TCP / IP的NTP（服务器-客户端）

Question

i have a simple server...

public static void main(String[] args) throws Exception{
    ServerSocket server = new ServerSocket(2000);
    Socket sock = server.accept();
    InputStream  in = sock.getInputStream();
    OutputStream out = sock.getOutputStream();
    PrintWriter w = new PrintWriter(out);
    Scanner s = new Scanner(in);
    ...

and a simple client...

public static void main(String[] args) throws Exception{
    Socket sock = new Socket("localhost",2000);;
    InputStream in= sock.getInputStream();
    OutputStream out = sock.getOutputStream();
    PrintWriter w  = new PrintWriter(out);
    Scanner s = new Scanner(in);
    ....

-how can i connect more clients to this server? (I need 2 more) -also i want to send system time from server to clients and then clients will send back their time 10 times each plus some fixed delay (0.5-1 sec) then the server must find the average from all delays and send it back to the clients as the new time...

thank you for your time...

Answer 1

System.currentTimeMillis() provides the system time

Every Socket returned by server.accept() is a separate object and your server can communicate independently with each client through each Socket object. However, since your application is time-sensitive, I would recommend using a separate thread for each client.

A simple server would be:

ServerSocket serverSock = new ServerSocket(2000);

while (true)
{
    Socket fpSock = serverSock.accept();
    MyThread t = new MyThread(fpSock, this);
    t.start();
}

The processing you need will be done in the MyThread run() method. "this" is passed to the thread to provide a reference where each thread can callback to methods in the main class. Make sure to make such methods synchronized .

You also don't necessarily need to send the server's time to the client, simply send a generic packet which the client is expected to echo back. Use the server's timestamp for all transactions to avoid variation in client system time.