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From "Robert" <rmcint...@bull-enterprises.com>
Subject re: Basic questions
Date Fri, 10 May 2002 21:38:00 GMT
I won't repeat what Berin has said, so I will address the Struts +
Avalon question. Our soon-to-be-released product (eQ!) is being built on
top of Avalon for several components and the download demo that will be
available shortly will be a struts application. Now in that app, Struts
itself isn't really aware of Avalon, but the Action class that we use
for our script engine accesses that script engine via a
What do we have that uses Avalon? Well, our Persistence layer, XML-based
script engine, and our Struts adapter/manager are all based on the
Component framework/architecture. We use the built in JDBCConnection
pooling from Excalibur for the persistence layer and I'm investigating
using the caching and monitoring API's in Excalibur as well, for caching
collections and monitoring changes to the XML script files.
The question/answers about the access to the container are good ones,
and I'll admit that we probably don't do it 'correctly'. We have a
singleton class with a static method for getting a hold of the root
ComponentManager, which is an ExcaliburComponentManager. We did this
because we have some clients who are in a 2-tier environment with a fat
Swing client talking to a db on a server and running a JNDI process on
the client is still up for debate. If we were doing only serverside
apps, then binding the component manager to JNDI wouldn't be a bad idea,
and we may allow either one later on.
-----Original Message-----
From: Gonzalo Diethelm [mailto:gonzalo.diethelm@aditiva.com] 
Sent: Thursday, May 09, 2002 10:14 PM
To: Avalon Developers List; Avalon Developers List
Subject: Basic questions
I  have  been doing  some  reading on  Framework  and components,
trying to understand the   basic concepts  behind their   design.
I  have  some  honest  questions,  not  intended to  express  any
opinion on anything at all, just looking for answers.  In fact, I think
I know the answers to some of the questions, but I'm asking them anyway
to check my understanding.
Say I write a class with some kind of business logic:
  class Foo { public String getAnswer(String data) { ... } }
The class would in principle benefit with some of the life  cycle
abstractions in  Framework.  For  example, the  class could  need some
kind of configuration and  logging, so it could be  declared
  class Foo implements LogEnabled, Configurable { ... }
Now, I  start by  testing this  class from  a simple command line
program.  At  this point:
1. Do I  gain  anything by  having Foo  implement  LogEnabled and
2. Who  will call  the proper  configure()  method  in the class? Does
the  class  have to be  put into a  component manager?  This seems to me
to be the case, and if this is so, then it is kind of useless to have a
component "living by itself", not as part of  a component manager.  Is
this correct?
3. If the "component by  itself" does indeed not make  sense: the docos
talk about running components as stand-alone programs (such as my test
case).  In this case, the test program is  responsible for taking the
component through the life cycle, right?  In  this case, and supposing
the component will  ONLY be run  from a test program,  is  there any
value  at all  in  making this  class  a component and having it
implement Configurable?  I mean,  someone will have to call the
configure() method anyway; why not have the component call it itself
when appropriate?
The  second  scenario  is  running  this  business  logic  from a
servlet-based  application.   Under   this  scenario,  the   user
interface  is handled  with Struts;  the user  enters some  data, clicks
on  a button,  and a  Struts Action  class is reached.  At this point,
the Action class grabs the entered data and is  ready to call the
business logic component.
4. Is there any benefit in using a ComponentManager here?   After
all, the  Action class  could simply  create an  instance of Foo, pass
the parameters and grab the result, right?
5. My understanding is  that the ComponentManager at  least would
be helpful in providing some  kind of pooling of components.   If
this is the case, would the ComponentManager be a Singleton?   If
yes, who instantiates it?  Who ensures it really IS a singleton?
The Struts scenario is more  than just an hypothetic example;  it is
EXACTLY  the way  we plan  to build  our applications.  So, my last
questions are:
6.  Anybody  is  using Struts  +  Framework?   Can anybody  share
comments, hints, caveats, etc.?  For example, can you use  LogKit on the
Struts Action classes and on the Components, and have  all output
treated uniformly?  Or does Struts REQUIRE using log4j?
7. Anybody  can provide  a real  working example  of the Struts +
Framework combination?
Sorry if  the questions  seem basic  or confused,  and thanks  in
advance for any help.
Gonzalo A. Diethelm
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