annotated-field-injection.md

layout	title
article	Annotated Field Injection

Injecting into Annotated Fields

This is where a component has an empty constructor with dependencies indicated by a field annotation and provided automatically by the container after instantiation.

public class Apple { 
	@Inject private Orange orange; 
	@Inject private Pear pear; 
	@Inject private Banana banana; 
	// methods 
}

Usage

pico = new DefaultPicoContainer(new AnnotatedFieldInjection();
pico.addComponent(Apple.class); // etc
Apple apple = pico.getComponent(Apple.class);

With an custom annotation instead of PicoContainer's @Inject

pico = new DefaultPicoContainer(new AnnotatedFieldInjection(MyInjectAnnotaton.class);
pico.addComponent(Apple.class); // etc Apple apple = pico.getComponent(Apple.class);

Yes that's right, there's no constructor needed. It means that for a Unit Test, you cannot simply 'new' the class without some magic to populate the dependency fields.

The component factory for this is a class AnnotatedFieldInjection . It only handles annotation-field injection for components.

Additionally the default component factory AdaptiveInjection can also handle field annotation types, if the @Inject annotation from PicoContainer's code-base is used as the marker for injection. AdaptiveInjection will also fall through to constructor injection if there is no recognized `Inject annotation.