What is a UUID?

A UUID (or GUID) is a 128-bit identifier used to uniquely label data. It appears as a 36-character string in this format:

xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx

• M: Indicates UUID version (1–5)

• N: Indicates the variant (typically 8, 9, A, or B in hex)

UUIDs are essential for unique identification across APIs, distributed systems, databases, and resource tagging.

Java Regex Pattern for UUID

To match standard UUIDs (versions 1–5):

"^[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[1-5][0-9a-fA-F]{3}-[89abAB][0-9a-fA-F]{3}-[0-9a-fA-F]{12}$"

Pattern Breakdown:

• [0-9a-fA-F]{8} – First group (8 hex digits)

• [0-9a-fA-F]{4} – Second group (4 hex digits)

• [1-5][0-9a-fA-F]{3} – Version (1–5)

• [89abAB][0-9a-fA-F]{3} – Variant

• [0-9a-fA-F]{12} – Final group (12 hex digits)

To strictly validate version 4 UUIDs:

"[a-fA-F0-9]{8}-[a-fA-F0-9]{4}-4[a-fA-F0-9]{3}-[89abAB][a-fA-F0-9]{3}-[a-fA-F0-9]{12}"

Java Code Example

import java.util.regex.Pattern;
import java.util.regex.Matcher;

public class UUIDValidator {
    public static void main(String[] args) {
        String uuid = "550e8400-e29b-41d4-a716-446655440000";
        String regex = "^[0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[1-5][0-9a-fA-F]{3}-[89abAB][0-9a-fA-F]{3}-[0-9a-fA-F]{12}$";
        
        Pattern pattern = Pattern.compile(regex);
        Matcher matcher = pattern.matcher(uuid);

        if (matcher.matches()) {
            System.out.println("Valid UUID");
        } else {
            System.out.println("Invalid UUID");
        }
    }
}

Reusable Java UUID Patterns

// Generic UUID (any version)
public static final String UUID_STRING = "[a-fA-F0-9]{8}-[a-fA-F0-9]{4}-[a-fA-F0-9]{4}-[a-fA-F0-9]{4}-[a-fA-F0-9]{12}";
public static final Pattern UUID = Pattern.compile(UUID_STRING, Pattern.CASE_INSENSITIVE);

// Version 4 UUID only
public static final String UUID_V4_STRING = "[a-fA-F0-9]{8}-[a-fA-F0-9]{4}-4[a-fA-F0-9]{3}-[89abAB][a-fA-F0-9]{3}-[a-fA-F0-9]{12}";
public static final Pattern UUID_V4 = Pattern.compile(UUID_V4_STRING, Pattern.CASE_INSENSITIVE);

Valid UUID Examples

• 123e4567-e89b-12d3-a456-426614174000

• 550e8400-e29b-41d4-a716-446655440000

Invalid UUID Examples

• 123e4567e89b12d3a456426614174000 (missing hyphens)

• zzzzzzzz-zzzz-zzzz-zzzz-zzzzzzzzzzzz (non-hex characters)

• 123e4567-e89b-62d3-a456-426614174000 (invalid version)

Common Use Cases

• Database Keys – Use UUIDs as non-sequential primary keys

• Microservices – Avoid key collisions in distributed systems

• API Resources – Identify RESTful endpoints and resources

• User IDs – Generate anonymous, secure user identifiers

Pro Tips

• Use version 4 UUIDs for better randomness

• Always validate UUIDs on both frontend and backend

• Normalize UUIDs by storing them in lowercase

• Store UUIDs as VARCHAR(36) in SQL to retain format

• Regex only checks format—use libraries for actual UUID generation

Related Tools to Combine With

• Java Regex Tester – Modify and test UUID regex variations

• Token Generator – Generate secure alphanumeric tokens

• Base64 Encoder – Encode UUIDs for transmission

• UUID Generator – Instantly create UUIDs for tests

• Email Regex Java Validator – Validate email formats

• Password Regex Java Validator – Test strong password patterns