What is a GUID in Java?

A GUID (or UUID) is a 128-bit number used to uniquely identify data in systems. It is typically formatted as:

xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx

Where:

• x is a hexadecimal digit

• M indicates the version

• N indicates the variant

  
  

A GUID helps ensure global uniqueness in distributed systems, databases, or API transactions.

Java Regex Pattern for GUID

The commonly used regex pattern for validating GUIDs:

^[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}$

What it matches:

• 8 hexadecimal digits

• A hyphen

• 4 hexadecimal digits

• A hyphen

• 4 hexadecimal digits starting with version 1–5

• A hyphen

• 4 hexadecimal digits starting with 8, 9, A, or B (variant)

• A hyphen

• 12 hexadecimal digits

Online UUID / GUID Validation

If you’re looking to validate a GUID or UUID quickly without diving into code, several online tools are available for instant checking. Simply paste your value into a validator, and it will confirm if it matches the expected structure. This is especially handy when you want to double-check sample data, API responses, or generated keys on the fly.

Java Code Example

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

public class GUIDValidator {
    public static void main(String[] args) {
        String input = "3f2504e0-4f89-11d3-9a0c-0305e82c3301";

        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(input);

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

Sample Inputs

Valid GUIDs:

• 3f2504e0-4f89-11d3-9a0c-0305e82c3301

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

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

Invalid GUIDs:

• 3f2504e0-4f89-11d3-9a0c0305e82c3301 (missing hyphen)

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

• 12345 (too short)

Pro Tips

• Always validate GUIDs before storing or using them in APIs or sessions.

• GUIDs are case-insensitive. Your regex should allow both uppercase and lowercase letters (use ).

• Remove whitespace or invisible characters before running regex checks.

• If you’re generating GUIDs in Java, use for guaranteed format compliance.

• For stricter validation, create version-specific patterns (e.g., only v4 UUIDs).

• Never expose internal or sensitive GUIDs directly—hash or encode them with a hash generator or a Base64 Encoder.

  
  

  Why?

  
  Directly exposing GUIDs in URLs, logs, or API responses can inadvertently leak system structure, user IDs, or sensitive references. To avoid this, always sanitize or mask GUIDs before external use. Hashing or encoding is a simple way to add an extra layer of security, helping you protect everything from user sessions to resource identifiers.

  
  

  Pro Security Tip:

  • When integrating with client-side code, never trust incoming GUIDs—validate first, then sanitize or encode before any onward processing.

  • For tasks like converting GUIDs to different formats (hex, base64, string), or validating them across various languages (Java, C#, JavaScript, Go), make use of trusted online validators and converters.

  • For bulk operations (CSV, Excel), always validate GUID columns before import, and consider encoding before sharing files externally.

Use Cases

• API Key Validation: Ensure passed tokens follow GUID structure.

• Database Keys: Confirm format of primary or foreign keys.

• Logging Systems: Clean and validate UUID-based log identifiers.

• Form Submissions: Accept only properly formatted GUIDs in front-end fields.

  
  

Combine with These Tools

• UUID Regex Java Validator: Verify general UUIDs with version-specific matching.

• Java Regex Tester: Tweak and test regex variations for different formats.

• Token Generator: Generate unique tokens that mimic GUID formats.

• Base64 Encoder: Encode validated GUIDs for secure transmission or storage.

  
  

Related Validator Tools

Working with GUIDs or other formats in your application often means validating more than just one field. Here are some handy online validator and tester tools you might find useful as you work with regular expressions or structured data:

• Regex Tester – Instantly verify and debug your regular expressions.

• CSS Validator – Check your CSS code for errors and best practices.

• JavaScript Validator – Ensure your JS code is error-free.

• JavaScript Tester – Run and test JavaScript code snippets on the fly.

• HTML Tester – Try out and validate your HTML code quickly.

• JSON Validator – Validate JSON data for correct syntax and structure.

• XML Validator – Check XML files for well-formedness and validity.

• YAML Validator – Validate YAML files to avoid formatting issues.

• UUID / GUID Validator – Specifically check and test GUID/UUID formats.

  
  

These tools streamline the process of catching errors early, whether you're dealing with styling, data interchange formats, or code logic. Many are free and available online, making them accessible for all stages of your development workflow.

Whether you’re writing your own validator in Java or leveraging an online tool, ensuring GUIDs and UUIDs are properly formatted is a foundational step for robust, secure systems.