Using RMI from within Eclipse

[Sean Keane]

Hi,

As part of getting up to speed with RMI for the OCJD I am playing around with some examples. I am having difficulty getting an RMI example running in Eclipse, can anyone help?

The example that I am trying to run is from this page here http://download.oracle.com/javase/6/docs/technotes/guides/rmi/hello/hello-world.html

I compiled all the classes from this example into "F:\classes", so they exist in "F:\classes\example\hello". I have the following structure:

F:.
└───classes
    └───example
        └───hello
                Client.class
                Client.java
                Hello.class
                Hello.java
                Server.class
                Server.java

The example runs from the command line when I do the following:

1. Run rmiregistry from a command window, where the directory is somewhere other than where the code is located, and CLASSPATH is blank.

2. Run the server using the command, which is run from the directory "F:": java -classpath classes -Djava.rmi.server.codebase=file:F:/classes/ example.hello.Server

3. Run the client using the command below run from the directory "F:" : java -cp classes example.hello.Client

Now, when I copy all the files to Eclipse it no longer runs for me. The directory structure in Eclipse is:

F:
+---RMI
¦   ¦   .classpath
¦   ¦   .project
¦   ¦
¦   +---.settings
¦   ¦       org.eclipse.jdt.core.prefs
¦   ¦
¦   +---classes
¦   ¦   +---example
¦   ¦       +---hello
¦   ¦               Client.class
¦   ¦               Hello.class
¦   ¦               Server.class
¦   ¦
¦   +---src
¦       +---example
¦           +---hello
¦                   Client.java
¦                   Hello.java
¦                   Server.java

So, I first start the rmiregistry from a command window, where the directory is somewhere other than where the code is located, and CLASSPATH is blank.

Then I attempt to run the Server class in Eclipse. I set the VM arguments to include the following:

-Djava.rmi.server.codebase=file:F:\RMI\classes

But then I get this error below. Any ideas why the class example.hello.Hello cannot be found?

Server exception: java.rmi.ServerException: RemoteException occurred in server thread; nested exception is: 
	java.rmi.UnmarshalException: error unmarshalling arguments; nested exception is: 
	java.lang.ClassNotFoundException: example.hello.Hello
java.rmi.ServerException: RemoteException occurred in server thread; nested exception is: 
	java.rmi.UnmarshalException: error unmarshalling arguments; nested exception is: 
	java.lang.ClassNotFoundException: example.hello.Hello
	at sun.rmi.server.UnicastServerRef.oldDispatch(UnicastServerRef.java:396)
	at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:250)
	at sun.rmi.transport.Transport$1.run(Transport.java:159)
	at java.security.AccessController.doPrivileged(Native Method)
	at sun.rmi.transport.Transport.serviceCall(Transport.java:155)
	at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:535)
	at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:790)
	at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:649)
	at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
	at java.lang.Thread.run(Thread.java:662)
	at sun.rmi.transport.StreamRemoteCall.exceptionReceivedFromServer(StreamRemoteCall.java:255)
	at sun.rmi.transport.StreamRemoteCall.executeCall(StreamRemoteCall.java:233)
	at sun.rmi.server.UnicastRef.invoke(UnicastRef.java:359)
	at sun.rmi.registry.RegistryImpl_Stub.bind(Unknown Source)
	at example.hello.Server.main(Server.java:24)
Caused by: java.rmi.UnmarshalException: error unmarshalling arguments; nested exception is: 
	java.lang.ClassNotFoundException: example.hello.Hello
	at sun.rmi.registry.RegistryImpl_Skel.dispatch(Unknown Source)
	at sun.rmi.server.UnicastServerRef.oldDispatch(UnicastServerRef.java:386)
	at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:250)
	at sun.rmi.transport.Transport$1.run(Transport.java:159)
	at java.security.AccessController.doPrivileged(Native Method)
	at sun.rmi.transport.Transport.serviceCall(Transport.java:155)
	at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:535)
	at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:790)
	at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:649)
	at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
	at java.lang.Thread.run(Thread.java:662)
Caused by: java.lang.ClassNotFoundException: example.hello.Hello
	at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
	at java.lang.Class.forName0(Native Method)
	at java.lang.Class.forName(Class.java:247)
	at sun.rmi.server.LoaderHandler.loadProxyInterfaces(LoaderHandler.java:711)
	at sun.rmi.server.LoaderHandler.loadProxyClass(LoaderHandler.java:655)
	at sun.rmi.server.LoaderHandler.loadProxyClass(LoaderHandler.java:592)
	at java.rmi.server.RMIClassLoader$2.loadProxyClass(RMIClassLoader.java:628)
	at java.rmi.server.RMIClassLoader.loadProxyClass(RMIClassLoader.java:294)
	at sun.rmi.server.MarshalInputStream.resolveProxyClass(MarshalInputStream.java:238)
	at java.io.ObjectInputStream.readProxyDesc(ObjectInputStream.java:1530)
	at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1492)
	at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1731)
	at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1328)
	at java.io.ObjectInputStream.readObject(ObjectInputStream.java:350)
	... 12 more

Below is the code that I am trying to run, I've only included the Server class, the Client class and Hello interface are on the link I mentioned above.

package example.hello;

import java.rmi.registry.Registry;
import java.rmi.registry.LocateRegistry;
import java.rmi.RemoteException;
import java.rmi.server.UnicastRemoteObject;

public class Server implements Hello {

    public Server() {}

    public String sayHello() {
        return "Hello, world!";
    }

    public static void main(String args[]) {

        try {
            Server obj = new Server();
            Hello stub = (Hello) UnicastRemoteObject.exportObject(obj, 0);

            // Bind the remote object's stub in the registry
            Registry registry = LocateRegistry.getRegistry();
            registry.bind("Hello", stub);

            System.err.println("Server ready");
        } catch (Exception e) {
            System.err.println("Server exception: " + e.toString());
            e.printStackTrace();
        }
    }
}

[Sean Keane]

Just to note. If I run the rmiregistry from the location my .class files are generated into i.e. "F:\RMI\classes", then the Server class will run from within Eclipse.

But from what I understand, you shouldn't run the rmiregistry from the location where the class files are available, and you shouldn't have the location of the class files on the CLASSPATH environment variable that is available to the rmiregistry. The reason being that the rmiregistry will simply pick up the class files from the current directory or the location on the CLASSPATH rather than the location specified in the JVM argument -Djava.rmi.server.codebase.

I confirmed that the value of -Djava.rmi.server.codebase is being ignored when the rmiregistry is run from the directory containing the class files by setting the value of -Djava.rmi.server.codebase to an invalid value in Eclipse, the Server class still runs, which shows that the value of -Djava.rmi.server.codebase is being ignored.

[Sean Keane]

Ahhh schoolboy error! I was using the following VM argument in Eclipse when attempting to run the Server class:

-Djava.rmi.server.codebase=file:F:\RMI\classes

When I should have been using this:

-Djava.rmi.server.codebase=file:F:\RMI\classes\

Note the extra path separator at the end!

The Server now runs for me successfully in Eclipse based on the information above, happy days .

[Roberto Perillo]

Howdy, Sean!

Champ, just remember that your application must not require any command line arguments other than the flag that indicates the application mode.

[Sean Keane]

Cheers Roberto. I will keep that in mind. I've never used RMI before. So at the moment I'm just playing around with it a bit to get a feel for it.