• Convert the data into byte array.
• Pass this byte array, the length of the data array,the InetAddress and port to target  DatagramPacket() constructor.
• Next create a DatagramSocket and pass the packet to its send() method
• Example:
  try {
  InetAddress intaddr = new InetAddess("intaddr.ABC.com");
  int n1 = 40;
  String str1 = "My second UDP Packet"
  byte[] bt1 = str1.getBytes();
  DatagramPacket dp = new DatagramPacket(bt1, bt1.length, intaddr, n1);
  }
  catch (UnknownHostException e) {
  System.err.println(e);
  }

• Construct a in bound DatagramSocket object on the port
• Pass an empty DatagramPacket object to the DatagramSocket's receive() method.
• The calling thread will lockup until a datagram is received.
• With getPort() and and getAddress() tender the the source of packed came from,
• Use getData() to retrieve the data, and getLength() to  bytes-size were in the data.
• When received packet was too long for the buffer, the packet would truncated to the length of the buffer.
• The Length of the packet  is reset after receiving complete packet

An Example:

try {
byte buffer = new byte[45000];
DatagramPacket inDP = new DatagramPacket(buffer, buffer.length);
DatagramSocket inDS = new DatagramSocket(5678);
inDS.receive(inDP);
byte[] data = inDP.getData();
String str1 = new String(data, 0, data.getLength());
System.out.println("getPort" + inDP.getPort() + " address "
+ inDP.getAddress() + " notes:");
System.out.println(str1);
}
catch (IOException e) {
System.err.println(e);
}