How do I create a simple Datagram server?

Created May 4, 2012

Tim Rohaly

To create a server with UDP, do the following:

Create a DatagramSocket attached to a port.

int port = 1234;
DatagramSocket socket = new DatagramSocket(port);

Allocate space to hold the incoming packet, and create an instance of DatagramPacket to hold the incoming data.
```
byte[] buffer = new byte[1024];
DatagramPacket packet =
       new DatagramPacket(buffer, buffer.length);
```

Block until a packet is received, then extract the information you need from the packet.

// Block on receive()
socket.receive(packet);

// Find out where packet came from
// so we can reply to the same host/port
InetAddress remoteHost = packet.getAddress();
int         remotePort = packet.getPort();

// Extract the packet data
byte[]      data       = packet.getData();

The server can now process the data it has received from the client, and issue an appropriate reply in response to the client's request.

The full source for a UDP echo server and client can be downloaded from the following links: