DTO validation in Spring Boot - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a DTO in Spring Boot?

DTO stands for Data Transfer Object. It is a simple object used to carry data between processes, often between client and server, without any business logic.

beginner

Why do we validate DTOs in Spring Boot?

We validate DTOs to ensure the data received from users or clients is correct and safe before processing it. This helps prevent errors and security issues.

beginner

Which annotation is used to trigger validation on a DTO in a Spring Boot controller?

The @Valid annotation is used on a DTO parameter in a controller method to trigger validation based on the constraints defined in the DTO class.

intermediate

Name three common validation annotations used in Spring Boot DTOs.

Common annotations include @NotNull (value must not be null), @Size (limits string or collection size), and @Email (checks for valid email format).

intermediate

How does Spring Boot handle validation errors in a REST API?

Spring Boot automatically returns a 400 Bad Request response with details about which fields failed validation when a DTO annotated with @Valid fails validation.

Which annotation do you use to validate a DTO parameter in a Spring Boot controller?

A @Valid

B @Autowired

C @RequestMapping

D @Service

The @Valid annotation triggers validation on the DTO based on its constraints.

What does the @NotNull annotation ensure in a DTO field?

A Field must not be null

B Field must be a number

C Field must be unique

D Field must be a valid email

@NotNull ensures the field is not null when validated.

If a DTO validation fails in Spring Boot, what HTTP status code is typically returned?

A 200 OK

B 400 Bad Request

C 404 Not Found

D 500 Internal Server Error

Validation failures return 400 Bad Request with error details.

Which annotation checks that a string field contains a valid email format?

A @Pattern

B @Size

C @Email

D @NotBlank

@Email validates that the string is a valid email address.

Where do you place validation annotations like @NotNull or @Size in a Spring Boot project?

A On repository interfaces

B On controller methods

C On service classes

D On DTO class fields

Validation annotations are placed on DTO fields to define rules for input data.

Explain how DTO validation works in a Spring Boot REST controller from receiving data to handling errors.

Think about the flow from client input to server response.

List and describe three common validation annotations used in Spring Boot DTOs and what they check.

Focus on annotations that check presence, size, and format.