Domain Label (Single Segment) Regex for Java

What this pattern does

This page provides a well-structured, multi-part regular expression for matching domain label (single segment), 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

// Domain Label (Single Segment)
// ReDoS-safe | RegexVault — Web & Network > Domain

import java.util.regex.Pattern;

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

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

    // Example
    public static void main(String[] args) {
        System.out.println(validate("example")); // 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 63-character maximum is per RFC 1034. The last invalid test case is 64 chars (one over the limit). Use for validating individual hostname components.