Simple works

Question

hi guys!! ive tried to run a simple rmi test and i got a class not found exception.... so i figured i should try the example and see the what i was doing wrong and guess what? got the same error (except the implementing class name):
Caused by: java.rmi.UnmarshalException: error unmarshalling arguments; nested exception is:
     java.lang.ClassNotFoundException: example.hello.Server_Stub
     at sun.rmi.registry.RegistryImpl_Skel.dispatch(Unknown Source)
     at sun.rmi.server.UnicastServerRef.oldDispatch(UnicastServerRef.java:375)
     at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:240)
     at sun.rmi.transport.Transport$1.run(Transport.java:153)
     at java.security.AccessController.doPrivileged(Native Method)
     at sun.rmi.transport.Transport.serviceCall(Transport.java:149)
     at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:460)
     at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:701)
     at java.lang.Thread.run(Thread.java:595)
Caused by: java.lang.ClassNotFoundException: example.hello.Server_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:306)
     at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
     at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:319)
     at java.lang.Class.forName0(Native Method)
     at java.lang.Class.forName(Class.java:242)
     at sun.rmi.server.LoaderHandler.loadClass(LoaderHandler.java:430)
     at sun.rmi.server.LoaderHandler.loadClass(LoaderHandler.java:165)
     at java.rmi.server.RMIClassLoader$2.loadClass
ive tried with and without stub pregeneration (with rmic)... also, im sure that rmiregistry is running, but it should make any difference... and yes ive tried to override the classpath, but it doesnt make any difference... any advice?

Answer 1

Hi takeshi10,
When I was trying to run my first sample RMI code I experienced absolutely the same problems. Later on, I understood that the problem was caused because I do not set correctly any of the following properties:
1) java.rmi.server.codebase
2) java.security.policy
3) rmi.server.hostname
Now let me show you a simple client-server RMI example. In this example we will use one interface ServerCounter and two classes ServerCounterImpl and Client. ServerCounter is the interface of the remote object and ServerCounterImpl is the class that implements the remote interface. In our example we will register (bind) the ServerCounter object to the RMI registry and count the number of calls made by a Client instance. Whenever a client calls the "printVisiotorCounter" method the server will print the the name of the user calling the method and the current number of the call. Bellow is the source code of all interfaces and the. From now I will assume that the source files reside in �C:/HelloWorldRMI/� and will refer to this location as $rmiexample.
File: ServerCounter.java
import java.rmi.Remote;
import java.rmi.RemoteException;
public interface ServerCounter extends Remote {
     // Prints the number of the current visitor/caller
     // Note that the message will be printed on the console
     // where the server application runs!
     public void printVisiotorCounter(String user) throws RemoteException;
     // Unbinds the remotely registered object and the application
     // terminates.
     public void exitServer() throws RemoteException;
} // End of interface  ServerCounter
File: ServerCounterImpl.java
import java.rmi.Naming;
import java.rmi.RMISecurityManager;
import java.rmi.RemoteException;
import java.rmi.server.UnicastRemoteObject;
public class ServerCounterImpl extends UnicastRemoteObject implements ServerCounter {
     public ServerCounterImpl() throws RemoteException
          super();
          _visitorCounter = 0;
          _rmiRemoteObjUrl = "//localhost/ServerCounter";
     } // End of default constructor
     public void printVisiotorCounter(String user) throws RemoteException
          ++_visitorCounter;
          System.out.println("Hello " + user + ", you are the " + _visitorCounter + " visitor.");
     } // End of void printVisiotorCounter(String)
     public void exitServer() throws RemoteException
          try
               Naming.unbind(_rmiRemoteObjUrl);
               System.out.println("Server unregistered successfully");               
          catch (Exception ex)
               ex.printStackTrace();
     } // End of void exitServer()
     public static void main(String[] args) {
          if (System.getSecurityManager() == null)
               System.setSecurityManager(new RMISecurityManager());
          String rmiObjId = "ServerCounter";
          String _rmiRemoteObjUrl = "//localhost/" + rmiObjId;
          try
               ServerCounter sc = new ServerCounterImpl();
               // Register the Server to the RMI registry
               Naming.bind(_rmiRemoteObjUrl, sc);
               System.out.println();
          catch (Exception ex)
               ex.printStackTrace();
          System.out.println("Server's main thread is about to exit!");
     } // End of void main(String[])
     // Stores the number of visitors
     private int _visitorCounter;
     // The URL through which this object can be accessed
     // from the RMI registry.     
     private String _rmiRemoteObjUrl;
     private static final long serialVersionUID = 0;
} // End of class ServerCounterImpl
File: Client.java
import java.rmi.Naming;
public class Client {
     public static void main(String[] args) {
          String user = args[0];
          try
               String serverUrl = "//localhost/ServerCounter";
               ServerCounter sc = (ServerCounter)Naming.lookup(serverUrl);
               if (user.compareToIgnoreCase("exit") != 0)
                    sc.printVisiotorCounter(user);
               else sc.exitServer();
          catch (Exception ex)
               ex.printStackTrace();
     } // End of void main(String[])
} // End of class Client
compile.bat � use this file to compile your classes
File: compile.bat
javac Client.java
javac ServerCounter.java
javac ServerCounterImpl.java
rmic ServerCounterImpl
runserver.bat � use this file to run the server. Before calling this script do not forget to start the rmiregistry! It is appreciated to call this script from the console by typing �rmiregistry.bat� instead of double clicking on it.
File: runserver.bat
java \
-Djava.rmi.server.codebase="file:/C:/HelloWorldRMI/" \
-Djava.security.policy="security.policy" ServerCounterImpl \
-Djava.rmi.server.hostname="localhost" \
ServerCounterImplRunning Client
Now to run the client you need to pass a command line argument that specifies your name, or your desire to unbind and terminate the remote object (the ServerCounter).
java \
-Djava.rmi.server.codebase="file:/C:/HelloWorldRMI/" \
-Djava.security.policy="security.policy" ServerCounterImpl \
-Djava.rmi.server.hostname="localhost" \
Client <Your_Name>To unbind the remote object invoke:
java \
-Djava.rmi.server.codebase="file:/C:/HelloWorldRMI/" \
-Djava.security.policy="security.policy" ServerCounterImpl \
-Djava.rmi.server.hostname="localhost" \
Client exitNOTE: Ensure that all the abouve mentioned files ServerCounter.java ServerCounterImpl.java Client.java compile.bat runserver.bat reside within $rmiexample (C:/HelloWorldRMI/)
Hope that this example was helpful to you. Be careful with the command line parameters because they may cause your example to fail. By the way, it works on me.
Regards,
Ferad Zyulkyarov