@Valid annotation on request body in Spring Boot - Mini Project: Build & Apply

Using @Valid Annotation on Request Body in Spring Boot

📖 Scenario: You are building a simple Spring Boot REST API to register users. You want to make sure the user data sent in the request body is valid before processing it.

🎯 Goal: Learn how to use the @Valid annotation on a request body to automatically validate incoming data in a Spring Boot controller.

📋 What You'll Learn

Create a User class with validation annotations

Create a controller method that accepts a User object in the request body

Use the @Valid annotation on the request body parameter

Add a configuration to handle validation errors gracefully

💡 Why This Matters

🌍 Real World

Validating user input in REST APIs is essential to prevent bad data from entering your system and to provide clear feedback to API clients.

💼 Career

Backend developers often need to validate incoming data in web applications. Knowing how to use @Valid in Spring Boot is a common and important skill.

1

Create User class with validation annotations

Create a class called User with two fields: String name and String email. Add @NotBlank annotation on name and @Email annotation on email. Import the annotations from jakarta.validation.constraints.

Spring Boot

public class User {
    // Your code here
}

Need a hint?

Use @NotBlank on the name field and @Email on the email field inside the User class.

2

Create controller with POST method accepting User

Create a Spring REST controller class called UserController. Add a method registerUser that handles POST requests at /users. The method should accept a @RequestBody User user parameter and return String.

Spring Boot

import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class UserController {
    // Your code here
}

Need a hint?

Use @RestController on the class and @PostMapping("/users") on the method. The method should accept @RequestBody User user.

3

Add @Valid annotation to request body parameter

Modify the registerUser method to add the @Valid annotation before the @RequestBody User user parameter to enable validation.

Spring Boot

import jakarta.validation.Valid;

@RestController
public class UserController {
    @PostMapping("/users")
    public String registerUser(@Valid @RequestBody User user) {
        // Your code here
    }
}

Need a hint?

Put @Valid right before @RequestBody User user in the method parameter.

4

Add exception handler for validation errors

Add a method in UserController annotated with @ExceptionHandler(MethodArgumentNotValidException.class) that returns a String message "Validation failed" when validation errors occur.

Spring Boot

import org.springframework.web.bind.MethodArgumentNotValidException;
import org.springframework.web.bind.annotation.ExceptionHandler;

@RestController
public class UserController {
    @PostMapping("/users")
    public String registerUser(@Valid @RequestBody User user) {
        return "User registered: " + user.getName();
    }

    // Add exception handler method below
}

Need a hint?

Create a method annotated with @ExceptionHandler(MethodArgumentNotValidException.class) that returns the string "Validation failed".