Spring Boot Validation Explained with Practical Examples

Spring Boot validation explained with DTOs, Bean Validation annotations, @Valid, custom messages, nested objects, and practical API examples.

By Anderson Alvarez Vásquez · 2026-07-16

• technology
• programming
• tutorials
• Java

Spring Boot Validation Best Practices: A Practical Guide for Backend APIs Validation is a key part of building reliable Spring Boot APIs. Before data reaches the service layer, the application should verify that the request payload is complete, correctly formatted, and safe to process. Spring Boot integrates with Bean Validation, making it easy to validate DTOs using annotations such as @NotBlank , @Email , @Size , and @Valid . Why Validation Matters Validation protects your application from bad input, including: - Missing required fields - Invalid email addresses - Short passwords - Negative numbers - Invalid nested objects - Malformed request payloads Without validation, invalid data can reach the database or business logic. Use DTOs for Request Validation Avoid validating entities directly. Use request DTOs instead. java public record CreateUserRequest @NotBlank message = "Name is required" String name, @NotBlank message = "Email is required" @Email message = "Email must be valid" String email, @NotBlank message = "Password is required" @Size min = 8, message = "Password must have at least 8 characters" String password { } DTOs keep API validation separate from persistence models. Enable Validation with @Valid Use @Valid in the controller method. java @RestController @RequestMapping "/api/users" public class UserController { @PostMapping @ResponseStatus HttpStatus.CREATED public UserResponse create @Valid @RequestBody CreateUserRequest request { return userService.create request ; } } When the request is invalid, Spring Boot throws a validation exception before calling the service. Example Invalid Request json { "name": "", "email": "invalid-email", "password": "123" } This request should fail because: - name is blank. - email is not valid. - password is too...