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From Quintin Beukes <quin...@skywalk.co.za>
Subject Re: How does the Client Container work?
Date Tue, 29 Sep 2009 10:24:53 GMT
Hey,

If you go read the JavaEE 5.0 spec regarding Application Clients, they
do specify the following:
As with all Java EE components, application clients use JNDI to look
up enterprise
beans, get access to resource managers, reference configurable parameters set at
deployment time, and so on. Application clients use the java: JNDI namespace to
access these items (see Chapter EE.5, “Resources, Naming, and Injection” for
details).

That is the closest they get to "remote". They do mention that the
method of deployment/installation on a client is implementation
specific, and it doesn't matter how they do it. So I guess my
explanation is suitable for Geronimo, and Geronimo is on spec.

It provides the authentication, and it is possible to do
authentication against a remote server by configuring the security
realm as such.

Then you setup your server and deploy your application client.
Further, any remote EJBs would be declared and defined as such, and
there you have your fully JavaEE on-spec application client.

If you think about it, this is a very logical design. Try and think of
an application client as any other EJB jar. Have you ever asked
yourself how to deploy an EJB jar in one server but have it wrapped by
"another server"? The name "Application Client" sort of makes one feel
this is a given, but it's misunderstood. Other application servers do
provide this facility, and it would definitely be a nice-to-have.

Though it's not a much used feature, and spending resources on other
things is probably more important. After all, it's not impossible to
achieve remoting. You just need to do it like you would with any other
JavaEE component.

Finally, I think the biggest motivation for an application client in
the spec was for the same reasons as providing web based applications.
A web based app is a UI into your application back ends. Just like
this an application client is a UI into your application back ends.
Both of them run inside a container, and uses whatever methods is
available to access those back ends. The spec does specify security in
the container is a requirement, so this helps out a bit with having
the client be "very standalone".

Quintin Beukes



On Tue, Sep 29, 2009 at 11:56 AM, Quintin Beukes <quintin@skywalk.co.za> wrote:
> I posted a link to the book on a new thread.
> Quintin Beukes
>
>
>
> On Tue, Sep 29, 2009 at 11:46 AM, Quintin Beukes <quintin@skywalk.co.za> wrote:
>> Then further, a book written by IBM states:
>>
>> With WASCE, the following considerations apply:
>>   Unlike other Java EE application servers, WASCE does not provide a unique
>>   Application Client container. Instead, you must install the full
>> server package
>>   if you want to run an application client.
>>   This is compliant with the Java EE specification, which does not require that
>>   you provide a unique installation process for the Application
>> Client container
>>   (the specification only requires that it exists). Also, because WASCE has a
>>   very small server footprint of around 150 MB, the net disk space
>> savings for a
>>   special Application Client container most likely outweighs the
>> realized benefit
>>   of disk space.
>>
>> It doesn't say you need to be on the same installation, but it does
>> say it needs to be deployed on a full installation. I did once try to
>> extra the client as a plugin, but failed to then install the plugin. I
>> think it's because the client is never really in a "started" state.
>> Maybe you can deploy the "server side" of the plugin? But on geronimo
>> it's 2 separate repo items. and you can't export them as a single
>> plugin.
>>
>> Further, I once tried running the appclient from a separate
>> installation, and all this achieved was port conflicts.
>>
>> From my struggles, this is what my conclusion was:
>> I don't think the application client was really meant to be a way for
>> remote clients to access the server, but rather for a local
>> application to gain the benefits of JavaEE. Any "remoting" has to
>> happen on the server layer, inside EJBs and what not.
>>
>> So you would develop your thick application client which is linked to
>> the EJBs in the server. This is why there are 2 components to the
>> application client, the server and client component. The client
>> component runs inside the thick application container, and works with
>> the server components to create a JavaEE environment for it. It's not
>> meant to directly communicate with remote EJBs as if being a remote
>> client.
>>
>> So to summarise (i'm probably repeating myself a lot here - having
>> difficulty in explaining this - hope you understand). You get 2 types
>> of JavaEE clients, thin clients and thick clients. Thin clients are
>> directly connected to the remote server via a remote InitialContext,
>> using corba/ejbd. Thick clients run inside a JavaEE environment, and
>> is connected to remote clients using traditional JavaEE "remoting"
>> techniques, such as remote EJBs. This is done inside the EJB layer.
>> The actual "application client" part is purely for wrapping the
>> application's parts inside the EE container.
>>
>> Quintin Beukes
>>
>>
>>
>> On Tue, Sep 29, 2009 at 11:31 AM, Quintin Beukes <quintin@skywalk.co.za> wrote:
>>> There is a book Apache Geronimo Development and Deployment by Aaron Mulder
>>>
>>> It states:
>>> As of Milestone 4, the client container must run from the same
>>> Geronimo installation as the server,
>>> which also means that it must be run on the same machine, using the
>>> bin/client.jar file in the
>>> server's Geronimo directory. The command line to start a J2EE
>>> application client looks like this:
>>> java -jar bin/client.jar ConfigName [arg1] [arg2] [arg3] ...
>>>
>>> I found the same problems with this, which is why I eventually ended
>>> up building my own client framework using Spring. It's not as dynamic,
>>> but I get similar features (ie. dependency injection, security, etc.).
>>>
>>> Quintin Beukes
>>>
>>>
>>>
>>> On Tue, Sep 29, 2009 at 9:17 AM, David Jencks <david_jencks@yahoo.com>
wrote:
>>>>
>>>> On Sep 28, 2009, at 11:45 PM, Juergen Weber wrote:
>>>>
>>>>>
>>>>> OK, thanks, so that is consistent to the way Weblogic server does it,
you
>>>>>
>>>>> http://download.oracle.com/docs/cd/E12840_01/wls/docs103/client/thinclient.html#wp1079680
>>>>> start the Weblogic client container  which then starts your client
>>>>> application.
>>>>>
>>>>> The Geronimo  Wiki says:
>>>>> You can run the Application Client with this command:
>>>>>
>>>>> %GERONIMO_HOME%/bin/client JEE5/EXAMPLEClient/2.1/car
>>>>>
>>>>> But how do you run the client container from a remote machine where there
>>>>> is
>>>>> no Geronimo installation?
>>>>>
>>>>> client -h shows no way to argument a Geronimo location.
>>>>
>>>> So far no one has shown enough interest in app client containers to set this
>>>> up well.  I think that you can use the "extract a server" feature to create
>>>> a geronimo assembly that contains your app client plugin and everything
>>>> needed to run it.  You could then unpack this on the remote client machine.
>>>>  This part should be easy to try out and any problems would most likely
be
>>>> minor bugs in dependencies in geronimo plugins.  This ought to work right
>>>> now.
>>>>
>>>> However, IIRC the last time I looked there was no obvious way to configure
>>>> the app client with the server IP address (or port), so it would really only
>>>> run on the same machine as the server.  I think this would be an easy thing
>>>> to change, and I think the code would be somewhere in geronimo-client.  I'm
>>>> not sure what a good way to _tell_ the app client where the server is might
>>>> be.  Any ideas?
>>>>
>>>> thanks
>>>> david jencks
>>>>
>>>>>
>>>>> Thanks,
>>>>> Juergen
>>>>>
>>>>>
>>>>> David Blevins wrote:
>>>>>>
>>>>>>
>>>>>> Right.  You boot the app client container from the command line,
the
>>>>>> app client container does all the work to setup the environment,
>>>>>> injects the required things into your main class, then calls your
main
>>>>>> method.
>>>>>>
>>>>>> For all intense purposes the app client is really like a mini-server
>>>>>> with a little Geronimo kernel and everything.
>>>>>>
>>>>>> -David
>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>> --
>>>>> View this message in context:
>>>>> http://www.nabble.com/How-does-the-Client-Container-work--tp25632603s134p25657764.html
>>>>> Sent from the Apache Geronimo - Users mailing list archive at Nabble.com.
>>>>>
>>>>
>>>>
>>>
>>
>

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