Identify component factories by identifier string

[kevinwallimann]

Description
Currently, component factories are loaded in ClassLoaderUtils given their fully qualified classnames. The classname is passed by the configuration. (e.g. component.writer)

That means that components don't have the possibility to be refactored (renaming, moving to a different package) without introducing a breaking change which would require updating any existing configuration that uses that component.

Tasks

• Add a method getIdentifier: String to the interface ComponentFactory. getClass.getName may be used as a default value. (so this feature won't be a breaking change)
• Implementing components are responsible for providing a unique identifier. It's advisable to prefix the identifier with a human readable name, because it will be referenced in the configuration, logged, etc..
• Use getIdentifier to load the factory in ClassLoaderUtils. Currently, it loads the class directly given the class name. This approach doesn't work to efficiently load the factory by the identifier. With Configuration property keys of components should be accessible via reflection #83, component factories can be loaded using the Service Provider Interface (SPI), i.e. with ServiceLoader. All factories expose the getIdentifier method, that's how it can be found

Other

• The same identifier might be used by each component to prefix its configuration properties to avoid name clashes.