CODEWITHSUNDEEP
javaandroidsocketstcpconnection
lunalcni
lunalcni

Reputation: 142

tcp connection between Android server and PC client

Server part(Android)

new Thread(new Runnable() {
            public void run() {
                DatagramSocket s;

                try {
                    s = new DatagramSocket();
                    s.send(new DatagramPacket("aaa".getBytes(), 3, InetAddress.getByName(/* Server ip address*/), 11720));
                    s.close();
                } catch (UnknownHostException e1) {
                    // TODO Auto-generated catch block
                    e1.printStackTrace();
                } catch (IOException e1) {
                    // TODO Auto-generated catch block
                    e1.printStackTrace();
                }



                while(true)
                {
                try {
                    ServerSocket ssocket = new ServerSocket(11720);
                    ssocket.accept(); // Cannot make connection!!

                    Toast.makeText(a, "Who's coming", Toast.LENGTH_SHORT).show();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                }
            }
        }).start();

Client code (Java, PC)

public static void main(String[] args) {
    try {
        DatagramSocket ds = new DatagramSocket(11720);
        DatagramPacket dp = new DatagramPacket(new byte[1024], 1024);
        ds.close();

        try {
            ds.receive(dp);

            // ds.send(new DatagramPacket("aaaa".getBytes(), 4, dp.getAddress(), 11720));
            Socket socket = new Socket(dp.getAddress(), 11720); // Cannot make connection!!
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }


    } catch (SocketException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}

I want to make connection between android server and pc client. First android send a packet to pc. I think server can know using this packet, so I use function getAddress().

Then android open socket using port number 11720 and pc try to connect android. But it cannot connect.

Why this code cannot make connection?

Oh, I just want to know how can I connect from pc to phone. So I change pc and android code.

Firstly, my goal is connect to android using static port(11720). But I cannot make connection using static port when using LTE.

So I check socket information using simple program.

This is in pc.

public static void main(String[] args) {
    try {
        DatagramSocket ds = new DatagramSocket(11720);
        DatagramPacket dp = new DatagramPacket(new byte[1024], 1024);

        while (true)
        {
            ds.receive(dp);
            System.out.println(dp.getSocketAddress());
        }

    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }



}

And this is in android.

new Thread(new Runnable() {
            public void run() {
                try {
                    DatagramSocket s = new DatagramSocket(11720);
                    while(true)
                    {
                        s.send(new DatagramPacket("aaa".getBytes(), 3, InetAddress.getByName("143.248.55.131" /* Server address */), 11720));
                    }

                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }).start();

I execute programs using WiFi and LTE. And result is

/143.248.56.118:11720 <- using WiFi
/143.248.56.118:11720
/143.248.56.118:11720
/117.111.7.124:35645 <- change LTE
/117.111.7.124:35645
/117.111.7.124:35645

When using LTE, socket's port number is changed. so I cannot send packet using static port number.

How can I solve this problem?

Upvotes: 0

Views: 867

Answers (1)

Kunjan Thadani
Kunjan Thadani

Reputation: 1670

Firstly, why are you complicating by using Datagram Socket unnecessarily? You can simply use TCP without any problems.

Well, your client code(Java PC) might be waiting at:

ds.receive(dp);

And so the socket might not get created.

Although the android program is sending a packet but UDP being unreliable, the packet may not be received by the client code. Also, this can be due to network issues like both cannot get a connection, or there might be a NAT between them which would not let any UDP packet to let in.

So, I would suggest to simply use TCP. Don't complicate by first sending a UDP packet and then connecting with TCP.

Upvotes: 1

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