Java remote method invocation - Java RMI Tutorial

1- Introduction

RMI is a way for you to call remote method. for example, call a method running on a computer B and receive the resulting response. So computer B is a server providing service.

2- Create Project

Create Project RMITutorial
The classes packaged for Client and Server:
This is the working model of RMI. Server will register the object with Registry. Client will then look the Registry up  by IP address and Port, so that it can call methods from objects in Server.
  • Constants.java
package org.o7planning.tutorial.rmi;

public class Constants {

 
   public static final String LOCATION_HANOI = "HaNoi";    
   public static final String LOCATION_TOKYO = "Tokyo";
   public static final String LOCATION_CHICAGO = "Chicago";
   
   
 
   public static final String WEATHER_RAIN ="rain";
   
 
   public static final String WEATHER_SUNNY ="sunny";

}
  • WeatherData.java
package org.o7planning.tutorial.rmi;

import java.io.Serializable;
import java.util.Date;

public class WeatherData implements Serializable {

    private static final long serialVersionUID = 1L;

    private Date date;
    private String location;
    private String weather;

    public WeatherData(Date date, String location, String weather) {
        this.date = date;
        this.location = location;
        this.weather = weather;
    }

    public Date getDate() {
        return date;
    }

    public void setDate(Date date) {
        this.date = date;
    }

    public String getLocation() {
        return location;
    }

    public void setLocation(String location) {
        this.location = location;
    }

    public String getWeather() {
        return weather;
    }

    public void setWeather(String weather) {
        this.weather = weather;
    }

}
  • WeatherService.java
package org.o7planning.tutorial.rmi;

import java.rmi.Remote;
import java.rmi.RemoteException;
import java.util.Date;



public interface WeatherService extends Remote {
 
  // Method to retrieve weather information.
  public WeatherData getWeather(Date date, String location)
          throws RemoteException;
}
  • WeatherServiceImpl.java
package org.o7planning.tutorial.rmi.server;

import java.rmi.RemoteException;
import java.rmi.server.UnicastRemoteObject;
import java.util.Calendar;
import java.util.Date;

import org.o7planning.tutorial.rmi.Constants;
import org.o7planning.tutorial.rmi.WeatherData;
import org.o7planning.tutorial.rmi.WeatherService;

public class WeatherServiceImpl extends UnicastRemoteObject implements
       WeatherService {
   private static final long serialVersionUID = 1L;

   public WeatherServiceImpl() throws RemoteException {
       super();
   }

   @Override
   public synchronized WeatherData getWeather(Date date, String location)
           throws RemoteException {
       Calendar c = Calendar.getInstance();
       c.setTime(date);

       int dayOfWeek = c.get(Calendar.DAY_OF_WEEK);

       // Sunday, Monday
       if (dayOfWeek == 1 || dayOfWeek == 2) {
           if (location.equals(Constants.LOCATION_CHICAGO)) {
               // Rain
               return new WeatherData(date, location, Constants.WEATHER_RAIN);
           } else if (location.equals(Constants.LOCATION_HANOI)) {
               // Sunny
               return new WeatherData(date, location, Constants.WEATHER_SUNNY);
           } else if (location.equals(Constants.LOCATION_TOKYO)) {
               // Sunny
               return new WeatherData(date, location, Constants.WEATHER_SUNNY);
           }
           return new WeatherData(date, location, Constants.WEATHER_SUNNY);
       } else {
           return new WeatherData(date, location, Constants.WEATHER_SUNNY);
       }

   }
}
  • Client.java
package org.o7planning.tutorial.rmi.client;

import java.rmi.registry.LocateRegistry;
import java.rmi.registry.Registry;
import java.util.Date;

import org.o7planning.tutorial.rmi.Constants;
import org.o7planning.tutorial.rmi.WeatherData;
import org.o7planning.tutorial.rmi.WeatherService;

public class Client {

    // Host or IP of Server
    private static final String HOST = "localhost";
    private static final int PORT = 1099;
    private static Registry registry;

    public static void main(String[] args) throws Exception {

        // Search the registry in the specific Host, Port.
        registry = LocateRegistry.getRegistry(HOST, PORT);

        // Lookup WeatherService in the Registry.
        WeatherService service = (WeatherService) registry
                .lookup(WeatherService.class.getSimpleName());

        Date today = new Date();

        // Get Chicago weather info:
        WeatherData chicagoWeather = service.getWeather(today,
                Constants.LOCATION_CHICAGO);

        System.out.println("Chicago weather today: "
                + chicagoWeather.getWeather());
        
        // Get Hanoi weather info:
        WeatherData hanoiWeather = service.getWeather(today,
                Constants.LOCATION_HANOI);

        System.out.println("Hanoi weather today: " + hanoiWeather.getWeather());

    }
}
  • Server.java
package org.o7planning.tutorial.rmi.server;

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

import org.o7planning.tutorial.rmi.WeatherService;

public class Server {
   private static final int PORT = 1099;
   private static Registry registry;

   public static void startRegistry() throws RemoteException {
       // Create server registry
       registry =  LocateRegistry.createRegistry(PORT);
   }

   public static void registerObject(String name, Remote remoteObj)
           throws RemoteException, AlreadyBoundException {

       // Bind the object in the registry.
       // It is bind with certain name.
       // Client will lookup on the registration of the name to get object.        
       registry.bind(name, remoteObj);
       System.out.println("Registered: " + name + " -> "
               + remoteObj.getClass().getName() + "[" + remoteObj + "]");
   }

   public static void main(String[] args) throws Exception {
       System.out.println("Server starting...");
       startRegistry();
       registerObject(WeatherService.class.getSimpleName(), new WeatherServiceImpl());

       // Server was the start, and was listening to the request from the client.
       System.out.println("Server started!");
   }
}

3- Run Application

To run the RMI application, you need to pack your project into two jar files. The first jar file includes the classes to run in client machine. And second Jar file, including the classes to run in server machine.
This is the illustration:
However, you can run Demo on the Eclipse:
First run the class Server:
Server is running, and it registers Remote Object with the Registry. Next, you run class in Client.