Network discovery in Java using multicasting

java networking discovery
mohi666 picture mohi666 · Jul 15, 2010 · Viewed 17k times · Source

I'm trying to make a client/server Java App. Both client and server will be running on the same wi-fi network. Server will be running on a specific port that client is aware of.

I am planning to send a multicast message from client through the network for that specific port to discover the server. However, I'm not too sure how I can find out which IP in my network received my message.

Do I need to create a socket on the client and listen to incoming packets once I send my multicast message in case server replies back?

Thanks in advance.

Answer

irreputable picture irreputable · Jul 15, 2010

(1)server listens on a pre-arranged port 

DatagramSocket s = new DatagramSocket(8888);
s.receive  //(1)
s.send     //(2)

(3)client sends a message to the port, on the broadcast IP, 255.255.255.255

DatagramSocket c = new DatagramSocket();
c.send(255.255.255.255:8888,msg)     //(3)
c.receive  //(4)

the client binds to a port too. we didn't specify it, so it's random chosen for us.

(3) will broadcast the message to all local machines, server at (1) receives message, with the client IP:port.

(2) server sends response message to client IP:port

(4) client gets the reponse message from server.

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