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From "Craig R. McClanahan" <craig...@apache.org>
Subject Re: Embedding Tomcat with intra-app Servlets
Date Fri, 02 Nov 2001 21:08:28 GMT


On Fri, 2 Nov 2001, Todd Wright wrote:

> Date: Fri, 2 Nov 2001 15:56:44 -0400
> From: Todd Wright <twright@bbn.com>
> Reply-To: Tomcat Users List <tomcat-user@jakarta.apache.org>
> To: Tomcat Users List <tomcat-user@jakarta.apache.org>
> Subject: Re: Embedding Tomcat with intra-app Servlets
>
>
> I'm not sure this solves my problem...
>
> If I pull my Servlet out of my application's code then the instance will be
> constructed and loaded by Tomcat as usual, but then the Servlet can't access
> my application's internal data.  I need the Servlet to have a callback into
> my application for it to obtain the data required for generating the response.
>

What's wrong with passing the relevant stuff with static variables?  If
your application classes are visible to webapps (by virtue of being in the
"lib" directory), these static variables and all the correpsonding classes
are visible to both.

> As a more complex example, imagine creating an HTTP front-end to, say, a
> Java-based text editor.  For the Servlet to see what's happening within the
> editor -- which file is being edited, where's the cursor, etc --it'll need
> direct access the editor's data structures.  Spilling and updating this data
> to a shared file/database/whatever would be wasteful; in my intended
> application there's 100+ megs of constantly changing data that the Servlet
> may need to examine when generating its response.
>

It's your app, so architect it the way you want ... but I would do it
differently (essentially backwards from the way you are looking at it).
I would start by designing a standard web application in which your
application logic is embedded.  Then, the only issue becomes, how do I
start the web container up when I needed it?  That's easy to manage, using
either Bootstrap.main() or the embedded class.

> Todd
>

Craig



> On Friday 02 November 2001 14:10, Craig R. McClanahan wrote:
> > Here's the Tomcat 4 approach -- 3.x has similar things but I'm not as
> > familiar with the details.
> >
> > You have two fundamental choices, based on whether you want to use
> > server.xml to configure Tomcat or not:
> >
> > * To use server.xml, you just need to set up an environment
> >   like the "catalina.sh" script does, and call
> >
> >     Bootstrap.main("start");
> >
> >   in a separate thread.  When you ultimately want to shut things
> >   down, call:
> >
> >     Bootstrap.main("stop");
> >
> > * To configure all the components yourself, you will use the
> >   org.apache.catalina.startup.Embedded class (similar to
> >   EmbeddedTomcat in 3.x).  This class includes a dummy main()
> >   program that demonstrates how you do things.
> >
> > For actually processing the requests yourself, you would only need a
> > single webapp (the ROOT webapp) with a web.xml that configures your
> > servlet to handle all requests (i.e. a <servlet-mapping> with a pattern of
> > "/*").  There's no need for interceptors (3.x) or valves (4.x) to do this.
> >
> > I would recommend you implement the application logic as a standard
> > servlet, in its own class, and separate the startup/shutdown issues out to
> > their own class.  There is nothing to be gained by combining them.
> >
> > Craig
> >
> > On Fri, 2 Nov 2001, Todd Wright wrote:
> > > Date: Fri, 2 Nov 2001 12:25:23 -0400
> > > From: Todd Wright <twright@bbn.com>
> > > Reply-To: Tomcat Users List <tomcat-user@jakarta.apache.org>
> > > To: tomcat-user@jakarta.apache.org
> > > Subject: Embedding Tomcat with intra-app Servlets
> > >
> > >
> > > I'd like to embed Tomcat within my Java application, but where some
> > > Servlet requests would *directly* call into my running application's code
> > > (+data). The current "EmbededTomcat" support seems to be aimed at
> > > launching a stand-alone Tomcat that only supports file contexts, with no
> > > callback support for access to the launching application.
> > >
> > > I'm thinking of Tomcat 3.3, 'though 4.0 could be used if required.
> > >
> > > For example, suppose I have a calendar application that I'd like to add
> > > web support.  Inside my application I have all the data I need, and I'd
> > > like my servlets to directly access my the data structures.  Flattening
> > > the data out to an external database/filesystem is not an option.  All
> > > Servlet requests would funnel into my application so I can call my own
> > > (inner) Servlet.   I still want Tomcat to do the HTTP parsing, SSL,
> > > sessions, Servlet-API, etc. My application must load the internal Servlet
> > > instance.
> > >
> > > Can I use an interceptor, or (if needed) pull apart "EmbededTomcat"?  Is
> > > there an example of how to do this?  I hope it's clear why this would be
> > > a very useful embedding scenario...
> > >
> > > Pseudocode:
> > >
> > >     public class MyApp implements Runnable {
> > >
> > >        /** launcher */
> > >        public static void main(String[] args) {
> > >            // launch!
> > >           (new MyApp()).run();
> > >        }
> > >
> > >        public void run() {
> > >           // create my internal Servlet before Tomcat is launched
> > >           //
> > >           // this inner class is defined later in this method
> > >           Servlet myServlet = new MyServlet();
> > >
> > >           // launch Tomcat
> > >           EmbeddedTomcat et = new EmbeddedTomcat();
> > >           et.setArgs(new String[] {"start"});
> > >           et.execute();
> > >
> > >           //
> > >           // hand-waving here!   Could be moved to before the
> > > "et.execute()". //
> > >           insert myServlet into Tomcat to handle all "/*" requests
> > >
> > >           //
> > >           //  I now want "myServlet" to be called with all "/*" requests
> > >           //
> > >
> > >           // run forever in this example...
> > >        }
> > >
> > >        /**
> > >         * sample internal data method.
> > >         *
> > >         * MyServlet will call this method
> > >         */
> > >        public String getInternalString() {
> > >           return "foo";
> > >        }
> > >
> > >        /**
> > >         * My inner servlet -- has access back into "MyApp"
> > >         *  instance (non-static).
> > >         */
> > >        private class MyServlet extends HttpServlet {
> > >           public void doGet(
> > >               HttpServletRequest request,
> > >               HttpServletResponse response)
> > >                    throws IOException, ServletException  {
> > >            response.setContentType("text/html");
> > >            PrintWriter out = response.getWriter();
> > >            out.println("<html><body>Internal String is ");
> > >
> > >            // access internal MyApp method/data!
> > >            out.println(getInternalString());
> > >
> > >            out.println("</body></html>");
> > >        }
> > >     }
> > >
> > > Thanks!
> > >    Todd
> > >
> > > --
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> >
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