Validating incoming API requests is one of the first steps to keep your Spring Boot applications safe and clean. Let's explore different approaches from simple annotations to complex custom validators.
Spring Boot integrates seamlessly with Jakarta Bean Validation (JSR-380), giving you powerful validation tools right out of the box. Whether you need basic field validation or complex business rules, there's an approach that fits your needs.
Validation in One Sentence
Spring Boot validation stops bad data at your API boundary before it reaches your business logic.
Field-Level Validation
The most straightforward approach: apply annotations directly to your fields to enforce basic constraints like required values, format validation, and numeric ranges.
And in your controller, add the @Valid
annotation to trigger validation:
Customizing Error Responses
By default, validation failures return lengthy stack traces. Clean this up with a global exception handler:
Now your API returns clean, user-friendly error messages:
Conditional Validation with @AssertTrue
Sometimes you need conditional logic: "if field A has this value, then field B must be set." Use @AssertTrue
on a custom method:
Spring calls isValidAdmin()
automatically during validation. If it returns false
, the request fails with your custom message.
Class-Level Custom Validator
For complex business rules that span multiple fields, create your own annotation and validator:
Apply the custom validator to your class:
Best Practices
-
Use field annotations for simple validation rules like
@NotBlank
,@Email
, and@Min
- Use @AssertTrue for quick conditional checks between fields
- Create custom validators for complex business rules that involve multiple fields
- Add @RestControllerAdvice to return clean, user-friendly error messages
"Good validation is like a good security guard—it stops problems at the door before they can cause damage inside."
Key Takeaways
Spring Boot's validation framework gives you multiple layers of protection. Start with simple field annotations for basic checks, then add conditional logic and custom validators as your business rules get more complex.
The key is to fail fast and fail clearly. Validate early, return meaningful error messages, and keep your business logic clean by ensuring only valid data reaches it.