Ninjector

= Ninjector

Ninjector is the cure for a disease called Field Injection Anxiety, widely diagnosed amongst software developers that care about their code. The disease is caused by injection frameworks all too easily allowing http://www.martinfowler.com/articles/injection.html[dependency injection] into a class' fields which seems to be a convenient thing to do in the first place but will inevitably bite you in the back later on. For a more detailed analysis of symptoms and consequences, see http://olivergierke.de/2013/11/why-field-injection-is-evil[this blog post]

== What does it do?

@Configuration
@ComponentScan
@DisableFieldInjection
class Application { … }

/**
 * This class will fail the ApplicationContext to bootstrap
 * due to the injection annotation used on a field.
 **/
@Component
class ApplicationComponent {

  @Autowired MyCollaborator collaborator;
}

@DisableFieldInjection registers a tiny Spring extension that will pre-process the bean instances about to be created, scan their fields for common injection annotations (e.g. @Inject, @Autowired, @Resource) and reject the bean instantiation right away.