server.java

用java实现的投票系统

import java.rmi.*;
import java.rmi.server.*;
import java.util.*;
import java.util.concurrent.Semaphore;
import java.rmi.registry.*;
public class Server extends UnicastRemoteObject implements Serverinterface{
	 private static Semaphore semaphore=new Semaphore(1); // to make the syncronized update
    // vector for store list of callback objects
    private static Vector callbackObjects;
    private static int count1=0; //record the number of "yes"
    private static int count2=0; //record the number of "no"
    private static int count3=0; //record the number of "do not care"
    public Server() throws RemoteException {
      super();
      // instantiate a Vector object for storing callback objects
      callbackObjects = new Vector();
    }
    
    // do recording
    public void update(String m){
    	try {
    	semaphore.acquire();	
    	if(m.equals("1")) this.count1++;
    	if(m.equals("2")) this.count2++;
    	if(m.equals("3")) this.count3++;
    	}
    	catch(InterruptedException ex){
    	}
    	finally{
    		semaphore.release();
    	}
    	
    }
    
    // method for client to call to add itself to its callback
    public void addCallback(Callbackinterface CallbackObject) {
       // store the callback object into the vector
        System.out.println("Server got an 'addCallback' call.");
       callbackObjects.addElement (CallbackObject);
    } 

   private static void startRegistry(int RMIPortNum)
        throws RemoteException{
    try {
	 Registry registry= LocateRegistry.getRegistry(RMIPortNum);
	 registry.list( );  
		   // The above call will throw an exception
        // if the registry does not already exist
}
catch (RemoteException ex) {
  // No valid registry at that port.
      System.out.println(
      "RMI registry cannot be located at port " + RMIPortNum);
      Registry registry= LocateRegistry.createRegistry(RMIPortNum);
      System.out.println( "RMI registry created at port " + RMIPortNum);
}
} // end startRegistry
    

    
    private static void callback( ) {
    // the server calls the clients in the list   	
    
     for (int i = 0; i < callbackObjects.size(); i++)  {
       System.out.println("Now performing the "+ i +"th callback\n");    
       // convert the vector object to a callback object
       Callbackinterface client = 
           (Callbackinterface) callbackObjects.elementAt(i);
        try{
       client.callMe ( "Server calling back to client " + i);
       }
       catch(Exception ex){
       }
     }
}//end callback

    
    public static void main(String args[]) {
    try{
        Serverinterface obj = new Server();
          startRegistry(1099);
          Registry registry = LocateRegistry.getRegistry();
          registry.rebind("Server", obj);
          System.out.println("Server " + obj + " registered");
          
      //    callback( );
    }
    catch(Exception ex){
    	 ex.printStackTrace();

    }
    } // end main
   
}