A tip in Spring IOC

These days, I’m learning how Apache Kafka is used in Springboot. And I found an interesting tip in Springboot ioc.

Before, I injected the bean into another bean like this:

@Service
public class KafkaProducer {
    
    private KafkaTemplate<String, String> kafkaTemplate;

    @Autowired
    public KafkaProducer(KafkaTemplate<String, String> kafkaTemplate) {
        this.kafkaTemplate = kafkaTemplate;
    }
}

Or like this:

@Service
public class KafkaProducer {
    
    @Autowired
    private KafkaTemplate<String, String> kafkaTemplate;
}

But, when I learned with this tutorial, the author inject the kafkaTemplate like this:

@Service
public class KafkaProducer {
    
    private KafkaTemplate<String, String> kafkaTemplate;

    public KafkaProducer(KafkaTemplate<String, String> kafkaTemplate) {
        this.kafkaTemplate = kafkaTemplate;
    }
}

In other words, this way of injecting without @Autowired, made me feel amazed.

He said Spring framework will automatically inject this dependency(kafkaTemplate) whenever this bean(KafkaProducer) has only one parameterized constructor. I think is a useful and elegant way.