Java DatagramSocket and DatagramPacket

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

Datagram

Datagrams are collection of information sent from one device to another device via the established network. When the datagram is sent to the targeted device, there is no assurance that it will reach to the target device safely and completely. It may get damaged or lost in between. Likewise, the receiving device also never know if the datagram received is damaged or not. The UDP protocol is used to implement the datagrams in Java.

Java DatagramSocket class

Java DatagramSocket class represents a connection-less socket for sending and receiving datagram packets. It is a mechanism used for transmitting datagram packets over network.`

A datagram is basically an information but there is no guarantee of its content, arrival or arrival time.

Commonly used Constructors of DatagramSocket class

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

Java DatagramSocket Class

Method	Description
void bind(SocketAddress addr)	It binds the DatagramSocket to a specific address and port.
void close()	It closes the datagram socket.
void connect(InetAddress address, int port)	It connects the socket to a remote address for the socket.
void disconnect()	It disconnects the socket.
boolean getBroadcast()	It tests if SO_BROADCAST is enabled.
DatagramChannel getChannel()	It returns the unique DatagramChannel object associated with the datagram socket.
InetAddress getInetAddress()	It returns the address to where the socket is connected.
InetAddress getLocalAddress()	It gets the local address to which the socket is connected.
int getLocalPort()	It returns the port number on the local host to which the socket is bound.
SocketAddress getLocalSocketAddress()	It returns the address of the endpoint the socket is bound to.
int getPort()	It returns the port number to which the socket is connected.
int getReceiverBufferSize()	It gets the value of the SO_RCVBUF option for this DatagramSocket that is the buffer size used by the platform for input on the DatagramSocket.
boolean isClosed()	It returns the status of socket i.e. closed or not.
boolean isConnected()	It returns the connection state of the socket.
void send(DatagramPacket p)	It sends the datagram packet from the socket.
void receive(DatagramPacket p)	It 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. If you send multiple packet, it may arrive in any order. Additionally, packet delivery is not guaranteed.

Commonly used Constructors of DatagramPacket class

DatagramPacket(byte[] barr, int length): it creates a datagram packet. This constructor is used to receive the packets.
DatagramPacket(byte[] barr, int length, InetAddress address, int port): it creates a datagram packet. This constructor is used to send the packets.

Java DatagramPacket Class Methods

Method	Description
1) InetAddress getAddress()	It returns the IP address of the machine to which the datagram is being sent or from which the datagram was received.
2) byte[] getData()	It returns the data buffer.
3) int getLength()	It returns the length of the data to be sent or the length of the data received.
4) int getOffset()	It returns the offset of the data to be sent or the offset of the data received.
5) int getPort()	It returns the port number on the remote host to which the datagram is being sent or from which the datagram was received.
6) SocketAddress getSocketAddress()	It gets the SocketAddress (IP address + port number) of the remote host that the packet is being sent to or is coming from.
7) void setAddress(InetAddress iaddr)	It sets the IP address of the machine to which the datagram is being sent.
8) void setData(byte[] buff)	It sets the data buffer for the packet.
9) void setLength(int length)	It sets the length of the packet.
10) void setPort(int iport)	It sets the port number on the remote host to which the datagram is being sent.
11) void setSocketAddress(SocketAddress addr)	It sets the SocketAddress (IP address + port number) of the remote host to which the datagram is being sent.

Example of Sending DatagramPacket by DatagramSocket

//DSender.java
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:

Example of Receiving DatagramPacket by DatagramSocket

//DReceiver.java
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: