java.rmi.server.codebase clarification

From:

david <davidzeu@gmail.com>

Newsgroups:

comp.lang.java.programmer

Date:

Wed, 7 Oct 2009 09:44:02 -0700 (PDT)

Message-ID:

<c6ff2970-b859-4fe0-aec5-15238f61af56@f20g2000prn.googlegroups.com>

Hello Guys,

I have developed a distributed Server and client application using
RMI.
First I tested both by running those in the same machine. It worked
fine.
But when I tried to keep the server classes(and stubs) in one machine
and the client classes in another machine, and test it, I got the
following exception.

Exception at the client side,
------------<Exception starts here>--------------------------------
Client exception: java.rmi.UnmarshalException: error unmarshalling
return; nested exception is:
       java.lang.ClassNotFoundException: MyRMIServer_Stub
java.rmi.UnmarshalException: error unmarshalling return; nested
exception is:
        java.lang.ClassNotFoundException: MyRMIServer_Stub
        at sun.rmi.registry.RegistryImpl_Stub.lookup(Unknown Source)
        at Client.<init>(Client.java:71)
        at Client.main(Client.java:165)
Caused by: java.lang.ClassNotFoundException: MyRMIServer_Stub
        at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:252)
        at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:
320)
        at java.lang.Class.forName0(Native Method)
        at java.lang.Class.forName(Class.java:247)
        at sun.rmi.server.LoaderHandler.loadClass(LoaderHandler.java:
434)
        at sun.rmi.server.LoaderHandler.loadClass(LoaderHandler.java:
165)
        at java.rmi.server.RMIClassLoader$2.loadClass
(RMIClassLoader.java:620)
        at java.rmi.server.RMIClassLoader.loadClass
(RMIClassLoader.java:247)
        at sun.rmi.server.MarshalInputStream.resolveClass
(MarshalInputStream.java:197)
        at java.io.ObjectInputStream.readNonProxyDesc
(ObjectInputStream.java:1575)
        at java.io.ObjectInputStream.readClassDesc
(ObjectInputStream.java:1496)
        at java.io.ObjectInputStream.readOrdinaryObject
(ObjectInputStream.java:1732)
        at java.io.ObjectInputStream.readObject0
(ObjectInputStream.java:1329)
        at java.io.ObjectInputStream.readObject(ObjectInputStream.java:
351)
..
..
..
------------<Exception ends here>--------------------------------

I will give my server and client implementation details.

In server, I do the following

---->Server side code<-----
Server()
{
  if (System.getSecurityManager() == null)
                            System.setSecurityManager ( new
RMISecurityManager() );

stub = (MyRMIInterface) UnicastRemoteObject.exportObject(myRMIServer,
0);
registry = LocateRegistry.getRegistry(host,port); //host is the IP
address passed, port 1099 by default
registry.bind("TestingRMIServer", stub);
}//server

---->Server side code<-----
Server IP address:192.168.2.181

user@server$echo $CLASSPATH
/home/user/server
user@server$rmiregistry & //
runs at the default port
user@server$java -Djava.security.manager -
Djava.security.policy=sec.policy -Djava.rmi.server.codebase=file:///
home/user/ Server 192.168.2.181

user@server$java -version
java version "1.6.0_12"
Java(TM) SE Runtime Environment (build 1.6.0_12-b04)
Java HotSpot(TM) Server VM (build 11.2-b01, mixed mode)

--------------------------------------------------------------------------------------------------------------------------------
In the client side, I implemented the following,

--->Client Side<----
Client
{
if (System.getSecurityManager() == null)
           System.setSecurityManager ( new RMISecurityManager() );

registry = LocateRegistry.getRegistry
(host,port); //the rmiregistry's IP address, and
the port
stub = (MyRMIInterface) registry.lookup("TestingRMIServer");
}//client

---->Client side<----

the client's IP address is :192.168.2.185
===<Client>=====
user@myclient$echo $CLASSPATH
/home/user/client
user@myclient$ java -Djava.security.manager -
Djava.security.policy=sec.policy -Djava.rmi.server.codebase=file:///
home/user/ Client 192.168.2.181 1099

user@myclient$java -version //CLIENT SIDE JAVA
VERSION
java version "1.6.0_10"
Java(TM) SE Runtime Environment (build 1.6.0_10-b33)
Java HotSpot(TM) Client VM (build 11.0-b15, mixed mode, sharing)
==<Client>=====

The sec.policy file has the following and I use the same on both
client and server sides..
---->sec.policy<----
grant{
                permission java.security.AllPermission;
    };
---->sec.policy<----

I expected the client to (locate and)download the server's stub.
But I still could not figure out why there is an exception, even after
I used the RMI security manager, passed the security policy and set
the codebase.
I feel that it should be either to do with my codebase setting(I am
not sure whether I am setting the codebase both at the server and
client. ) or to do with the JVM version (Since the JVMs at the server
and client are different versions)

i)When I set the codebase at the server side in the command line, can
I specify the -Djava.rmi.server.codebase=file:///home/user/
even though, my server stub is present in /home/user/server/ ??

ii) When I invoke the client, am I setting the codebase right, by
doing -Djava.rmi.server.codebase=file:///home/user/
iii) Should I include the IP address of the rmiregistry also as part
of the code base setting at the client side??

These server and client programs worked perfectly fine when I kept
both at the same machine and set the class path accordingly. The
machines involved are all Linux machines.

Any kind of help is appreciated. Thanks.

--david