Java: Making a Remote Service

Steps

Server

• Make a remote interface
• Extend java.rmi.Remote
• Declare that all methods throw a RemoteException
• arguments and return value should be Serializable or primitives

ITestRemoteService.java

import java.rmi.*;

public interface ITestRemoteService extends Remote {

   public String helloWorld() throws RemoteException;

}

• Make a remote implementation
• Implement the remote interface
• Extend UnicastRemoteObject
• write no argument constructor that declares a RemoteException
• Register the service with the RMI registry

TestRemoteService.java

import java.rmi.*;

import java.rmi.server.*; // import for UnicastRemoteObject usage

public class TestRemoteService extends UnicastRemoteObject implements ITestRemoteService {

    

   public static void main(String[] args) {

       try{

           TestRemoteService myTestService = new TestRemoteService();

           Naming.rebind("TestRemoteService", myTestService); //bind to rmiregistry

       } catch(Exception ex) {

           ex.printStackTrace();

       }

   }

    

    

   public TestRemoteService() throws RemoteException {} //UnicastRemoteObject declares an exception

    

   public String helloWorld() {

       return "Hello, George!";

   }     

}

• Generate the stubs and skeletons (this is deprecated for new java versions) using rmic
• Split out the two new classes for the helper objects
• NOTE: In Java 5, RMI and Dynamic Proxy got toghether and now stubs are generated dynamically using Dynamic Proxy. The remote objcet's stub is a java.lang.reflect.Proxy instance (with an invocation handler).

>javac -d class ITestRemoteService.java

>javac -d class TestRemoteService.java

>cd class

>rmic TestRemoteService

• Start the RMI registry (rmiregistry)

>rmiregistry

• Start the remote service

>java TestRemoteService

Client

• Have a client class (in a client folder)
• Copy interface and stubs to the client folder
• Client does a lookup on the RMI registry
• RMI registry returns the stub object
• stub class should be on the client (also the interface class)
• Client invokes a method on the stub

TestRemoteClient.java

import java.rmi.*;

public class TestRemoteClient {

   public static void main(String[] args) {

       try {

           ITestRemoteService service = (ITestRemoteService) Naming.lookup("rmi://127.0.0.1/TestRemoteService");

           String str = service.helloWorld();

           System.out.println(str);

            

       } catch(Exception ex) {

           ex.printStackTrace();

       }

   }

}

>javac -d class TestRemoteClient.java

>cd class

>java TestRemoteClient

Hello, George!