Spring Framework

Table of Contents

Introduction

Spring Framework is a comprehensive framework for building enterprise Java applications. It provides infrastructure support for developing Java applications with features like dependency injection, aspect-oriented programming, and Spring Boot for rapid application development.

Key Features:

Core Features

Configuration


// Java-based configuration
@Configuration
public class AppConfig {
    @Bean
    public UserService userService() {
        return new UserServiceImpl();
    }

    @Bean
    public DataSource dataSource() {
        return new EmbeddedDatabaseBuilder()
            .setType(EmbeddedDatabaseType.H2)
            .build();
    }
}

// XML configuration
<beans>
    <bean id="userService" class="com.example.UserServiceImpl"/>
    <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource">
        <property name="driverClassName" value="com.mysql.jdbc.Driver"/>
        <property name="url" value="jdbc:mysql://localhost:3306/db"/>
    </bean>
</beans>

Dependency Injection

Constructor Injection:


@Service
public class UserServiceImpl implements UserService {
    private final UserRepository userRepository;
    private final EmailService emailService;

    @Autowired
    public UserServiceImpl(UserRepository userRepository, 
                         EmailService emailService) {
        this.userRepository = userRepository;
        this.emailService = emailService;
    }
}

Field and Setter Injection


@Service
public class ProductService {
    // Field injection
    @Autowired
    private ProductRepository productRepository;

    // Setter injection
    private PriceService priceService;

    @Autowired
    public void setPriceService(PriceService priceService) {
        this.priceService = priceService;
    }
}

Spring Boot

Basic Application:


@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}

// application.properties
spring.datasource.url=jdbc:mysql://localhost:3306/mydb
spring.jpa.hibernate.ddl-auto=update
server.port=8080

Spring Web MVC

REST Controllers


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

    @Autowired
    public UserController(UserService userService) {
        this.userService = userService;
    }

    @GetMapping
    public List<User> getAllUsers() {
        return userService.findAll();
    }

    @PostMapping
    public User createUser(@RequestBody User user) {
        return userService.save(user);
    }

    @GetMapping("/{id}")
    public User getUser(@PathVariable Long id) {
        return userService.findById(id)
            .orElseThrow(() -> new ResourceNotFoundException("User not found"));
    }
}

Spring Data

JPA Repository:


@Repository
public interface UserRepository extends JpaRepository<User, Long> {
    List<User> findByEmail(String email);
    
    @Query("SELECT u FROM User u WHERE u.status = ?1")
    List<User> findByStatus(String status);
    
    @Modifying
    @Query("UPDATE User u SET u.status = ?2 WHERE u.id = ?1")
    int updateUserStatus(Long id, String status);
}

Spring Security


@Configuration
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {
    
    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
            .authorizeRequests()
                .antMatchers("/public/**").permitAll()
                .antMatchers("/api/**").authenticated()
                .antMatchers("/admin/**").hasRole("ADMIN")
            .and()
            .formLogin()
                .loginPage("/login")
                .permitAll()
            .and()
            .logout()
                .logoutUrl("/logout")
                .permitAll();
    }
    
    @Bean
    public PasswordEncoder passwordEncoder() {
        return new BCryptPasswordEncoder();
    }
}

Best Practices

Development Guidelines:

Exception Handling


@ControllerAdvice
public class GlobalExceptionHandler {
    
    @ExceptionHandler(ResourceNotFoundException.class)
    public ResponseEntity<?> handleResourceNotFound(
            ResourceNotFoundException ex, WebRequest request) {
        ErrorDetails errorDetails = new ErrorDetails(
            new Date(), 
            ex.getMessage(), 
            request.getDescription(false));
        return new ResponseEntity<>(
            errorDetails, HttpStatus.NOT_FOUND);
    }
    
    @ExceptionHandler(Exception.class)
    public ResponseEntity<?> handleGlobalException(
            Exception ex, WebRequest request) {
        ErrorDetails errorDetails = new ErrorDetails(
            new Date(), 
            ex.getMessage(), 
            request.getDescription(false));
        return new ResponseEntity<>(
            errorDetails, HttpStatus.INTERNAL_SERVER_ERROR);
    }
}

Related Resources