DTOs & Validation
Learn how to use DTOs and apply validation rules in Spring Boot.
DTOs & Validation is a free Java Academy lesson on CoddyKit — lesson 2 of 3. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Java Academy learning path, one of 3 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Intro
DTOs (Data Transfer Objects) carry structured data across layers. They are not entities or database models.
Why DTOs
DTOs simplify APIs by exposing only needed fields, hiding database details, and improving security.
Code: DTO class
A simple DTO defines fields and getters/setters, separate from database entities.
public class UserDto {
private String name;
private int age;
// getters and setters
public String getName() { return name; }
public void setName(String name) { this.name = name; }
public int getAge() { return age; }
public void setAge(int age) { this.age = age; }
}
Validation
Validation ensures DTO data meets requirements (e.g., not empty, age positive).
Code: Validation annotations
Use annotations like @NotBlank and @Min to enforce validation rules.
import jakarta.validation.constraints.*;public class UserDto {
@NotBlank
private String name;
@Min(0)
private int age;
// getters/setters omitted for brevity
}
Code: Controller with validation
@Valid triggers validation of the DTO before method logic runs.
import org.springframework.web.bind.annotation.*;import org.springframework.validation.annotation.*;import jakarta.validation.*;@RestController
@RequestMapping("/users")
class UserController {
@PostMapping
public String create(@Valid @RequestBody UserDto dto) {
return "Received: " + dto.getName() + ", " + dto.getAge();
}
}
DTO check
Quick check: What is the purpose of a DTO in Spring Boot?
Recap
Recap: Created a DTO, added validation annotations, and used it in a controller with @Valid.
Frequently asked questions
Is the “DTOs & Validation” lesson free?
Yes — the full text of “DTOs & Validation” is free to read here on the web, and the Java Academy course includes 3 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Java Academy course, upgrade to CoddyKit PRO.
What will I learn in “DTOs & Validation”?
Learn how to use DTOs and apply validation rules in Spring Boot. You practise Java Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Java Academy?
No prior experience is required. Java Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 3, so you can start here or from the beginning and move at your own pace.
How long does the “DTOs & Validation” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Java Academy lesson?
Yes. Every Java Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Project Setup & Starters
- DTOs & Validation
- Mini Project: REST API