Server.java

import java.io.File;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.Socket;
import java.util.ArrayList;

import java.net.ServerSocket;

/*
 * A chat server that delivers public and private messages and files.
 */
public class Server {

	// The server socket.
	private static ServerSocket serverSocket = null;
	// The client socket.
	private static Socket clientSocket = null;

	public static ArrayList<clientThread> clients = new ArrayList<clientThread>();

	public static void main(String args[]) {

		// The default port number.
		int portNumber = 1234;


		if (args.length < 1) 
		{

			System.out.println("No port specified by user.\nServer is running using default port number=" + portNumber);

		} 
		else 
		{
			portNumber = Integer.valueOf(args[0]).intValue();

			System.out.println("Server is running using specified port number=" + portNumber);
		}

		/*
		 * Open a server socket on the portNumber (default 1234).
		 */
		try {
			serverSocket = new ServerSocket(portNumber);
		} catch (IOException e) {
			System.out.println("Server Socket cannot be created");
		}

		/*
		 * Create a client socket for each connection and pass it to a new client
		 * thread.
		 */

		int clientNum = 1;
		while (true) {
			try {

				clientSocket = serverSocket.accept();
				clientThread curr_client =  new clientThread(clientSocket, clients);
				clients.add(curr_client);
				curr_client.start();
				System.out.println("Client "  + clientNum + " is connected!");
				clientNum++;

			} catch (IOException e) {

				System.out.println("Client could not be connected");
			}


		}

	}
}

/*
 * This client thread class handles individual clients in their respective threads 
 * by opening a separate input and output streams. 
 */
class clientThread extends Thread {

	private String clientName = null;
	private ObjectInputStream is = null;
	private ObjectOutputStream os = null;
	private Socket clientSocket = null;
	private final ArrayList<clientThread> clients;
	public clientThread(Socket clientSocket, ArrayList<clientThread> clients) {

		this.clientSocket = clientSocket;
		this.clients = clients;

	}


	public void run() {

		ArrayList<clientThread> clients = this.clients;

		try {
			/*
			 * Create input and output streams for this client.
			 */
			is = new ObjectInputStream(clientSocket.getInputStream());
			os = new ObjectOutputStream(clientSocket.getOutputStream());

			String name;
			while (true) {

				synchronized(this)
				{
					this.os.writeObject("Please enter your name :");
					this.os.flush();
					name = ((String) this.is.readObject()).trim();

					if ((name.indexOf('@') == -1) || (name.indexOf('!') == -1)) {
						break;
					} else {
						this.os.writeObject("Username should not contain '@' or '!' characters.");
						this.os.flush();
					}
				}
			}

				/* Welcome the new the client. */

				System.out.println("Client Name is " + name); 

				this.os.writeObject("*** Welcome " + name + " to our chat room ***\nEnter /quit to leave the chat room");
				this.os.flush();

				this.os.writeObject("Directory Created");
				this.os.flush();
				synchronized(this)
				{

				for (clientThread curr_client : clients)  
				{
					if (curr_client != null && curr_client == this) {
						clientName = "@" + name;
						break;
					}
				}

				for (clientThread curr_client : clients) {
					if (curr_client != null && curr_client != this) {
						curr_client.os.writeObject(name + " has joined");
						curr_client.os.flush();

					}

				}
			}

			/* Start the conversation. */

			while (true) {

				this.os.writeObject("Please Enter command:");
				this.os.flush();

				String line = (String) is.readObject();


				if (line.startsWith("/quit")) {

					break;
				}

				/* If the message is private sent it to the given client. */

				if (line.startsWith("@")) {

					unicast(line,name);        	

				}

				/* If the message is blocked from a given client. */

				else if(line.startsWith("!"))
				{
					blockcast(line,name);
				}

				else 
				{

					broadcast(line,name);

				}

			}

			/* Terminate the Session for a particluar user */

			this.os.writeObject("*** Bye " + name + " ***");
			this.os.flush();
			System.out.println(name + " disconnected.");
			clients.remove(this);


			synchronized(this) {

				if (!clients.isEmpty()) {

					for (clientThread curr_client : clients) {


						if (curr_client != null && curr_client != this && curr_client.clientName != null) {
							curr_client.os.writeObject("*** The user " + name + " disconnected ***");
							curr_client.os.flush();
						}




					}
				}
			}


			this.is.close();
			this.os.close();
			clientSocket.close();

		} catch (IOException e) {

			System.out.println("User Session terminated");

		} catch (ClassNotFoundException e) {

			System.out.println("Class Not Found");
		}
	}



	/**** This function transfers message or files to all the client except a particular client connected to the server ***/	

	void blockcast(String line, String name) throws IOException, ClassNotFoundException {

		String[] words = line.split(":", 2);

		/* Transferring a File to all the clients except a particular client */

		if (words[1].split(" ")[0].toLowerCase().equals("sendfile"))
		{
			byte[] file_data = (byte[]) is.readObject();

			synchronized(this) {
				for (clientThread curr_client : clients) {
					if (curr_client != null && curr_client != this && curr_client.clientName != null
							&& !curr_client.clientName.equals("@"+words[0].substring(1)))
					{
						curr_client.os.writeObject("Sending_File:"+words[1].split(" ",2)[1].substring(words[1].split("\\s",2)[1].lastIndexOf(File.separator)+1));
						curr_client.os.writeObject(file_data);
						curr_client.os.flush();


					}
				}

				/* Echo this message to let the user know the blocked file was sent.*/

				this.os.writeObject(">>Blockcast File sent to everyone except "+words[0].substring(1));
				this.os.flush();
				System.out.println("File sent by "+ this.clientName.substring(1) + " to everyone except " + words[0].substring(1));
			}
		}

		/* Transferring a message to all the clients except a particular client */

		else 
		{
			if (words.length > 1 && words[1] != null) {
				words[1] = words[1].trim();
				if (!words[1].isEmpty()) {
					synchronized (this){
						for (clientThread curr_client : clients) {
							if (curr_client != null && curr_client != this && curr_client.clientName != null
									&& !curr_client.clientName.equals("@"+words[0].substring(1))) {
								curr_client.os.writeObject("<" + name + "> " + words[1]);
								curr_client.os.flush();


							}
						}
						/* Echo this message to let the user know the blocked message was sent.*/

						this.os.writeObject(">>Blockcast message sent to everyone except "+words[0].substring(1));
						this.os.flush();
						System.out.println("Message sent by "+ this.clientName.substring(1) + " to everyone except " + words[0].substring(1));
					}
				}
			}
		}
	}

	/**** This function transfers message or files to all the client connected to the server ***/

	void broadcast(String line, String name) throws IOException, ClassNotFoundException {

		/* Transferring a File to all the clients */

		if (line.split("\\s")[0].toLowerCase().equals("sendfile"))
		{

			byte[] file_data = (byte[]) is.readObject();
			synchronized(this){
				for (clientThread curr_client : clients) {
					if (curr_client != null && curr_client.clientName != null && curr_client.clientName!=this.clientName) 
					{
						curr_client.os.writeObject("Sending_File:"+line.split("\\s",2)[1].substring(line.split("\\s",2)[1].lastIndexOf(File.separator)+1));
						curr_client.os.writeObject(file_data);
						curr_client.os.flush();

					}
				}

				this.os.writeObject("Broadcast file sent successfully");
				this.os.flush();
				System.out.println("Broadcast file sent by " + this.clientName.substring(1));
			}
		}

		else
		{
			/* Transferring a message to all the clients */

			synchronized(this){

				for (clientThread curr_client : clients) {

					if (curr_client != null && curr_client.clientName != null && curr_client.clientName!=this.clientName) 
					{

						curr_client.os.writeObject("<" + name + "> " + line);
						curr_client.os.flush();

					}
				}

				this.os.writeObject("Broadcast message sent successfully.");
				this.os.flush();
				System.out.println("Broadcast message sent by " + this.clientName.substring(1));
			}

		}

	}

	/**** This function transfers message or files to a particular client connected to the server ***/	

	void unicast(String line, String name) throws IOException, ClassNotFoundException {

		String[] words = line.split(":", 2); 

		/* Transferring File to a particular client */

		if (words[1].split(" ")[0].toLowerCase().equals("sendfile"))
		{
			byte[] file_data = (byte[]) is.readObject();

			for (clientThread curr_client : clients) {
				if (curr_client != null && curr_client != this && curr_client.clientName != null
						&& curr_client.clientName.equals(words[0]))
				{
					curr_client.os.writeObject("Sending_File:"+words[1].split(" ",2)[1].substring(words[1].split("\\s",2)[1].lastIndexOf(File.separator)+1));
					curr_client.os.writeObject(file_data);
					curr_client.os.flush();
					System.out.println(this.clientName.substring(1) + " transferred a private file to client "+ curr_client.clientName.substring(1));

					/* Echo this message to let the sender know the private message was sent.*/

					this.os.writeObject("Private File sent to " + curr_client.clientName.substring(1));
					this.os.flush();
					break;

				}
			}
		}

		/* Transferring message to a particular client */

		else
		{

			if (words.length > 1 && words[1] != null) {

				words[1] = words[1].trim();


				if (!words[1].isEmpty()) {

					for (clientThread curr_client : clients) {
						if (curr_client != null && curr_client != this && curr_client.clientName != null
								&& curr_client.clientName.equals(words[0])) {
							curr_client.os.writeObject("<" + name + "> " + words[1]);
							curr_client.os.flush();

							System.out.println(this.clientName.substring(1) + " transferred a private message to client "+ curr_client.clientName.substring(1));

							/* Echo this message to let the sender know the private message was sent.*/

							this.os.writeObject("Private Message sent to " + curr_client.clientName.substring(1));
							this.os.flush();
							break;
						}
					}
				}
			}
		}
	}


}