前面廢話過了，現在就直接看程式碼吧！

ThreadedClient.java

package exercise01;
import java.io.*;
import java.net.*;

public class ThreadedClient {
    private String hostname;
    private int port;
    Socket socket = null;
    
    public ThreadedClient(String hostname, int port){
    	//constructor of the Client class
    	this.hostname = hostname;
    	this.port = port;
    }
    
    public void connect() throws UnknownHostException, IOException{
    	System.out.println("Attempting connect to "+ hostname +":"+port);
    	socket = new Socket(hostname,port);
    	System.out.println("Connection established!");
    }
    
    public void readResponse() throws IOException{
    	String userInput;
    	BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
    	System.out.println("Response from the server:");
    	while((userInput = reader.readLine() )!= null ){
    		System.out.println(userInput);
    	}
    }
    
    public void askForTime() throws IOException{
    	BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
    	writer.write("Time?");
    	writer.newLine();
    	writer.flush();
    }
    
    public static void main(String[] argv){
    	//create an object for the current class Client
    	ThreadedClient client = new ThreadedClient("localhost",8181);
    	try{
    		//trying to establish a connection to the server
    		client.connect();
    		
    		//ask the server for time
    		client.askForTime();
    		
    		//if connection succeed, return the input contents
    		client.readResponse();
    		
    	}catch(UnknownHostException ukhe){
    		//if the host not found
    		System.err.println("Host unknown! Connection can not be established!");
    	}catch(IOException ioe){
    		//if the server doesn't work
    		System.err.println("Connection can not be established! The server may not be on! Check the error message! "+ioe.getMessage());
    	}
    }
    
    
}
 

package exercise01;
import java.io.*;
import java.net.*;
import java.util.Date;

public class ThreadedServer {
	private ServerSocket serverSocket;
	private int port;
	
	public ThreadedServer(int port){
		this.port = port;
	}
	
	//get the thread started
	public void start() throws IOException{
		System.out.println("Starting the server at the port: "+ port);
		serverSocket = new ServerSocket(port);
		
		//instantial an object client
		Socket client = null;
		
		//set the condition to be true for endless loops
		while(true){
			System.out.println("Waiting for clients...");
			client = serverSocket.accept();
			System.out.println("The following client has connected: " + client.getInetAddress().getCanonicalHostName());
			//A client has connected to the server
			Thread thread = new Thread(new SocketClientHandler(client));
			thread.start();
		}
	}
	
	/**
	 * instantial an object of class ThreadedServer and start the server
	 * 
	 * @param argv
	 */
	public static void main(String[] argv){
		//set the default port number
		int port = 8181;
		
		try{
			//initializing the socket server
			ThreadedServer threadedServer = new ThreadedServer(port);
			threadedServer.start();
		}catch(IOException ioe){
			ioe.printStackTrace();
		}
	}
}

class SocketClientHandler implements Runnable{

	private Socket client;
	
	public SocketClientHandler(Socket client){
		this.client = client;
	}
	
	/**
	 * get the thread started by the run method
	 */
	@Override
	public void run() {
		try{
			System.out.println("Thread started with name: " + Thread.currentThread().getName());
			readResponse();
		}catch(IOException ioe){
			ioe.printStackTrace();
		}catch(InterruptedException ie){
			ie.printStackTrace();
		}
	}

	/**
	 * read the response from the server
	 * @throws IOException
	 * @throws InterruptedException
	 */
	private void readResponse() throws IOException, InterruptedException {
		String userInput;
		BufferedReader reader = new BufferedReader(new InputStreamReader(client.getInputStream()));
		while(( userInput = reader.readLine())!= null){
			if(userInput.equals("Time?")){
				System.out.println("Request to send time! Sending time current.");
				sendTime();
				break;
			}
		}
	}

	/**
	 * send the current time to the server
	 * @throws IOException
	 * @throws InterruptedException
	 */
	private void sendTime() throws IOException, InterruptedException {
		BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(client.getOutputStream()));
		writer.write(new Date().toString());
		writer.flush();
		writer.close();
	}
	
}