Java Networking Basics

⏱ Estimated reading time: 3 min

Java provides a rich set of API classes in the java.net package to create network-based applications. Networking allows computers to communicate and exchange data over LAN, WAN, or the Internet.

1. Key Networking Concepts

2. Java Networking Classes

• InetAddress → Represents IP addresses and hostnames

• URL & URLConnection → Access resources over HTTP, FTP, or other protocols

• Socket → Client-side communication endpoint

• ServerSocket → Server-side socket that listens for connections

3. InetAddress Example

import java.net.*;

public class InetAddressExample {
    public static void main(String[] args) throws Exception {
        InetAddress address = InetAddress.getByName("www.google.com");
        System.out.println("Host Name: " + address.getHostName());
        System.out.println("IP Address: " + address.getHostAddress());
    }
}

Output (example):

Host Name: www.google.com
IP Address: 142.250.191.4

4. URL and URLConnection Example

import java.net.*;
import java.io.*;

public class URLExample {
    public static void main(String[] args) throws Exception {
        URL url = new URL("https://www.example.com");
        BufferedReader br = new BufferedReader(new InputStreamReader(url.openStream()));
        String line;
        while((line = br.readLine()) != null) {
            System.out.println(line);
        }
        br.close();
    }
}

• Reads HTML content from a web page

• Demonstrates client-side HTTP communication

5. Socket Programming

A. Server Example

import java.net.*;
import java.io.*;

public class Server {
    public static void main(String[] args) throws Exception {
        ServerSocket server = new ServerSocket(5000);
        System.out.println("Server is listening...");
        Socket socket = server.accept();
        BufferedReader br = new BufferedReader(new InputStreamReader(socket.getInputStream()));
        String message = br.readLine();
        System.out.println("Message from client: " + message);
        br.close();
        socket.close();
        server.close();
    }
}

B. Client Example

import java.net.*;
import java.io.*;

public class Client {
    public static void main(String[] args) throws Exception {
        Socket socket = new Socket("localhost", 5000);
        PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
        out.println("Hello, Server!");
        out.close();
        socket.close();
    }
}

• Server listens on port 5000

• Client connects and sends a message

• Demonstrates TCP communication

6. Key Points

• Java networking uses TCP/IP protocols

• Socket → Client-side; ServerSocket → Server-side

• InetAddress → Handles IP addresses and hostnames

• URL & URLConnection → Access remote resources over protocols

• Supports both synchronous and asynchronous communication

7. Advantages of Java Networking

• Enables distributed applications

• Platform-independent network communication

• Simplifies HTTP, FTP, and TCP/IP programming

• Integrates easily with Java GUI, Swing, and multithreading for client-server applications

8. Conclusion

Java Networking APIs allow developers to build robust, platform-independent network applications, including web clients, chat applications, and distributed systems. Understanding sockets, URLs, and IP addressing is fundamental for modern Java programming.