Hello! In this lecture, we will learn how to develop a basic backend application using Spring Boot. In particular, we will delve into implementing login and logout functionalities, user registration functionality using Spring Security, and enhancing the user experience through view controllers.

1. Introduction to Spring Boot and Security

Spring Boot is an application development tool based on the Spring Framework, designed to help you build applications quickly without complex configurations. Spring Security is a powerful tool for managing the security of applications and makes it easy to handle authentication and authorization.

1.1. Requirements

JDK 8 or higher
IDE (IntelliJ IDEA, Eclipse, etc.)
Maven or Gradle

1.2. Project Setup

To create a Spring Boot project, use Spring Initializr. Please add the following dependencies:

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-security</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
            <scope>runtime</scope>
        </dependency>

2. Implementing User Registration Functionality

To register a user, follow these steps:

2.1. Creating an Entity

Create a User entity to hold user information.

    @Entity
    public class User {
        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        private Long id;

        private String username;
        private String password;
        private String email;

        // Getters and Setters
    }

2.2. Creating a Repository Interface

Create a UserRepository to interact with the database using JPA.

    public interface UserRepository extends JpaRepository<User, Long> {
        Optional<User> findByUsername(String username);
    }

2.3. Writing a Service Class

Create a UserService class to handle registration logic.

    @Service
    public class UserService {
        @Autowired
        private UserRepository userRepository;

        public User registerNewUser(User user) {
            // Additional business logic (e.g., password encryption)
            return userRepository.save(user);
        }
    }

2.4. Creating a Controller

Create a UserController that provides a REST API for user registration.

    @RestController
    @RequestMapping("/api/users")
    public class UserController {
        @Autowired
        private UserService userService;

        @PostMapping("/register")
        public ResponseEntity<User> registerUser(@RequestBody User user) {
            User newUser = userService.registerNewUser(user);
            return ResponseEntity.ok(newUser);
        }
    }

2.5. Password Encryption

We will use bcrypt hash function to securely store passwords. The password will be encrypted in UserService.

    @Autowired
    private PasswordEncoder passwordEncoder;

    public User registerNewUser(User user) {
        user.setPassword(passwordEncoder.encode(user.getPassword()));
        return userRepository.save(user);
    }

3. Implementing Login and Logout Functionality

Now that user registration is complete, we will implement the login and logout functionalities.

3.1. Spring Security Configuration

Set up Spring Security to implement basic user authentication. Write the SecurityConfig class.

    @Configuration
    @EnableWebSecurity
    public class SecurityConfig extends WebSecurityConfigurerAdapter {
        @Autowired
        private UserDetailsService userDetailsService;

        @Override
        protected void configure(AuthenticationManagerBuilder auth) throws Exception {
            auth.userDetailsService(userDetailsService).passwordEncoder(passwordEncoder());
        }

        @Override
        protected void configure(HttpSecurity http) throws Exception {
            http.csrf().disable()
                .authorizeRequests()
                .antMatchers("/api/users/register").permitAll()
                .anyRequest().authenticated()
                .and()
                .formLogin()
                .loginPage("/login")
                .permitAll()
                .and()
                .logout()
                .permitAll();
        }

        @Bean
        public PasswordEncoder passwordEncoder() {
            return new BCryptPasswordEncoder();
        }
    }

3.2. Creating Login Page and Logout Functionality

Create a login page and implement logout functionality. The login page is written in HTML.

    <form action="/login" method="post">
        <label>Username:</label>
        <input type="text" name="username" required>
        <label>Password:</label>
        <input type="password" name="password" required>
        <button type="submit">Login</button>
    </form>

4. Implementing View Controller

Finally, we will create a view controller to add functionality for displaying data to the user.

4.1. Creating a Controller

Create a controller that returns HTML pages using Spring MVC’s view controllers.

    @Controller
    public class ViewController {
        @GetMapping("/register")
        public String registerForm(Model model) {
            model.addAttribute("user", new User());
            return "register";
        }

        @GetMapping("/login")
        public String loginForm() {
            return "login";
        }
    }

4.2. Using Thymeleaf Templates

Use Thymeleaf to render HTML in the view layer. Add a register.html file to the resources/templates folder.

    <html xmlns:th="http://www.w3.org/1999/xhtml">
    <body>
        <form action="@{/api/users/register}" th:object="${user}" method="post">
            <label>Username:</label>
            <input type="text" th:field="*{username}" required>
            <label>Password:</label>
            <input type="password" th:field="*{password}" required>
            <button type="submit">Register</button>
        </form>
    </body>

5. Conclusion

You have now learned how to build a simple backend application with user registration, login, and logout functionality using Spring Boot. This serves as a foundation for developing more complex applications using Spring Boot. Next steps may include database integration, API documentation, and frontend integration. If you have any questions or need further assistance, please leave a comment!

Spring Boot Backend Development Course, Implementing Login and Logout with Spring Security, Implementing Signup, Implementing View Controller