在哪种情况下可以在DatagramSocket中使用getPort（）？

Question

I'm using DatagramSockets to build a application and I stacked in a point of the code that I should identify which port my socket was bound. So in this part of my code:

        dnsConnection = new DatagramSocket();

        byte[] date = "\nSend me a available server IP!".getBytes();
        pkg = new DatagramPacket(date, date.length, addr, port);

        status.append("\nTrying to send the message to: " + addr.getHostAddress());

        dnsConnection.send(pkg);
        localPort = dnsConnection.getPort();

        status.append("\nRequest has been sent to: " + addr.getHostAddress());
        status.append("\nthrough the port: " + localPort);

As you can see, I'm trying to get the port in which my socket was bound using the method getPort() . Reading the API, we have this statement:

public int getPort()

Returns the port number to which this socket is connected. Returns -1 if the socket is not connected.

In this sense I continue to search an alternative and I found the method getLocalPort() and in the API:

public int getLocalPort()

Returns the port number on the local host to which this socket is bound.

Then using getLocalPort() I could have gotten the port in which my socket is bind, and I understood that getPort() is probably to get the port that the socket is connected, ie, the port of the host in which I want to send information. After all this, grew up a question on my head:

As UDP is conectionless, in which moment can I use getPort() to recovery the port in which my socket is connected?

Maybe I understood wrong and getPort() is not related with the remote host, if I'm wrong please clarify-me.

That is. Thanks. Pablo

Answer 1

When you call dnsConnection.send(pkg), the DatagramPacket pkg includes information of the IP address of the remote host, and the port number on the remote host. When you later call dnsConnection.getPort(), it just returns the remote port number of the last sent packet, which is local information.