Socket (TCP & UDP) communication in Java

Socket communication in Java enables communication between two endpoints over a network. There are two main types of sockets: TCP sockets and UDP sockets. Let's explain both types with examples:

TCP Socket Communication:

1. **Server Side**:

   - The server creates a `ServerSocket` object to listen for incoming connections on a specific port.

   - When a client connects, the server accepts the connection and creates a `Socket` object to communicate with the client.

   - The server reads from and writes to the socket's input and output streams to communicate with the client.

import java.io.*;

import java.net.*;

public class TCPServer {

    public static void main(String[] args) throws IOException {

        ServerSocket serverSocket = new ServerSocket(12345);

        System.out.println("Server started. Waiting for client...");

        Socket clientSocket = serverSocket.accept();

        System.out.println("Client connected.");

        BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));

        PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);

        String message = in.readLine();

        System.out.println("Client says: " + message);

        out.println("Hello from server!");

        clientSocket.close();

        serverSocket.close();

    }

}

2. Client Side:

   - The client creates a `Socket` object and connects to the server using its IP address and port number.

   - The client communicates with the server by reading from and writing to the socket's input and output streams.

import java.io.*;

import java.net.*;

public class TCPClient {

    public static void main(String[] args) throws IOException {

        Socket socket = new Socket("localhost", 12345);

        PrintWriter out = new PrintWriter(socket.getOutputStream(), true);

        BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));

        out.println("Hello from client!");

        String response = in.readLine();

        System.out.println("Server response: " + response);

        socket.close();

    }

}

UDP Socket Communication:

1. Server Side:

   - The server creates a `DatagramSocket` object to send and receive datagrams (packets) over the network.

   - The server listens for incoming datagrams on a specific port.

   - The server processes incoming datagrams and sends response datagrams if necessary.

import java.io.*;

import java.net.*;

public class UDPServer {

    public static void main(String[] args) throws IOException {

        DatagramSocket serverSocket = new DatagramSocket(12345);

        byte[] receiveData = new byte[1024];

        byte[] sendData;

        System.out.println("Server started. Waiting for client...");

        DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);

        serverSocket.receive(receivePacket);

        String message = new String(receivePacket.getData()).trim();

        System.out.println("Client says: " + message);

        InetAddress clientAddress = receivePacket.getAddress();

        int clientPort = receivePacket.getPort();

        sendData = "Hello from server!".getBytes();

        DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, clientAddress, clientPort);

        serverSocket.send(sendPacket);

        serverSocket.close();

    }

}

2. Client Side:

   - The client creates a `DatagramSocket` object to send and receive datagrams.

   - The client sends datagrams to the server's IP address and port number.

   - The client receives response datagrams from the server.

import java.io.*;

import java.net.*;

public class UDPClient {

    public static void main(String[] args) throws IOException {

        DatagramSocket clientSocket = new DatagramSocket();

        InetAddress serverAddress = InetAddress.getByName("localhost");

        int serverPort = 12345;

        byte[] sendData = "Hello from client!".getBytes();

        DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, serverAddress, serverPort);

        clientSocket.send(sendPacket);

        byte[] receiveData = new byte[1024];

        DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);

        clientSocket.receive(receivePacket);

        String response = new String(receivePacket.getData()).trim();

        System.out.println("Server response: " + response);

        clientSocket.close();

    }

}

 Conclusion:

Socket communication in Java allows for the exchange of data between two endpoints over a network. TCP sockets provide reliable, connection-oriented communication, while UDP sockets offer lightweight, connectionless communication. Understanding socket programming is essential for developing networked applications in Java.