Fully Qualified Domain Name (FQDN) Regex for Java

What this pattern does

This page provides a well-structured, multi-part regular expression for matching fully qualified domain name (fqdn), ported and verified for Java. A rigorously tested regex reduces debugging time and protects your application from edge-case failures. The snippet below is ready to drop into your Java project — whether you're validating in a Spring Boot controller, a Jakarta EE service, or a standalone utility class.

Java Implementation

// Fully Qualified Domain Name (FQDN)
// ReDoS-safe | RegexVault — Web & Network > Domain

import java.util.regex.Pattern;

public class FullyQualifiedDomainNameFqdnValidator {
    private static final Pattern PATTERN =
        Pattern.compile("^(?:[a-zA-Z0-9](?:[a-zA-Z0-9\\-]{0,61}[a-zA-Z0-9])?\\.)+[a-zA-Z]{2,63}\\.$");

    public static boolean validate(String input) {
        return PATTERN.matcher(input).matches();
    }

    // Example
    public static void main(String[] args) {
        System.out.println(validate("example.com.")); // true
    }
}

Test Cases

When to use this pattern

This pattern is drawn from the Web & Network > Domain category and carries a ReDoS-safe certification. That matters for Java developers because critical in Java applications since the JVM regex engine uses backtracking and is susceptible to ReDoS without careful pattern design. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

The trailing dot is the canonical FQDN form. DNS software accepts FQDNs natively. Strip trailing dots before use in HTTP Host headers — browsers do not send the trailing dot.