messenger SDK.  In
> AIM terms, it is a "bot".  Users chat with it as they would with any other
> AIM buddy and it performs various tasks for them, during which it presents
> them with various bits of information.
>
> AIM delivers instant messages to our bot, which is implemented using AIM's
> SDK.  An Instant Message contains of course the text of the IM, which our
> bot processes much like a command-line parser of a sort.  A properly entered
> command leads to some sort of action being performed which might be data
> retrieval or modification, or something else.  An improperly entered command
> leads to an "error page".  No matter what it is, the feedback to the user is
> an IM sent back to him via AIM.  Our bot's interface to AIM going in this
> direction is again the AIM SDK.  This is analogous to a servlet response.
>
> Additionally, although there are alternatives, AOL's preferred mechanism for
> receiving inputs from a "bot" is that it be a limited form of xhtml - that
> is, only a restricted subset of xhtml is allowed.  Things like <b>, <br/>,
> and <font> are allowed, <table> is not.  The AIM SDK provides a way of
> converting strings to this format, but it is not required to use this API.
>
> Up until now, the relatively simple nature of this interface led me down the
> primrose path of simply taking strings as input, parsing them, running them
> through whatever process was required and spitting back out the required
> output.  I gave no thoughts to MVC.  Possible outputs were stored in a
> properties file, often with various replaceable parameters.  This was easily
> handled in java, but it's become more cumbersome as the size of this
> properties file increased.  It got way more cumbersome when I started
> needing to format the text.  I developed a clever (too clever by half)
> mechanism for formatting this text using java, but I really need to get away
> from that.  Java is doing way too much.  I would rather now have a bunch of
> little "html pages" that have the formatting on them, with the content to be
> popped in via templating.
>
> What I want is to have the various boilerplate outputs stored as velocity
> templates, in an intelligently organized directory tree structure, and use
> the velocity mechanism to merge in the live data.  Fortunately, even though
> this application isn't a WebApp, I long ago made the decision to run it
> inside of Tomcat.  Although it isn't a Web application, there are a couple
> of minor interfaces that do access the application through servlets, hence
> Tomcat.  Thus the architecture is all already there to put all the templates
> under the Web Context root.
>
> However, as I said, it ISN'T actually a web app.  It doesn't deliver content
> to users via the http request/response paradigm.  One idea for using
> velocity in this situation would be to make http://localhost:8080 calls to
> the Velocity Servlet, get the merged output, read it into a StringWriter,
> and send that on to the user.  But that doesn't feel right.  It feels like
> needless overhead.
>
> I would like to invoke Velocity like a non-webapp, through java, but read
> the templates from the Web Context as though it were a web app.  Has anyone
> done anything like that, or otherwise have helpful advice for me?

Yeah, i don't think you really need the VelocityViewServlet.  (Note
that the VelocityServlet class is deprecated).   But so long as you
are running in a webapp container like Tomcat and have access to a
ServletContext, you can use the WebappResourceLoader (from
VelocityTools 2) to load templates from your web context.  Just
remember to put the ServletContext object in your VelocityEngine (or
singleton) application attributes before you initialize it:

VelocityEngine engine = new VelocityEngine();
engine.setApplicationAttribute("javax.servlet.ServletContext",
theServletContext);
engine.init(properties);
...

> Thanks.
>
>
>
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