inject

Simple java dependency injection framework based on the ServiceLoader API.

Sample

First we define a bean of name SingletonServiceImpl.

@Ordered(1)
@Singleton
public class SingletonServiceImpl implements SingletonService {

	@Inject
	private PrototypeBean prototype;

	public SingletonServiceImpl() {
		System.out.println(this.getClass().getName() + " instantiated");
	}

	@Override
	public PrototypeBean getInjectedBean() {
		return prototype;
	}
}

Later on we access it directly using the name, or by providing the interface:

final var singleton1 = Context.instance().getBean("SingletonServiceImpl", SingletonService.class);
final var singleton2 = Context.instance().getBean(SingletonService.class);

assertEquals(singleton1, singleton2);
assertNotNull(singleton1.getInjectedBean());

Although we didn't implement the singleton pattern in our SingletonServiceImpl, we will always get the same instance!

In case there are multiple bean implementing the same interface, the @Ordered annotation is used to determine the right bean - the lower the value the higher the load priority.

Dependency injection

All fields annotated with @Injected will be injected on bean-creation. There are several ways how this is done:

Compile-time-weaving using the io.spotnext.inject.instrumentation.InjectionTransformer with the maven mojo io.spot-next:spot-maven-plugin
Load-time-weaving using DynamicInstrumentationLoader.initialize(InjectionTransformer.class); from the library io.spot-next:spot-instrumentation
No weaving. If the beans dependencies have not yet injected by the class transformer the dependencies will be injected after the bean instantiation via reflection. This is perfectly fine although it has the downside that the fields are null in the constructor call. The very same mechanism (Context.getInstance).injectBeans(bean) can be used on manually created objects

mojo2012/inject

inject

Sample

Dependency injection