Why you have to anotate classes in Spring boot with service etc.?

Question

Everyone says that it's because spring boot in that case will know that service exists. But if you call that service's method in another method that you try to run when the web app is running. Should it know the service exists without the annotation or not?

Answer 1

The main reason you put these stereotype annotations to classes is creating beans in application context and let the IOC container to provide the management and configuration of these beans depending on their stereotypes.

Spring is an IOC container responsible for instantiating, configuring and assembling these beans. And putting stereotype annotation is just a way to define bean.

You can define beans in various ways such as using @Bean annotation, stereotype annotations, XML definitions etc. and if you don't define your bean, the IOC container can not detect and instantiate the service.