Java DatagramSocket and DatagramPacket: UDP Connection-Less Socket Programming

Explore the DatagramSocket and DatagramPacket classes in Java, essential for connection-less socket programming using the UDP protocol. Learn how datagrams facilitate data transmission across networks without guaranteed delivery, offering a lightweight alternative to TCP in Java networking.

Java DatagramSocket and DatagramPacket

The Java DatagramSocket and DatagramPacket classes are used for connection-less socket programming using UDP instead of TCP.

Datagram

Datagrams are collections of information sent from one device to another via a network. There is no assurance that the datagram will reach the target device safely or completely. UDP protocol implements datagrams in Java.

Java DatagramSocket Class

Java DatagramSocket class represents a connection-less socket for sending and receiving datagram packets.

Commonly used constructors:

  • DatagramSocket() throws SocketException: Creates a datagram socket and binds it with the available Port Number on the localhost machine.
  • DatagramSocket(int port) throws SocketException: Creates a datagram socket and binds it with the given Port Number.
  • DatagramSocket(int port, InetAddress address) throws SocketException: Creates a datagram socket and binds it with the specified port number and host address.

Java DatagramSocket Class Methods

Method Description
void bind(SocketAddress addr) Binds the DatagramSocket to a specific address and port.
void close() Closes the datagram socket.
void connect(InetAddress address, int port) Connects the socket to a remote address.
void disconnect() Disconnects the socket.
boolean getBroadcast() Tests if SO_BROADCAST is enabled.
DatagramChannel getChannel() Returns the unique DatagramChannel object associated with the socket.
InetAddress getInetAddress() Returns the address to which the socket is connected.
InetAddress getLocalAddress() Gets the local address to which the socket is connected.
int getLocalPort() Returns the port number on the local host to which the socket is bound.
SocketAddress getLocalSocketAddress() Returns the address of the endpoint the socket is bound to.
int getPort() Returns the port number to which the socket is connected.
int getReceiverBufferSize() Gets the value of the SO_RCVBUF option for this DatagramSocket.
boolean isClosed() Returns the status of the socket.
boolean isConnected() Returns the connection state of the socket.
void send(DatagramPacket p) Sends the datagram packet from the socket.
void receive(DatagramPacket p) Receives the datagram packet from the socket.

Java DatagramPacket Class

Java DatagramPacket is a message that can be sent or received. It is a data container, and if multiple packets are sent, they may arrive in any order. Packet delivery is not guaranteed.

Commonly used constructors:

  • DatagramPacket(byte[] barr, int length): Creates a datagram packet for receiving packets.
  • DatagramPacket(byte[] barr, int length, InetAddress address, int port): Creates a datagram packet for sending packets.

Java DatagramPacket Class Methods

Method Description
InetAddress getAddress() Returns the IP address of the machine to which the datagram is being sent or from which it was received.
byte[] getData() Returns the data buffer.
int getLength() Returns the length of the data to be sent or received.
int getOffset() Returns the offset of the data to be sent or received.
int getPort() Returns the port number on the remote host to which the datagram is being sent or from which it was received.
SocketAddress getSocketAddress() Gets the SocketAddress (IP address + port number) of the remote host.
void setAddress(InetAddress iaddr) Sets the IP address of the machine to which the datagram is being sent.
void setData(byte[] buff) Sets the data buffer for the packet.
void setLength(int length) Sets the length of the packet.
void setPort(int iport) Sets the port number on the remote host to which the datagram is being sent.
void setSocketAddress(SocketAddress addr) Sets the SocketAddress (IP address + port number) of the remote host.

Example of Sending DatagramPacket by DatagramSocket

Syntax

import java.net.*;

public class DSender {
public static void main(String[] args) throws Exception {
    DatagramSocket ds = new DatagramSocket();
    String str = "Welcome java";
    InetAddress ip = InetAddress.getByName("127.0.0.1");

    DatagramPacket dp = new DatagramPacket(str.getBytes(), str.length(), ip, 3000);
    ds.send(dp);
    ds.close();
}
}
Output

DatagramSocket and DatagramPacket

Example of Receiving DatagramPacket by DatagramSocket

Syntax

import java.net.*;

public class DReceiver {
public static void main(String[] args) throws Exception {
    DatagramSocket ds = new DatagramSocket(3000);
    byte[] buf = new byte[1024];
    DatagramPacket dp = new DatagramPacket(buf, 1024);
    ds.receive(dp);
    String str = new String(dp.getData(), 0, dp.getLength());
    System.out.println(str);
    ds.close();
}
}
Output

Welcome java