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Tags/Keywords : Java RMI, RMI Example, RMI Code, Java RMI Example, Java Platform
Author : Amit
Date (Year/Month/Date): 2009-07-10
Java RMI Example with code explained

Please be informed that NONE of the design/code from this
page is claiming to be some sort of best practices and we DO NOT expect
any of our visitor/reader of this page to assume this as some sort of
best practice for any context and should not be using this 
as it is without appropriate evaluation to their, so to say, 
specific programming context.

This page intends only to provide bit and piece of known ways  for
doing some sort of example and may not be fit for any other purpose.


Tags: RMI example, RMI Code, Java RMI example

If you have started learning Java technology recently, then this example
could be very basic and preliminary help in understanding RMI using an
example code. If you already know RMI, then this example could serve you
with a refresh of this concept with very basic example code.



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My Software environment for this example:
1. Eclipse 3.2
2. JDK 1.5

Idea here is to show way to call a remote method from a different JVM 
from a command line based application.
So we have two command line based program, one program locates an already
running RMIRegistry with a port number 1099, and binds the remote object
(an object from a class that extends java.rmi.server.UnicastRemoteObject
and implements an interface that extends java.rmi.Remote).


And the other program locates an already running RMIRegistry and lookup
the already bound remote object.

So we have to define an interface that extends java.rmi.Remote
and a class that extends UnicastRemoteObject and implements this interface.

ExampleRemote.java

//This code is provided "AS IS"
package example;

import java.rmi.Remote;
import java.rmi.RemoteException;

public interface ExampleRemote extends Remote {
  public String test() throws RemoteException;
}


ExampleRemoteObject.java

//This code is provided "AS IS"
package example;

import java.rmi.RemoteException;
import java.rmi.server.UnicastRemoteObject;

public class ExampleRemoteObject extends UnicastRemoteObject
          implements ExampleRemote {
    public ExampleRemoteObject() throws RemoteException {
      super();
    }
    public String test() throws RemoteException {
      System.out.println("inside test method in ExampleRemoteObject");
      return "from test method";
    }
}

Those two commandline Java programs as follows:

TestClient.java

//This code is provided "AS IS"
package example;

import java.rmi.AlreadyBoundException;
import java.rmi.RemoteException;
import java.rmi.registry.Registry;
import java.rmi.registry.LocateRegistry;

public class TestClient {

  public TestClient() {
    try {
      ExampleRemoteObject remoteObject = new ExampleRemoteObject();
      Registry registry = LocateRegistry.getRegistry("localhost", 1099);
      registry.bind("exampleremote", remoteObject );
    } catch (RemoteException e) {
      e.printStackTrace();
    } catch (AlreadyBoundException e) {
      e.printStackTrace();
    }
  }
  
  public static void main(String[] args) {
    new TestClient();
  }
}

The other program that should be called from another command prompt, this
way we can simulate environment with two different JVM and ClassLoader.

TestRMIClient.java

//This code is provided "AS IS"
package example;

import java.rmi.NotBoundException;
import java.rmi.RemoteException;
import java.rmi.registry.LocateRegistry;
import java.rmi.registry.Registry;

public class TestRMIClient {

  public TestRMIClient() {
    try {
      Registry registry = LocateRegistry.getRegistry("localhost",1099);
      ExampleRemote exampleR = (ExampleRemote) registry.lookup("exampleremote");
      System.out.println(exampleR.test());
    } catch (RemoteException e) {
      e.printStackTrace();
    } catch (NotBoundException e) {
      e.printStackTrace();
    }
		
  }

  public static void main(String[] args) {
    new TestRMIClient();
  }
}

One question may you be thinking is what is this RMI registry that is located
in the client programs with a HOST address as localhost and port as 1099?

This is nothing but the rmiregistry.exe program found under %JAVA_HOME%\bin 
folder.

One thing to remember is that, before running this rmiregistry.exe program, 
classpath environment should be having the folder to the 
example.ExampleRemote class, or else you might get exception such as
Caused by: java.lang.ClassNotFoundException: example.ExampleRemote

If everything setup properly, then one may run TestClient to have this program
stays running till the other client program, that is TestRMIClient is run,
in another command prompt, to receive system out as follows:

java TestClient
inside test method in ExampleRemoteObject

java TestRMIClient
from test method

This shows that TestRMIClient is able to invoke test method from the
other TestClient running program and able to receive "from test method"
returned value from the test method.



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In my another example on RMI, I shall explore way to use Spring 
Remoting feature with RMI. Please keeep reading my examples
and comment on this to improve my examples, and please let me know
if this really helped you with your understanding of the topic
on hand.

Author of this article/writeup has expressed his/her willingness
to help or guide users with any technical difficulties he/she faces
while working with the example code environment setting up, running
and resolving any such exception raised during compile or at runtime.
You may ask for any technical doubt or seek technical help related to
this article by using following form to reach for technical help
from the Author for FREE.

This article's Author shall be reading your request and responding
within reasonable time (no resolution timeframe defined as such).

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