Client side socket isn't creating (ConnectException)

Question

I have two machines with hostname q2 and w18 and I have a two simple program to send some message between these machines using socket. I have one file.cfg which contains the ip needs to be used by both Client.java and Server.java .

Client

public class Client {
    public static void main(String... C) {
        try {

            String filePath = "file.cfg";
            String ip = "";

            byte[] bytes = Files.readAllBytes(Paths.get(filePath));
            ip = new String(bytes);
            ip = ip.trim();

            System.out.println("cfg file contains " + ip);

            Socket so = new Socket(ip, 3112);
            System.out.println("socket Connected. " + so.toString());

            so.setSoTimeout(30000);
            BufferedReader reader = new BufferedReader(
                    new InputStreamReader(so.getInputStream(), StandardCharsets.UTF_8));
            System.out.println(reader.readLine());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Server

public class Server {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = null;

        try {
            String filePath = "file.cfg";
            String ip = "";

            byte[] bytes = Files.readAllBytes(Paths.get(filePath));
            ip = new String(bytes);
            ip = ip.trim();

            System.out.println("cfg file contains" + ip);

            serverSocket = new ServerSocket(3112, 50, InetAddress.getByName(ip));
            System.out.println("Server Socket is created. " + serverSocket.toString());
        } catch (IOException ex) {
            ex.printStackTrace();
        }

        Socket socket = null;

        try {
            System.out.println("Waiting for Accept...");
            socket = serverSocket.accept();
            System.out.println("Accepted...");


            OutputStreamWriter localOut = new OutputStreamWriter(socket.getOutputStream());

            localOut.write("Hi,");
            localOut.write("Hello");
            localOut.write("\n");
            localOut.flush();
            localOut.close();

        } catch (Exception ex) {
            ex.printStackTrace();
        }
        socket.close();
        serverSocket.close();
    }
}

file.cfg

10.90.50.101
# this ip will be similar in both machines
# for ref, 
# 10.90.50.101 -> q2 and 
# 10.90.50.102 -> w18

Success Scenarios

1. I ran both Client and Server in w18 , which works fine
2. I ran both Client and Server in q2 which works fine
3. I ran Client in q2 and Server in w18 which works fine

Failure Scenario

1. When I ran Server in q2 and Client in w18 . Client Socket isn't creating at all. Client throwing below error after some time while creating a socket.

java.net.ConnectException: Connection timed out (Connection timed out)
        at java.net.PlainSocketImpl.socketConnect(Native Method)
        at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
        at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
        at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
        at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
        at java.net.Socket.connect(Socket.java:589)
        at java.net.Socket.connect(Socket.java:538)
        at java.net.Socket.<init>(Socket.java:434)
        at java.net.Socket.<init>(Socket.java:211)
        at Client.main(Client.java:21)

Question

I've seen some ConnectException SO's QA's, But here I'm able to achieve the point 3 in Success Scenarios but not able to do the same thing vice versa which is point 1 of Failure Scenario .

Answer 1

in server.java try replacing below code

 serverSocket = new ServerSocket(3112, 50, InetAddress.getByName(ip));

with

serverSocket = new ServerSocket(3112, 50, "localhost");

serverSocket = new ServerSocket(3112, 50, "127.0.0.1");

serverSocket = new ServerSocket(3112, 50, "0.0.0.0");