Java RMI (Remote Method Invocation)

Java RMI (Remote Method Invocation) is a Java API that enables remote communication between two Java programs. It allows a client program to execute methods on a server program, as if the server program is running on the client's machine. It is a powerful tool for developing distributed systems and allows developers to build complex distributed applications.

Syntax

To use Java RMI, you need to define an interface that specifies the methods that the client can call on the server. You also need to implement the server class that provides the implementation for these methods. Finally, you need to register the server with the RMI registry, which is a service that allows clients to discover the server's location.

Example

Here's an example of a Java RMI program that adds two integers:

// The remote interface
import java.rmi.*;

public interface Adder extends Remote {
    public int add(int x, int y) throws RemoteException;
}

// The server class
import java.rmi.*;
import java.rmi.server.*;

public class AdderImpl extends UnicastRemoteObject implements Adder {
    public AdderImpl() throws RemoteException {}

    public int add(int x, int y) throws RemoteException {
        return x + y;
    }
}

// The main class
import java.rmi.*;

public class Client {
    public static void main(String[] args) {
        try {
            String url = "rmi://localhost/AdderService";
            Adder adder = (Adder)Naming.lookup(url);
            int sum = adder.add(2, 3);
            System.out.println(sum);
        } catch (Exception e) {
            System.out.println(e);
        }
    }
}

In this example, we define the Adder interface, which has a single method that adds two integers. We implement the AdderImpl class, which provides the implementation for this method. We then register the AdderImpl class with the RMI registry using the URL rmi://localhost/AdderService. Finally, we create a Client class that looks up this URL in the RMI registry and calls the add method on the remote object.

Output

When you run this program, it should output the sum of 2 and 3:

5

Explanation

Java RMI works by allowing a client program to execute methods on a server program running on a different machine. The client program uses a proxy object, called a stub, to call methods on the remote object. The stub marshals the method parameters into a network format and sends them over the network to the server. The server unmarshals the parameters and executes the requested method. The server then marshals the return value, sends it back to the client, and the client unmarshals the return value.

Use

Java RMI is used for building distributed systems where different parts of the system need to communicate with each other. It is used in many different applications, including online transaction processing systems, distributed databases, and e-commerce applications.

Important Points

• Java RMI is a Java API that enables remote communication between two Java programs.
• Java RMI works by allowing a client program to execute methods on a server program running on a different machine.
• Java RMI is used for building distributed systems where different parts of the system need to communicate with each other.

Summary

Java RMI is a powerful tool for developing distributed systems and allows developers to build complex distributed applications. It is used in many different applications, including online transaction processing systems, distributed databases, and e-commerce applications. By enabling remote communication between two Java programs, Java RMI makes it possible to build applications that scale to meet the needs of large, distributed systems.