java.net Package

Java provides the java.net package for developing applications that communicate over a network. The package contains classes and interfaces for working with URLs, IP addresses, sockets, and other network-related operations.

In this chapter, you will learn about the java.net package and the commonly used classes and interfaces provided for network programming in Java.

What is java.net Package?

The java.net package provides classes and interfaces for implementing network applications in Java. These classes can be used to establish network connections, communicate between applications, work with Internet addresses, and access resources through URLs.

Java programs can use the classes provided by this package to perform various network operations without directly handling the low-level details of network communication.

Classes in java.net Package

The java.net package contains several classes for performing network-related operations. Some commonly used classes are discussed below.

URL and URI Handling

The java.net package provides classes for working with URLs and URIs. A URL identifies the location of a resource, while a URI identifies a resource or provides a way to represent a resource identifier.

These classes can be used to parse network resource addresses and obtain information such as the protocol, host, port, path, and query.

Example: Using URL

In the following example, the URL class is used to obtain information about a web address.

import java.net.URL;

public class URLExample {
    public static void main(String[] args) throws Exception {
        URL url = new URL("https://www.example.com/index.html");

        System.out.println("Protocol: " + url.getProtocol());
        System.out.println("Host: " + url.getHost());
        System.out.println("Path: " + url.getPath());
    }
}

Output:

Protocol: https
Host: www.example.com
Path: /index.html

Network Communication Using Sockets

The java.net package provides Socket and ServerSocket classes for client-server communication. A server can use ServerSocket to listen for connection requests, while a client can use Socket to establish a connection with the server.

Example: Using Socket

In the following example, a Socket is created to establish a connection with a server running on the local computer.

import java.net.Socket;

public class SocketExample {
    public static void main(String[] args) {
        try {
            Socket socket = new Socket("localhost", 5000);

            System.out.println("Connection established.");

            socket.close();
        } catch (Exception e) {
            System.out.println("Unable to connect to the server.");
        }
    }
}

Output:

Unable to connect to the server.

Working with IP Addresses

The InetAddress class can be used to obtain information about Internet addresses. It can resolve a host name to an IP address and can also provide the host name associated with an address.

Example: Using InetAddress

In the following example, the InetAddress class is used to obtain the host name and IP address of the local computer.

import java.net.InetAddress;

public class InetAddressExample {
    public static void main(String[] args) throws Exception {
        InetAddress address = InetAddress.getLocalHost();

        System.out.println("Host Name: " + address.getHostName());
        System.out.println("IP Address: " + address.getHostAddress());
    }
}

Output:

Host Name: MyComputer
IP Address: 192.168.1.5

The host name and IP address in the output depend on the computer and network configuration.