The RMI API isn't finding my classes?

[Aaron Ballard]

I'm writing a Java server application, which I have decided to make use an extra fancy distributed model using Remote Method Invocation so the different parts can talk to each other. I read a tutorial on it, wrote an application, and compiled it. Everything worked up until I ran the part of the server that contained the RMI server code.

It seemed to be starting up properly, then died in a glorious puff of stack trace:

Exception in thread "main" java.rmi.ServerException: RemoteException occurred in
 server thread; nested exception is:
        java.rmi.UnmarshalException: error unmarshalling arguments; nested excep
tion is:
        java.lang.ClassNotFoundException: LoginServer
        at sun.rmi.server.UnicastServerRef.oldDispatch(Unknown Source)
        at sun.rmi.server.UnicastServerRef.dispatch(Unknown Source)
        at sun.rmi.transport.Transport$1.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at sun.rmi.transport.Transport.serviceCall(Unknown Source)
        at sun.rmi.transport.tcp.TCPTransport.handleMessages(Unknown Source)
        at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(Unknown Sou
rce)
        at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(Unknown Sour
ce)
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source
)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)
        at sun.rmi.transport.StreamRemoteCall.exceptionReceivedFromServer(Unknow
n Source)
        at sun.rmi.transport.StreamRemoteCall.executeCall(Unknown Source)
        at sun.rmi.server.UnicastRef.invoke(Unknown Source)
        at sun.rmi.registry.RegistryImpl_Stub.bind(Unknown Source)
        at java.rmi.Naming.bind(Unknown Source)
        at Server.main(Server.java:49)
Caused by: java.rmi.UnmarshalException: error unmarshalling arguments; nested ex
ception is:
        java.lang.ClassNotFoundException: LoginServer
        at sun.rmi.registry.RegistryImpl_Skel.dispatch(Unknown Source)
        at sun.rmi.server.UnicastServerRef.oldDispatch(Unknown Source)
        at sun.rmi.server.UnicastServerRef.dispatch(Unknown Source)
        at sun.rmi.transport.Transport$1.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at sun.rmi.transport.Transport.serviceCall(Unknown Source)
        at sun.rmi.transport.tcp.TCPTransport.handleMessages(Unknown Source)
        at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(Unknown Sou
rce)
        at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(Unknown Sour
ce)
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source
)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.ClassNotFoundException: LoginServer
        at java.net.URLClassLoader$1.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClassInternal(Unknown Source)
        at java.lang.Class.forName0(Native Method)
        at java.lang.Class.forName(Unknown Source)
        at sun.rmi.server.LoaderHandler.loadProxyInterfaces(Unknown Source)
        at sun.rmi.server.LoaderHandler.loadProxyClass(Unknown Source)
        at sun.rmi.server.LoaderHandler.loadProxyClass(Unknown Source)
        at java.rmi.server.RMIClassLoader$2.loadProxyClass(Unknown Source)
        at java.rmi.server.RMIClassLoader.loadProxyClass(Unknown Source)
        at sun.rmi.server.MarshalInputStream.resolveProxyClass(Unknown Source)
        at java.io.ObjectInputStream.readProxyDesc(Unknown Source)
        at java.io.ObjectInputStream.readClassDesc(Unknown Source)
        at java.io.ObjectInputStream.readOrdinaryObject(Unknown Source)
        at java.io.ObjectInputStream.readObject0(Unknown Source)
        at java.io.ObjectInputStream.readObject(Unknown Source)
        ... 12 more

I was confused as heck when I first saw this. I could see the class file it said didn't exist, but I could see it in my code directory, plain as day. That's when I discovered that it didn't compile my remote interface into stub and skeleton files. In the past, you had to use the RMI compiler to manually generate these files, but it's supposedly automatic now. So why didn't it do it?! Is it having trouble identifying my interface as a remote interface?

That's got to be it as far as I can tell. Here's the code for the interface which was supposed to generate stub and skeleton files:

import java.rmi.RemoteException;

public interface LoginServer extends java.rmi.Remote
{
	public Player loginPlayer(java.net.Socket playerSocket)
		throws RemoteException;
}

[Jaikiran Pai]

"Just another programmer"

Please click the "My Private Messages" link (at the top of this page) for a message from JavaRanch.

[Martijn Verburg]

Hi Aaron and welcome to Javaranch!

What JDK are you using? Are you writing EJB's or POJOs with remoting?

[Aaron Ballard]

Martijn Verburg wrote:Hi Aaron and welcome to Javaranch!

What JDK are you using? Are you writing EJB's or POJOs with remoting?

I'm using what I'm pretty sure is the latest JDK (1.6u13) and I'm just writing POJO's, I'm not even using a real IDE.

A message to Pai: I can understand you wanting me to change my name, but why did you modify my topic name? Really, that's pretty dull.

[Martijn Verburg]

Are both the server and the client running on JRE 1.6 and were compiled by JDK 1.6 for a 1.6 environment (just double checking).

[Aaron Ballard]

Martijn Verburg wrote:Are both the server and the client running on JRE 1.6 and were compiled by JDK 1.6 for a 1.6 environment (just double checking).

Yep yep yep! I'm guessing this isn't one of those "simple solution" kinda things, huh?

[Martijn Verburg]

vaguely useful post here, not sure apart from that, maybe you should try the explicit creation using the rmi compiler?

[Aaron Ballard]

Martijn Verburg wrote:vaguely useful post here, not sure apart from that, maybe you should try the explicit creation using the rmi compiler?

I was originally going to try using the compiler manually as you said, but it seems that it was removed from the JDK after it was integrated into the main compiler, because it's not in my JDK bin directory.

Also, I'll check out that posts. Thanks for the help.

Edit: Never mind, the rmic compiler is there. I was really tired and accidentally looked in the JRE bin directory instead.

[Aaron Ballard]

Well, I successfully used the rmic utility to generate the stub and skeleton files, but now it's just doing the same thing but with the stub class.

Exception in thread "main" java.rmi.ServerException: RemoteException occurred in
 server thread; nested exception is:
        java.rmi.UnmarshalException: error unmarshalling arguments; nested exception is:
        java.lang.ClassNotFoundException: Server_Stub
        at sun.rmi.server.UnicastServerRef.oldDispatch(Unknown Source)
        at sun.rmi.server.UnicastServerRef.dispatch(Unknown Source)
        at sun.rmi.transport.Transport$1.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at sun.rmi.transport.Transport.serviceCall(Unknown Source)
        at sun.rmi.transport.tcp.TCPTransport.handleMessages(Unknown Source)
        at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(Unknown Source)
        at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)
        at sun.rmi.transport.StreamRemoteCall.exceptionReceivedFromServer(Unknown Source)
        at sun.rmi.transport.StreamRemoteCall.executeCall(Unknown Source)
        at sun.rmi.server.UnicastRef.invoke(Unknown Source)
        at sun.rmi.registry.RegistryImpl_Stub.bind(Unknown Source)
        at java.rmi.Naming.bind(Unknown Source)
        at Server.main(Server.java:49)
Caused by: java.rmi.UnmarshalException: error unmarshalling arguments; nested exception is:
        java.lang.ClassNotFoundException: Server_Stub
        at sun.rmi.registry.RegistryImpl_Skel.dispatch(Unknown Source)
        at sun.rmi.server.UnicastServerRef.oldDispatch(Unknown Source)
        at sun.rmi.server.UnicastServerRef.dispatch(Unknown Source)
        at sun.rmi.transport.Transport$1.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at sun.rmi.transport.Transport.serviceCall(Unknown Source)
        at sun.rmi.transport.tcp.TCPTransport.handleMessages(Unknown Source)
        at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(Unknown Source)
        at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.ClassNotFoundException: Server_Stub
        at java.net.URLClassLoader$1.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClassInternal(Unknown Source)
        at java.lang.Class.forName0(Native Method)
        at java.lang.Class.forName(Unknown Source)
        at sun.rmi.server.LoaderHandler.loadClass(Unknown Source)
        at sun.rmi.server.LoaderHandler.loadClass(Unknown Source)
        at java.rmi.server.RMIClassLoader$2.loadClass(Unknown Source)
        at java.rmi.server.RMIClassLoader.loadClass(Unknown Source)
        at sun.rmi.server.MarshalInputStream.resolveClass(Unknown Source)
        at java.io.ObjectInputStream.readNonProxyDesc(Unknown Source)
        at java.io.ObjectInputStream.readClassDesc(Unknown Source)
        at java.io.ObjectInputStream.readOrdinaryObject(Unknown Source)
        at java.io.ObjectInputStream.readObject0(Unknown Source)
        at java.io.ObjectInputStream.readObject(Unknown Source)
        ... 12 more

The server class references other classes and finds them just fine, but for some mysterious reason, the RMI api is not finding the classes. I swear this looks like it's not checking my classpath for the classes...

I've really had no end of misery with RMI... This is like, my third nightmare with it. Maybe I'll just use sockets for communication instead... They've got to be less resource-hungry too...

[Aaron Ballard]

Come on, there has got to be someone who knows what's going on...

[Nitesh Kant]

In order to utilize the dymanic proxies your server needs to extend UnicastRemoteObject.

  UnicastRemoteObject.exportObject(Remote)  

does not use the dynamic proxies as specified here

The exception suggests that the rmi registry where you are binding the server is not finding the stub classes.
You either need to enable dynmaic class downloading or put stubs and interfaces in the RMI Registry classpath OR start the registry programatically using LocateRegistry in the same java app that starts the server.

[Aaron Ballard]

Nitesh Kant wrote:In order to utilize the dymanic proxies your server needs to extend UnicastRemoteObject.

  UnicastRemoteObject.exportObject(Remote)  

does not use the dynamic proxies as specified here

The exception suggests that the rmi registry where you are binding the server is not finding the stub classes.
You either need to enable dynmaic class downloading or put stubs and interfaces in the RMI Registry classpath OR start the registry programatically using LocateRegistry in the same java app that starts the server.

Awesome! Someone who seems to know what they're talking about! I'll look into everything you just said and get back to you!