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Invocation de méthode à distance en Java

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1- Introduction

RMI est un moyen pour vous d'appeler une méthode à distance. Par exemple, appeler une méthode exécutée sur un ordinateur B et recevoir la réponse finale. L'ordinateur B est ainsi un service de fourniture de serveur.

2- Créer un projet

Créer un nouveau projet baptisé RMITutorial
Les classes emballées pour Client et Server
C'est le modèle de travail de RMI. Le serveur enregistrera l'objet avec l'enregistrement (Registry). Le client cherche alors l'enregistrement par adresse IP et Port (Host + Port), afin qu'il puisse appeler des méthodes (method) à partir d'objets dans Serveur.
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- Exécuter l'application

Để chạy được ứng dụng trên bạn cần đóng gói project thành 2 file jar. File jar 1 gồm các class dùng để chạy ứng dụng tại client. Và file jar 2 bao gồm các class để chạy ứng dụng tại server.
Pour exécuter l'application RMI, vous devez emballer votre projet dans deux fichiers jar. Le premier fichier jar comprend des classes à exécuter dans la machine cliente. Et le second fichier jar comprend des classes à exécuter dans la machine serveur.
C'est l'illustration:
Cependant vous pouvez exécuter la démo (demo) sur Eclipse:
D'abord, exécuter la classe Server:
Server starting...
Registered: WeatherService -> org.o7planning.tutorial.rmi.server.WeatherServiceImpl[WeatherServiceImpl[UnicastServerRef [liveRef: [endpoint:[192.168.0.102:64865](local),objID:[6aadac58:179707abf4c:-7fff, -728182817779393915]]]]]
Server started!
Le serveur est en cours d'exécution et il enregistre Remote Object avec l'enregistrement (Registry). Ensuite, vous exécutez la classe dans Client.
Chicago weather today: sunny
Hanoi weather today: sunny

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