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import java.net.DatagramPacket;
import java.net.DatagramSocket;
/**
* This program waits to receive datagrams sent the specified port. When it
* receives one, it displays the sending host and prints the contents of the
* datagram as a string. Then it loops and waits again.
*/
public class UDPReceive {
public static final String usage = "Usage: java UDPReceive <port>";
public static void main(String args[]) {
try {
if (args.length != 1)
throw new IllegalArgumentException("Wrong number of args");
// Get the port from the command line
int port = Integer.parseInt(args[0]);
// Create a socket to listen on the port.
DatagramSocket dsocket = new DatagramSocket(port);
// Create a buffer to read datagrams into. If anyone sends us a
// packet containing more than will fit into this buffer, the
// excess will simply be discarded!
byte[] buffer = new byte[2048];
// Create a packet to receive data into the buffer
DatagramPacket packet = new DatagramPacket(buffer, buffer.length);
// Now loop forever, waiting to receive packets and printing them.
for (;;) {
// Wait to receive a datagram
dsocket.receive(packet);
// Decode the bytes of the packet to characters, using the
// UTF-8 encoding, and then display those characters.
String msg = new String(buffer, 0, packet.getLength(), "UTF-8");
System.out.println(packet.getAddress().getHostName() + ": " + msg);
// Reset the length of the packet before reusing it.
// Prior to Java 1.1, we'd just create a new packet each time.
packet.setLength(buffer.length);
}
} catch (Exception e) {
System.err.println(e);
System.err.println(usage);
}
}
}
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