Spring Framework

🌱 What is Spring Framework?

Spring Framework is a comprehensive Java platform that provides infrastructure support for developing robust applications. It simplifies enterprise Java development through dependency injection, aspect-oriented programming, and extensive integration capabilities.


// Simple Spring Bean example
@Component
public class HelloService {
    public String sayHello(String name) {
        return "Hello, " + name + "!";
    }
}

Core Spring Concepts

💉

Dependency Injection

Automatic object creation and wiring

@Autowired
private UserService userService;

🏗️

IoC Container

Manages object lifecycle and dependencies

@Configuration
@ComponentScan
public class AppConfig {}

🎯

AOP

Aspect-Oriented Programming support

@Aspect
@Component
public class LoggingAspect {}

🔧

Annotations

Configuration through annotations

@Service
@Repository
@Controller

🔹 Basic Spring Application

Here's a simple Spring application structure:

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

// Service Class
@Service
public class UserService {
    public User findUser(Long id) {
        return new User(id, "John Doe");
    }
}

// Controller Class
@RestController
public class UserController {
    
    @Autowired
    private UserService userService;
    
    @GetMapping("/user/{id}")
    public User getUser(@PathVariable Long id) {
        return userService.findUser(id);
    }
}

Output:

GET /user/1 → {"id": 1, "name": "John Doe"}

🔹 Spring Configuration

Configure Spring using Java-based configuration:

@Configuration
@EnableWebMvc
@ComponentScan(basePackages = "com.example")
public class WebConfig {
    
    @Bean
    public DataSource dataSource() {
        HikariDataSource dataSource = new HikariDataSource();
        dataSource.setJdbcUrl("jdbc:h2:mem:testdb");
        return dataSource;
    }
    
    @Bean
    public JdbcTemplate jdbcTemplate(DataSource dataSource) {
        return new JdbcTemplate(dataSource);
    }
}

🔹 Spring Annotations

Common Spring annotations for beginners:

// Component Annotations
@Component      // Generic component
@Service        // Business logic layer
@Repository     // Data access layer
@Controller     // Web layer

// Dependency Injection
@Autowired      // Inject dependencies
@Qualifier      // Specify which bean to inject
@Value          // Inject property values

// Configuration
@Configuration  // Configuration class
@Bean          // Define a bean
@ComponentScan // Scan for components