ServerSocket

In this chapter you will learn:

How to use ServerSocket to create a server
Local Port Scanner

ServerSocket is for server

ServerSocket is for servers. The Socket class is for clients.

import java.io.IOException;
import java.net.ServerSocket;
//  j a v  a 2  s. c  o  m
public class MainClass {

  public static void main(String[] args) {

    try {
      ServerSocket server = new ServerSocket(0);
      System.out.println("This server runs on port " + 
                   server.getLocalPort());
    } catch (IOException ex) {
      System.err.println(ex);
    }
  }
}

Local Port Scanner

import java.io.IOException;
import java.net.ServerSocket;
//  ja v  a  2s .  c om
public class MainClass {

  public static void main(String[] args) {

    for (int port = 1; port <= 65535; port++) {

      try {
        // the next line will fail and drop into the catch block if
        // there is already a server running on the port
        ServerSocket server = new ServerSocket(port);
      } catch (IOException ex) {
        System.out.println("There is a server on port " + port + ".");
      }
    }
  }
}