Spring Boot Validation: Guarding REST APIs Against Invalid Input

This DEV Community tutorial explains how to add input validation to Spring Boot REST APIs using the spring-boot-starter-validation dependency. It recommends placing @Valid before any @RequestBody parameter in controllers, especially for POST and PUT requests where clients send data. The article outlines standard JSR-380 constraints such as @NotBlank, @Size, @Email, and @Min, and shows how they are applied to a Task entity. When validation fails, Spring intercepts the request, throws MethodArgumentNotValidException, and returns an HTTP 400 Bad Request, with custom messages configurable inline or via messages.properties. The author suggests using DTOs in production applications to keep business logic and database layers protected.