android - java.net.ConnectException: failed to connect to /192.168.253.3 (port 2468): connect failed: ECONNREFUSED (Connection refused)

Question

I want to transfer some data between PC and a mobile phone with WiFi.

This is how I get the WiFi IP address:

String ip  = String.format(
                    "%d.%d.%d.%d",
                    (wifiInfo.getIpAddress() & 0xff),
                    (wifiInfo.getIpAddress() >> 8 & 0xff),
                    (wifiInfo.getIpAddress() >> 16 & 0xff),
                    (wifiInfo.getIpAddress() >> 24 & 0xff));

new Recive().execute(ip);

This is the code about sending a message to the PC:

Socket socket = null;
String message = "test
";
protected Void doInBackground(String... urls) {
    try {
        Log.i("ip", urls[0]);
        socket = new Socket(urls[0], 2468);
        toserver = new DataOutputStream(socket.getOutputStream());
        toserver.writeBytes(message);

        toserver.flush();
        toserver.close();
        socket.close();
        return null;
    } catch (Exception e) {
        Log.i("e", e.toString());
        return null;
    }
}

But an error occurs,

java.net.ConnectException: failed to connect to /192.168.253.3 (port 2468): connect failed: ECONNREFUSED (Connection refused)

Besides, I use a android phone to run the app.

Answer 1

A connect failed: ECONNREFUSED (Connection refused) most likely means that there is nothing listening on that port AND that IP address. Possible explanations include:

• the service has crashed or hasn't been (successfully!) started,
• your client is trying to connect using the wrong IP address or port,
• your client is trying to connect using a DNS name that resolves to the wrong IP, or
• server access is being blocked by a firewall that is "refusing" on the server/service's behalf. This is pretty unlikely given that normal practice (these days) is for firewalls to "blackhole" all unwanted connection attempts.

---

Note that while you have an array variable called urls, it cannot contain real URLs. There is no overload of the Socket constructor that takes a real URL in any form. Indeed, if you supplied a URL in string form like this:

 new Socket("http://example.com", 42)

the result would be a different exception. Likewise, if you attempt to connect to an IP address on a network that you can't route to (e.g. "a different WiFi network"), then you will get a different exception; e.g. "host not found", "no route to host" or "no route to network".