Spring Annotations

@Component
class MyClass {}

@Autowired
private MyClass obj;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import org.springframework.stereotype.Service;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@Component
class Engine {
  public String start() {
    return "Engine Started";
  }
}

@Service
class CarService {

  @Autowired
  private Engine engine;

  public String runCar() {
    return engine.start();
  }
}

@RestController
class CarController {

  @Autowired
  private CarService service;

  @GetMapping("/car")
  public String getCarStatus() {
    return service.runCar();
  }
}

// Output (API response):
// Engine Started

• 1 Metadata used in Spring applications.
• 2 Replace XML configuration.
• 3 Used for dependency injection.
• 4 Simplify development.

• 1 @Component – generic bean
• 2 @Service – business logic layer
• 3 @Repository – database layer
• 4 @Controller – MVC controller
• 5 @RestController – REST APIs
• 6 @Autowired – dependency injection
• 7 @Configuration – configuration class
• 8 @Bean – custom bean definition

• 1 Spring scans annotated classes.
• 2 Creates beans automatically.
• 3 Injects dependencies.
• 4 Manages lifecycle of objects.

• 1 Reduces boilerplate code.
• 2 Simplifies configuration.
• 3 Improves readability.
• 4 Faster development.