@NotNull, @NotBlank, @NotEmpty in Spring Boot - Mini Project: Build & Apply

Using @NotNull, @NotBlank, and @NotEmpty in Spring Boot Validation

📖 Scenario: You are building a simple Spring Boot application to register users. You want to make sure the user data is valid before saving it.

🎯 Goal: Learn how to use the validation annotations @NotNull, @NotBlank, and @NotEmpty on a user data class to enforce input rules.

📋 What You'll Learn

Create a User class with fields for name, email, and roles

Use @NotNull on the roles list to ensure it is not null

Use @NotBlank on the email field to ensure it is not empty or just spaces

Use @NotEmpty on the name field to ensure it is not empty

Add the necessary imports for validation annotations

💡 Why This Matters

🌍 Real World

Validating user input in web applications to prevent bad or missing data before saving to a database.

💼 Career

Understanding and applying validation annotations is essential for backend developers working with Spring Boot to build reliable APIs.

1

Create the User class with fields

Create a public class called User with three fields: String name, String email, and List<String> roles. Do not add any annotations yet.

Spring Boot

public class User {
    // Your code here
}

Need a hint?

Think of User as a box holding name, email, and roles information.

2

Add validation imports

Add import statements for javax.validation.constraints.NotNull, javax.validation.constraints.NotBlank, and javax.validation.constraints.NotEmpty at the top of the User class file.

Spring Boot

// Add the three import statements here
import java.util.List;

public class User {
    String name;
    String email;
    List roles;
}

Need a hint?

These imports bring in the validation rules you will use on the fields.

3

Add validation annotations to fields

Add @NotEmpty above the name field, @NotBlank above the email field, and @NotNull above the roles field in the User class.

Spring Boot

import java.util.List;
import javax.validation.constraints.NotNull;
import javax.validation.constraints.NotBlank;
import javax.validation.constraints.NotEmpty;

public class User {
    // Add @NotEmpty here
    String name;
    // Add @NotBlank here
    String email;
    // Add @NotNull here
    List roles;
}

Need a hint?

Each annotation enforces a different rule: @NotEmpty means the name cannot be empty, @NotBlank means email cannot be blank or spaces, and @NotNull means roles list cannot be null.

4

Complete the User class with public access and add getters

Make the User class public and add public getter methods for name, email, and roles fields.

Spring Boot

import java.util.List;
import javax.validation.constraints.NotNull;
import javax.validation.constraints.NotBlank;
import javax.validation.constraints.NotEmpty;

// Make class public and add getters
public class User {
    @NotEmpty
    String name;

    @NotBlank
    String email;

    @NotNull
    List roles;

    // Your code here
}

Need a hint?

Getters allow other parts of the program to read the field values safely.