How to Verify if an IP Address Falls Within a Given Range in Java

How can I determine if a given IP address is within a specified range using Java?

In Java, determining whether an IP address falls within a specified range involves converting the IP addresses to their numeric representations and checking if the given IP address is within the boundaries defined by the range.

import java.net.InetAddress;
import java.net.UnknownHostException;

public class IPRangeChecker {
    public static void main(String[] args) throws UnknownHostException {
        String startIP = "192.168.1.1";
        String endIP = "192.168.1.255";
        String checkIP = "192.168.1.50";

        boolean isInRange = isInRange(startIP, endIP, checkIP);
        System.out.println("Is IP in range? " + isInRange);
    }

    public static boolean isInRange(String startIP, String endIP, String checkIP) throws UnknownHostException {
        long start = ipToLong(startIP);
        long end = ipToLong(endIP);
        long check = ipToLong(checkIP);
        return check >= start && check <= end;
    }

    private static long ipToLong(String ip) throws UnknownHostException {
        InetAddress address = InetAddress.getByName(ip);
        byte[] bytes = address.getAddress();
        long result = 0;
        for (byte b : bytes) {
            result = (result << 8) | (b & 0xFF);
        }
        return result;
    }
}

Causes

• Misinterpretation of IP address formats (IPv4 vs. IPv6)
• Improper conversion of IP addresses to their numeric forms
• Incorrectly defined range boundaries (start and end IP addresses)

Solutions

• Use the `InetAddress` class for proper handling of IP addresses.
• Convert IP addresses into their long numeric format for easy comparison.
• Implement proper error handling to catch invalid IP addresses.

Mistake: Using incorrect formats for IP addresses (e.g., using IPv6 when the range is defined for IPv4).

Solution: Ensure consistency in IP address formats across the application.

Mistake: Neglecting to handle exceptions when converting IP addresses.

Solution: Implement proper try-catch blocks to handle `UnknownHostException`.

Mistake: Not considering the edge cases for IP address comparison (e.g., start IP equals end IP).

Solution: Add checks to handle these specific scenarios.