UserDetailsService implementation in Spring Boot - Mini Project: Build & Apply

UserDetailsService Implementation in Spring Boot

📖 Scenario: You are building a simple Spring Boot application that needs to authenticate users. To do this, you will implement the UserDetailsService interface, which loads user data for authentication.

🎯 Goal: Create a class that implements UserDetailsService to load user details from a predefined list of users.

📋 What You'll Learn

Create a list of users with username and password

Define a variable for the default user role

Implement the loadUserByUsername method to find a user by username

Return a UserDetails object with username, password, and roles

💡 Why This Matters

🌍 Real World

UserDetailsService is used in Spring Boot applications to load user information for authentication and authorization.

💼 Career

Understanding UserDetailsService is essential for backend developers working with Spring Security to implement custom authentication logic.

1

Create a list of users

Create a private final list called users of type UserDetails with two users: username alice with password password1, and username bob with password password2. Use User.withUsername(...).password(...).roles(...).build() to create each user with role USER.

Spring Boot

import org.springframework.security.core.userdetails.User;
import org.springframework.security.core.userdetails.UserDetails;
import java.util.List;

public class MyUserDetailsService implements org.springframework.security.core.userdetails.UserDetailsService {
    // Create a private final List called users with alice and bob
    // Your code here
}

Need a hint?

Use List.of(...) to create an immutable list of UserDetails objects.

2

Add a role variable

Add a private final string variable called defaultRole and set it to USER.

Spring Boot

import org.springframework.security.core.userdetails.User;
import org.springframework.security.core.userdetails.UserDetails;
import java.util.List;

public class MyUserDetailsService implements org.springframework.security.core.userdetails.UserDetailsService {
    private final List users = List.of(
        User.withUsername("alice").password("password1").roles("USER").build(),
        User.withUsername("bob").password("password2").roles("USER").build()
    );
    // Add private final String defaultRole = "USER";
    // Your code here
}

Need a hint?

This variable will hold the role name for users.

3

Implement loadUserByUsername method

Override the loadUserByUsername method with parameter username of type String. Use a for loop with variable user to iterate over users. If user.getUsername().equals(username), return user. If no user is found, throw new UsernameNotFoundException("User not found").

Spring Boot

import org.springframework.security.core.userdetails.User;
import org.springframework.security.core.userdetails.UserDetails;
import org.springframework.security.core.userdetails.UsernameNotFoundException;
import java.util.List;

public class MyUserDetailsService implements org.springframework.security.core.userdetails.UserDetailsService {
    private final List users = List.of(
        User.withUsername("alice").password("password1").roles("USER").build(),
        User.withUsername("bob").password("password2").roles("USER").build()
    );
    private final String defaultRole = "USER";

    @Override
    public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {
        // Your code here
    }
}

Need a hint?

Use a simple for loop to find the user by username and throw an exception if not found.

4

Complete the UserDetailsService class

Add the class declaration to implement UserDetailsService interface and import UsernameNotFoundException. Ensure the class is public and named MyUserDetailsService.

Spring Boot

// Ensure the class declaration and imports are correct
// Your code here

Need a hint?

Make sure the class implements UserDetailsService and imports are complete.