CORBA in Java: A Step-by-Step Guide

Overview

This guide walks you through creating a simple CORBA application in Java, where a client communicates with a server to receive a message. We'll use Java 1.8 to implement CORBA (Common Object Request Broker Architecture) and define an IDL (Interface Definition Language) interface to facilitate communication between the client and server.

Objective:

The goal is to design, develop, and test the "hello" application (a program that displays "hello" on the server).

Files to be created:

• hello.idl: Interface of the Hello application
• Server.java: Implementation of the Hello application server
• Client.java: Implementation of the Hello application client
• Hello_impl.java: Implementation of the Hello object in the Hello application

Application Steps:

1. Compile the IDL file:

   idlj -fall hello.idl

   • Ensure a directory named hello is created.
   • A set of classes will be generated by the IDL compiler.
   • Open each file generated.

2. Develop the client and server: Copy the client, server, and implementation object into the hello directory (or package if using an IDE).

3. Compile the client, server, and files generated by the IDL compiler:

   javac hello/*.java

4. Start the server:

   java hello.Server

   • A file corresponding to the IOR will be created in string format; open this file.

5. Run the client:

   java hello.Client

   • Modify the program so that it displays "hello" on the client.
   • Run the client from another machine (explain the procedure).

Prerequisites

• Java 1.8 must be installed on your machine.
• CORBA IDL Compiler (idlj) must be available.

Steps

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1. Install Java 1.8

Ensure you have Java 1.8 installed on your system. You can download it from the official Oracle archive:

• Download Java SE 8

Installation Instructions:

1. Install Java by following the instructions on the website.
2. After installation, add the bin folder to your system's PATH. This allows Java and CORBA tools like idlj to be executed from the command line.

Example PATH:

C:\Program Files\Java\jdk1.8.0_202\bin

2. Verify Installation

Check if idlj (the IDL compiler) is available by running the following command in your terminal or command prompt:

idlj -version

If the command runs successfully and shows the version, you're ready to proceed.

3. Write an IDL File

Create a new file named hello.idl. This file defines the CORBA interface, which will be used for communication between the client and server.

interface Hello {
    void hello();
};

4. Compile the IDL File

Use the CORBA IDL compiler to generate the necessary classes for both client and server communication.

Run the following command:

idlj -fall hello.idl

After Compilation:

• A new directory named hello will be created.
• Several Java classes will be generated. These include stubs and skeletons necessary for CORBA communication.

Make sure to open and review the generated files to understand the communication structure.

5. Implement the Server and Client

Now that the IDL has been compiled, implement the server and client in Java. Use the generated classes to handle CORBA object communication.

HelloImpl.java

public class HelloImpl extends HelloPOA {
    @Override
    public void hello() {
        System.out.println("Hello");
    }
}

Server.java

import org.omg.CORBA.UserException;
import org.omg.PortableServer.POA;
import org.omg.PortableServer.POAHelper;
import org.omg.PortableServer.POAManager;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.PrintWriter;


public class Server {
    public static void main(String args[]) {
        java.util.Properties props = System.getProperties();
        int status = 0;
        org.omg.CORBA.ORB orb = null;

        try {
            orb = org.omg.CORBA.ORB.init(args, props);
            status = run(orb);
        } catch (Exception ex) {
            ex.printStackTrace();
            status = 1;
        }

        if (orb != null) {
            try {
                orb.destroy();
            } catch (Exception ex) {
                ex.printStackTrace();
                status = 1;
            }
        }
        System.exit(status);
    }

    static int run(org.omg.CORBA.ORB orb) throws UserException, IOException {
        POA rootPOA;
        POAManager manager;

        rootPOA = POAHelper.narrow(orb.resolve_initial_references("RootPOA"));
        manager = rootPOA.the_POAManager();

        HelloImpl helloImpl = new HelloImpl();
        Hello hello = helloImpl._this(orb);

        String ref = orb.object_to_string(hello);
        String refFile = "Hello.ref";
        FileOutputStream file = new FileOutputStream(refFile);
        PrintWriter out = new PrintWriter(file);
        out.println(ref);
        file.close();

        try {
            if (manager != null) {
                manager.activate();
            }
            orb.run();
        } catch (Exception e) {
            e.printStackTrace();
            return 1;
        }

        return 0;
    }
}

Client.java

import org.omg.CORBA.ORB;

import java.io.*;

public class Client {
    public static void main(String[] args) {
        java.util.Properties props = System.getProperties();
        int status;
        ORB orb = null;

        try {
            orb = org.omg.CORBA.ORB.init(args, props);
            status = run(orb);

        } catch (Exception ex) {
            ex.printStackTrace();
            status = 1;
        }

        if (orb != null) {
            try {
                orb.destroy();
            } catch (Exception ex) {
                ex.printStackTrace();
                status = 1;
            }
        }

        System.exit(status);
    }

    static int run(org.omg.CORBA.ORB orb) throws IOException {
        org.omg.CORBA.Object obj;

        String refFile = "Hello.ref";
        FileInputStream file = new FileInputStream(refFile);
        BufferedReader in = new BufferedReader(new InputStreamReader(file));
        String ref = in .readLine();
        file.close();

        obj = orb.string_to_object(ref);

        Hello hello = HelloHelper.narrow(obj);
        hello.hello();
        return 0;
    }
}

6. Run the Server and Client

After implementing both the client and server:

1. Run the Server:

   • Open a terminal and execute the following command:

   java Server

2. Run the Client:

   • Open another terminal and execute the following command:

   java Client

If everything is set up correctly, the client will print Hello from the server! to the console.

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Summary

This guide showed how to implement a simple CORBA-based client-server system in Java. By following these steps, you've defined a CORBA interface, compiled the necessary Java classes, implemented the server and client, and executed the communication between them.