Request validation preview in Spring Boot - Mini Project: Build & Apply

Request Validation Preview in Spring Boot

📖 Scenario: You are building a simple Spring Boot web application that accepts user data through a form. To keep the data clean and safe, you want to check the user's input before saving it.

🎯 Goal: Create a Spring Boot controller that validates a user registration request using annotations. You will define a data class with validation rules, configure a controller to accept the data, and ensure validation errors are handled properly.

📋 What You'll Learn

Create a User class with fields name and email.

Add validation annotations to name and email fields.

Create a controller method to accept a POST request with a @Valid User object.

Add a BindingResult parameter to check for validation errors.

Return a simple success or error message based on validation.

💡 Why This Matters

🌍 Real World

Validating user input is essential in web applications to prevent bad data and security issues.

💼 Career

Understanding request validation is a key skill for backend developers working with Spring Boot.

1

Create User class with fields

Create a class called User with two private fields: String name and String email. Add public getters and setters for both fields.

Spring Boot

public class User {
    // Your code here
}

Need a hint?

Define private fields and generate public getter and setter methods for each.

2

Add validation annotations to User fields

Add the @NotBlank annotation to the name field and the @Email annotation to the email field in the User class. Also add @NotBlank to email to ensure it is not empty.

Spring Boot

import jakarta.validation.constraints.Email;
import jakarta.validation.constraints.NotBlank;

public class User {
    // Add validation annotations here
    private String name;
    private String email;

    // getters and setters
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }
}

Need a hint?

Use @NotBlank to ensure fields are not empty and @Email to check email format.

3

Create controller method to accept and validate User

Create a Spring Boot controller class called UserController. Inside it, write a method registerUser that handles POST requests at /register. The method should accept a @Valid User user parameter and a BindingResult bindingResult parameter. The method should return a String.

Spring Boot

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import jakarta.validation.Valid;
import org.springframework.validation.BindingResult;

@Controller
@RequestMapping("/user")
public class UserController {
    // Your code here
}

Need a hint?

Create a controller with a POST method that accepts a validated User and BindingResult.

4

Add validation check and return response

Inside the registerUser method, check if bindingResult.hasErrors() is true. If yes, return the string "Error: Invalid data". Otherwise, return "Success: User registered".

Spring Boot

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import jakarta.validation.Valid;
import org.springframework.validation.BindingResult;

@Controller
@RequestMapping("/user")
public class UserController {
    @PostMapping("/register")
    @ResponseBody
    public String registerUser(@Valid User user, BindingResult bindingResult) {
        // Your code here
    }
}

Need a hint?

Use bindingResult.hasErrors() to check validation and return messages accordingly.