RMI in Tomcat - last try

[Nikola Milutinovic <Ni...@ev.co.yu>]

Hi all.

Me and the team have given up on RMI and went to RPC, but I thought I'd 
make one last educational attempt.

Is anyone using RMI in TC where TC is acting as a RMI client to a remote 
RMI, general-purpose, server?

I have seen tons of (rather old) examples of Applet being a RMI client 
and they do not help me one bit.

To remind the group of my problems, I'll recap. I have a working RMI 
client and server packages, plus command line test client application 
which uses RMI client lib successfully against the server. When the same 
lib is used in Tomcat from a servlet, it throws ClassCastException.

Further investigation has shown that the class that Servlet gets from 
RMI subsystem implements the desired interface, to which it is being 
cast. It also showed that the classloader of the class was RMI 
ClassLoader, while other classes in the servlet, including servlet 
itself werefrom TC's ClassLoader. It lead me to believe that *that* is 
the source of the problem. It has occured to me that, since TC web 
application has several classloaders, bound into a hierarchy, maybe RMI 
classloader should be somehow introduced into it.

QUESTIONS

Am I on the right track?
If yes, how do I bind in RMI ClassLoader into TC's ClassLoader hierarchy?
And, lastly, who should do it - Servlet or RMI client?

The last question is more a design question, but it could also be a 
feasibility question, too. Can RMI client detect a classloader it should 
bind into? It could be dome from the Servlet, but I would like to have a 
general purpose Servlet that would be oblivious of underlying 
implementation.

I thought that at least JBoss developers would have something to say on 
this question, since, as I recall, JBoss uses or has been using a lot of 
RMI. There was one article or was it JBoss docs, which explained some 
problems of classloading, which were very similar to mine. I don't 
recall those docs saying anything to solve the problem in TC.

Nix.

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Re: RMI in Tomcat - last try

[Nikola Milutinovic <Ni...@ev.co.yu>]

Woodchuck wrote:

>hihi Nikola,
>
>where are you placing your JAR files?  are any in TC/commons/lib or
>TC/shared/lib?
>
>try placing everything together, just as a test.  put *all* your
>classes and JAR files under TC/commons for example and give it a try...
>they should be able to see each other if they are at the same
>classloading hierarchy level... this is what i suspect your problem is
>
>http://struts.apache.org/userGuide/configuration.html#config_add
>  
>

Hi Woodchuck.

I forgot to mention that, when I place ALL classes inside 
WEB-INF/classes, including the *_Stub classes, then it works. I guess in 
that case TC's classloader picks up the classes before RMI classloader 
and, since it is teh same CL, it works.

This solution is a patch, as far as I am concerned, since copying all 
those classes to clients classpath (TC's webapp WEB-INF/classes) is 
actually what RMI is supposed to root out. If I cannot have server 
classes in RMI codebase (one place), then I can as well go use RPC or 
pure sockets/serialization.

All of this still makes me believe that somehow RMI classloader should 
be introduced into TC's CL hierarchy. Or maybe install JBoss altogehter?

Nix.



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Re: RMI in Tomcat - last try

[Woodchuck <wo...@yahoo.com>]

hihi Nikola,

where are you placing your JAR files?  are any in TC/commons/lib or
TC/shared/lib?

try placing everything together, just as a test.  put *all* your
classes and JAR files under TC/commons for example and give it a try...
they should be able to see each other if they are at the same
classloading hierarchy level... this is what i suspect your problem is

http://struts.apache.org/userGuide/configuration.html#config_add

hth,
woodchuck


--- Nikola Milutinovic <Ni...@ev.co.yu> wrote:

> Hi all.
> 
> Me and the team have given up on RMI and went to RPC, but I thought
> I'd 
> make one last educational attempt.
> 
> Is anyone using RMI in TC where TC is acting as a RMI client to a
> remote 
> RMI, general-purpose, server?
> 
> I have seen tons of (rather old) examples of Applet being a RMI
> client 
> and they do not help me one bit.
> 
> To remind the group of my problems, I'll recap. I have a working RMI 
> client and server packages, plus command line test client application
> 
> which uses RMI client lib successfully against the server. When the
> same 
> lib is used in Tomcat from a servlet, it throws ClassCastException.
> 
> Further investigation has shown that the class that Servlet gets from
> 
> RMI subsystem implements the desired interface, to which it is being 
> cast. It also showed that the classloader of the class was RMI 
> ClassLoader, while other classes in the servlet, including servlet 
> itself werefrom TC's ClassLoader. It lead me to believe that *that*
> is 
> the source of the problem. It has occured to me that, since TC web 
> application has several classloaders, bound into a hierarchy, maybe
> RMI 
> classloader should be somehow introduced into it.
> 
> QUESTIONS
> 
> Am I on the right track?
> If yes, how do I bind in RMI ClassLoader into TC's ClassLoader
> hierarchy?
> And, lastly, who should do it - Servlet or RMI client?
> 
> The last question is more a design question, but it could also be a 
> feasibility question, too. Can RMI client detect a classloader it
> should 
> bind into? It could be dome from the Servlet, but I would like to
> have a 
> general purpose Servlet that would be oblivious of underlying 
> implementation.
> 
> I thought that at least JBoss developers would have something to say
> on 
> this question, since, as I recall, JBoss uses or has been using a lot
> of 
> RMI. There was one article or was it JBoss docs, which explained some
> 
> problems of classloading, which were very similar to mine. I don't 
> recall those docs saying anything to solve the problem in TC.
> 
> Nix.
> 
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> To unsubscribe, e-mail: tomcat-user-unsubscribe@jakarta.apache.org
> For additional commands, e-mail: tomcat-user-help@jakarta.apache.org
> 
> 



		
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