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RMI (Remote Method Invocation) Project

A comprehensive Java Remote Method Invocation (RMI) application that demonstrates client-server communication and remote object invocation.

Project Overview

This project implements a classic RMI example where a server hosts multiple product objects and clients can remotely access these products to retrieve their information (name, description, and price) over the network.

Architecture

System Components

Client Side
├── Client.java               # Main client application
└── Product.java              # Remote interface for product operations

Server Side
├── Server.java               # Main server application  
├── Product.java              # Remote interface (same as client)
├── ProductImpl.java          # Implementation of Product interface
└── ProductImpl.class         # Compiled implementation

Entry Point
└── Main.java                 # Simple hello world example (not part of RMI system)

Key Components

  1. Remote Interface (Product.java): Defines the contract for remote operations

    • getName() - Returns product name
    • getDescription() - Returns product description
    • getPrice() - Returns product price

  2. Implementation (ProductImpl.java): Implements the remote interface

    • Contains product data (name, description, price)
    • Provides actual implementations of remote methods

  3. Server (Server.java): RMI Server Application

    • Creates multiple product instances
    • Exports objects for remote access
    • Registers objects in RMI registry
    • Hosts 4 different products (Product1-4)

  4. Client (Client.java): RMI Client Application

    • Connects to RMI registry
    • Looks up remote objects by name
    • Invokes remote methods to get product information

Setup Instructions

Prerequisites

  • Java Development Kit (JDK) 8 or higher
  • Java Runtime Environment (JRE) 8 or higher
  • Integrated Development Environment (IDE) like IntelliJ IDEA, Eclipse, or VS Code

Configuration

The application is configured for localhost operation:

  • Server IP: 127.0.0.1 (localhost)
  • RMI Registry Port: 1099
  • Hostname: 127.0.0.1

How to Run the RMI System

Step 1: Compile the Code

# Compile all Java files
javac -d . src/**/*.java

Step 2: Start the RMI Registry

# Start RMI registry (in background)
rmiregistry &

Step 3: Start the Server

# Run the server application
java -cp . server.Server

Step 4: Run the Client

# Run the client application
java -cp . client.Client

Alternative: Run in IDE

  1. Open the project in your IDE
  2. Run Server.java first (right-click → Run)
  3. Run Client.java second (right-click → Run)

Expected Output

Server Output

  • Server starts successfully
  • Creates 4 product instances
  • Exports and registers them in RMI registry
  • No console output when running successfully

Client Output

Product Name: Product 1
Product Description: Description of Product 1
Product Price: 10.99

Technical Details

RMI Flow

  1. Server Initialization:

    • Creates ProductImpl instances with sample data
    • Exports objects using UnicastRemoteObject.exportObject()
    • Registers objects in RMI registry with names "Product1" to "Product4"
    • Sets hostname property for network access

  2. Client Operation:

    • Locates RMI registry on localhost:1099
    • Looks up remote objects by registry names
    • Casts retrieved objects to Product interface
    • Invokes remote methods to get product information

Network Configuration

  • Registry: Uses default RMI registry port 1099
  • Hostname: Configured as 127.0.0.1 for local testing
  • Protocol: Uses Java RMI protocol (JRMP)

File Structure

RMI/
├── README.md                    # This documentation
├── RMI.iml                      # IntelliJ IDEA module configuration
└── src/
    ├── Main.java                # Hello world example (not RMI-related)
    ├── client/
    │   ├── Client.java          # RMI Client application
    │   └── Product.java         # Remote interface
    └── server/
        ├── Product.java         # Remote interface (same as client)
        ├── ProductImpl.java     # Implementation of Product interface
        └── Server.java          # RMI Server application

Troubleshooting

Common Issues

  1. RMI Registry Not Running:

    java.rmi.ConnectException: Connection refused to host: 127.0.0.1; nested exception is: 
java.net.ConnectException: Connection refused

    Solution: Start rmiregistry before running the server

  2. ClassNotFoundException:

    java.lang.ClassNotFoundException: client.Product

    Solution: Ensure proper classpath with -cp . or use IDE's run configuration

  3. AlreadyBoundException:

    java.rmi.server.AlreadyBoundException: Product1

    Solution: Restart the server to clear registry or use different binding names

  4. Security Manager Issues: If using security policies, ensure proper permissions are granted

Debug Tips

  1. Check Registry: Verify that objects are properly registered
  2. Network: Ensure no firewall blocks port 1099
  3. Classpath: Verify all compiled classes are accessible
  4. Server Order: Always start server before client

Dependencies

  • Java RMI API (built-in with JDK)
  • No external dependencies required

Development Notes

  • The Main.java file contains a simple hello world example and is not part of the RMI system
  • The project uses separate packages for client and server code organization
  • All remote methods throw RemoteException as required by RMI specification
  • The implementation uses UnicastRemoteObject for remote object export

Educational Purpose

This project serves as a practical demonstration of:

  • Remote Method Invocation concepts
  • Client-server architecture
  • Remote object lifecycle management
  • Network programming in Java
  • Interface-based remote design patterns

Created for Advanced Programming Course - Semester 5
University of Ruhuna