How to Create Custom Bean Validation in Spring Boot

Learn how to define and apply custom bean validation in Spring Boot using custom annotations and ConstraintValidator. Includes real-world example and best practices.

Let’s go step-by-step to understand how to define and use a custom validation annotation.

Why Custom Validation?

Spring Boot supports many built-in validations (like @NotBlank, @Email, etc.).
But if you have business-specific rules, like:

• Username must start with “USR”
• Age must be a prime number
• ZIP code must match a certain region

➡️ You’ll need a custom validator.

🛠️ Step-by-Step: Create a Custom Validator

Let’s create a custom annotation called @StartsWithUSR to validate usernames.

✅ Step 1: Add spring-boot-starter-validation

If you’re not already using it, add this dependency in pom.xml:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-validation</artifactId>
</dependency>

✅ Step 2: Create Custom Annotation

import jakarta.validation.Constraint;
import…