I am bit confused about following things. I understand @Service
and @Component
annotations are main annotations when we define a component or a service
A service can be published without a @Component
annotation, but you have to do it programmatically. If you use the annotation then you benefit from the automatic metadata generation in the build tool, and also from the Declarative Services runtime framework. This simplifies a lot of things. If you want to do it with low-level code you have to write an implementation of BundleActivator
, declare that with the Bundle-Activator
manifest header, call context.registerService
etc. Bottom line: just use the @Component
annotation!
Simple: laziness. When a component is a service then it can be instantiated lazily "on-demand", i.e. only when consumer first tries to use the service. Non-service components, on the other hand, usually do other kinds of things inside themselves, e.g. running a web server or a GUI or a polling thread, whatever. These need to be running all the time, rather than on-demand.
3. I didn't understand this question.