Java Networking “Connection Refused: Connect”

Question

I have been trying to get a simple networking test program to run with no results.

Server:

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

public class ServerT         


        

Answer 1

These problem comes under the following situations:

1. Client and Server, either or both of them are not in network.

2. Server is not running.

3. Server is running but not listening on port, client is trying to connect.

4. Firewall is not permitted for host-port combination.

5. Host Port combination is incorrect.

6. Incorrect protocol in Connecting String.

How to solve the problem:

1. First you ping destination server. If that is pinging properly, then the client and server are both in network.

2. Try connected to server host and port using telnet. If you are able to connect with it, then you're making some mistakes in the client code.

Answer 2

For what it's worth, your code works fine on my system.

I hate to say it, but it sounds like a firewall issue (which I know you've already triple-checked) or a Comcast issue, which is more possible than you might think. I'd test your ISP.

Answer 3

Likely the server socket is only being bound to the localhost address. You can bind it to a specific IP address using the 3-argument form of the constructor.

Answer 4

I had the same problem because sometimes the client started before server and, when he tried to set up the connection, it couldn't find a running server.

My first (not so elegant) solution was to stop the client for a while using the sleep method:

try {
   Thread.sleep(1000);
} 
catch (InterruptedException e) {
   e.printStackTrace();
}

I use this code just before the client connection, in your example, just before Socket sock = new Socket(HOSTNAME, PORT_NUMBER);

My second solution was based on this answer. Basically I created a method in the client class, this method tries to connect to the server and, if the connection fails, it waits two seconds before retry. This is my method:

private Socket createClientSocket(String clientName, int port){

    boolean scanning = true;
    Socket socket = null;
    int numberOfTry = 0;

    while (scanning && numberOfTry < 10){
        numberOfTry++;
        try {
            socket = new Socket(clientName, port);
            scanning = false;
        } catch (IOException e) {
            try {
                Thread.sleep(2000);
            } catch (InterruptedException ie) {
                ie.printStackTrace();
            }
        }

    }
    return socket;
}

As you can see this method tries to create a socket for ten times, then returns a null value for socket, so be carefull and check the result.

Your code should become:

Socket sock = createClientSocket(HOSTNAME, PORT_NUMBER);
if(null == sock){ //log error... }

This solution helped me, I hope it helps you as well. ;-)

Answer 5

I assume you are using a Router to connect to Internet. You should do Port Forwarding to let public access your internal network. Have a look at How do you get Java sockets working with public IPs?

I have also written a blog post about Port forwarding, you might wanna have a look :) http://happycoders.wordpress.com/2010/10/03/how-to-setup-a-web-server-by-yourself/

But I still couldn't get this accessed over public IP, working on it now...