Socket-Verbindung mit Java (Client-side)

Auf der Client-Seite bildet ein Telnet-Client das Gegenstück einer Verbindung zu dem Beispiel-Server. Der Telnet-Client lässt sich auf diese Art einsetzen, weil das Telnet-Protokoll lediglich Tastatureingaben vom Client zum Server bzw. Textausgaben vom Server zum Client überträgt.

public void startListening(int port, int backlog) throws IOException {
    // Start a passive socket, step (1a).
    ServerSocket passiveSocket = new ServerSocket(port, backlog);
    // Now the passive socket is listening.
    System.out.println("Server started on port " + port + ".");
    boolean listen = true;
    while(listen) {
        // Blocking wait for a connection.
        // If a client connects, a connection socket is returned
        // by the passive socket.
        Socket connectionSocket=passiveSocket.accept(); // step (1b+3)
        handleConnection(connectionSocket); // step (4)
        // Eventually, set boolean variable terminate.
        ...
    }
}

private void handleConnection(Socket connectionSocket) throws IOException {
    // Send a string to the client, step (4).
    OutputStream os = connectionSocket.getOutputStream();
    PrintWriter pw = new PrintWriter(os);
    pw.println("Tell me your name, please.");
    pw.flush(); // "Flushing" empties the send buffer.

    // Receive a string from the client, step (4).
    InputStream is = connectionSocket.getInputStream();
    BufferedReader br = new BufferedReader(new InputStreamReader(is));
    String name = br.readLine();
    if (name != null) {
        pw.println("Welcome " + name + "!");
        pw.flush();
    }
    // Close the connections.
    br.close();
    pw.close(); 
}

package networkprotocol;

import java.net.*;
import java.io.*;

public class Server {

    public void startListening(int port, int backlog) ... 
    private void handleConnection(Socket connectionSocket) ...

    public static void main(String[] args) {
        Server s = new Server();
        int port = 2005;
        int backlog = 100;
        try {
            s.startListening(port, backlog);
        } catch (IOException ioe) {
            System.out.println("There was an exception, the message is: " + ioe.getMessage());
        }
    }
}

[stein@webis stein]$
[stein@webis stein]$ telnet localhost 2005
Trying 127.0.0.1...
Connected to localhost (127.0.0.1).
Escape character is ’ˆ]’.
Tell me your name, please.
Benno
Welcome Benno!
Connection closed by foreign host.
[stein@webis stein]$