@ConditionalOnProperty Annotation on Spring boot

This annotation is help to create bean based on condition using some property , it is a class level annotation , to create a bean we can use this code

@ConditionalOnProperty(prefix = "carservice1", value = "enabled", havingValue = "true", matchIfMissing = false)

to create s bean of this class we have to add a property in application.property file

prefix.value is a key and havingValue is value of key

and if value is miss-matched then bean will not be created due to matchIfMissing = false

example: carservice1.enable = true

this value should match with havingValue field then only the bean will be created

let's understand this using code example

// let's suppose i want to create two service and both service has implemented the common method createCar(). and i want to call a method of any service

// Car Service Interface

public interface CarService {
	public void createCar();
}

@Component
@ConditionalOnProperty(prefix = "carservice1", value = "enabled", havingValue = "true", matchIfMissing = false)
public class Service1 implements CarService{
	public Service1() {
		System.out.println("Service1 created");
	}

	@Override
	public void createCar(){
		System.out.println("Car is created by service1");
	}
}

@Component
@ConditionalOnProperty(prefix = "carservice2", value = "enabled", havingValue = "true", matchIfMissing = false)
public class Service2 implements CarService {
	public Service2() {
		System.out.println("Service2 is created");
	}

	@Override
	public void createCar() {
		System.out.println("Car is created by service2");
	}
}

// in this CreateCarService i wanted to inject Service1 and Service2 using autowired annotation

here i have added attribute required = false so it will not throw an error when bean is not found

@Service
public class CreateCarService {
	@Autowired(required = false)
	private Service1 carService1;
	@Autowired(required = false)
	private Service2 carService2;

	@PostConstruct
	public void init() {
		System.out.println("init method");
		System.out.println("Service1: " + carService1);
		System.out.println("Service2: " + carService2);
	}

	public CarService getCarService() {
		if (carService1 != null) {
			return carService1;
		} else if (carService2 != null) {
			return carService2;
		} else {
			throw new IllegalStateException("No CarService implementation available");
		}
	}
}

Main Method to user this implementation

public static void main(String[] args) {
		CreateCarService createCarService = new CreateCarService();
		CarService carService = createCarService.getCarService();
		carService.createCar();
	}

note : before using this code we have to add property then only service1 bean will be created

carservice1.enable=true

Output: Car is created by service1