Editing Java remote method invocation (section)

==Example==
The following classes implement a simple client-server program using RMI that displays a message.

; <code>RmiServerIntf</code> interface : defines the interface that is used by the client and implemented by the server. This extends the {{Javadoc:SE|module=java.rmi|package=java.rmi|java/rmi|Remote}} interface, which serves to identify an implementing class as one with remotely-invokable methods.

<syntaxhighlight lang=java>
import java.rmi.Remote;
import java.rmi.RemoteException;

public interface RmiServerIntf extends Remote {
    String getMessage() throws RemoteException;
}
</syntaxhighlight>

; <code>RmiServer</code> class : listens to RMI requests and implements the interface which is used by the client to invoke remote methods.

<syntaxhighlight lang=java>
import java.rmi.Naming;
import java.rmi.RemoteException;
import java.rmi.server.UnicastRemoteObject;
import java.rmi.registry.*;

public class RmiServer extends UnicastRemoteObject implements RmiServerIntf {
    public static final String MESSAGE = "Hello World";

    public RmiServer() throws RemoteException {
        super(0); // required to avoid the 'rmic' step, see below
    }

    public String getMessage() {
        return MESSAGE;
    }

    public static void main(String[] args) throws Exception {
        System.out.println("RMI server started");

        try { //special exception handler for registry creation
            LocateRegistry.createRegistry(1099);
            System.out.println("java RMI registry created.");
        } catch (RemoteException e) {
            //do nothing, error means registry already exists
            System.out.println("java RMI registry already exists.");
        }
           
        //Instantiate RmiServer
        RmiServer server = new RmiServer();

        // Bind this object instance to the name "RmiServer"
        Naming.rebind("//localhost/RmiServer", server);
        System.out.println("PeerServer bound in registry");
    }
}
</syntaxhighlight>

; <code>RmiClient</code> class : this is the client which gets the reference (a proxy) to the remote object living on the server and invokes its method to get a message. If the server object implemented java.io.Serializable instead of java.rmi.Remote, it would be serialized and passed to the client as a value.<ref>{{cite web |last1=Wilson |first1=M. Jeff |date=2000-11-10 |df=mdy |url=https://www.infoworld.com/article/2076234/get-smart-with-proxies-and-rmi.html |title=Get smart with proxies and RMI |work=[[JavaWorld]] |access-date=2020-07-18}}</ref>

<syntaxhighlight lang=java>
import java.rmi.Naming;

public class RmiClient {
    public static void main(String[] args) throws Exception {
        RmiServerIntf server = (RmiServerIntf)Naming.lookup("//localhost/RmiServer");
        System.out.println(server.getMessage());
    }
}
</syntaxhighlight>

Before running this example, we need to make a 'stub' file for the interface we used. For this task we have the RMI compiler - 'rmic'
*Note: we make a stub file from the '*.class' file with the implementation of the remote interface, not from the '*.java' file.

 rmic RmiServer

Note that since version 5.0 of J2SE, support for dynamically generated stub files has been added, and rmic is only provided for backwards compatibility with earlier runtimes,<ref>{{cite web|title=Java RMI Release Notes|url=http://docs.oracle.com/javase/1.5.0/docs/guide/rmi/relnotes.html|publisher=Oracle|access-date=9 May 2012}}</ref> or for programs that don't provide an explicit port number (or zero) when exporting remote objects, which is required for generated stubs to be possible, as described in the Javadoc for {{Javadoc:SE|module=java.rmi|java/rmi/server|UnicastRemoteObject}}. See the comment in the constructor above.