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Accessing Services managed by the Injector

The injector is responsible for constructing and linking components together. In many scenarios, it is desirable for the injector to expose services so that they can be accessed by the host application. This is done by adding an "output" method on the injector. The methods must be an abstract instance method that returns the desired service. The annotation processor will treat these methods as dependencies that must be resolved. These methods can also return qualified services if they are annotated with the @Named annotation as described in the naming document. These output methods can also be the different types of dependency described in the dependency kinds document.

When resolving an output, Sting treats primitive and boxed equivalents as the same service. A request for Integer can be satisfied by an int provider and a request for int can be satisfied by a non-null Integer provider. However, a nullable boxed provider still does not satisfy a required primitive or required boxed request, and if both primitive and boxed providers exist for the same qualifier then singular outputs remain ambiguous while collection outputs contain both bindings.

A simple example to illustrate how services can be accessed from an injector follows.

The injector:

@Injector
public interface LibraryApplication
{
  static LibraryApplication create()
  {
    return new Sting_LibraryApplication();
  }

  BookCatalog getBookCatalog();
}

Using the injector from the host application:

{
  final LibraryApplication application = LibraryApplication.create();
  final BookCatalog bookCatalog = application.getBookCatalog();

  // Lookup Hitchiker's Guide to the Galaxy
  final Book book = bookCatalog.queryByIsbn( "0434023396" );
  if ( null != book )
  {
    System.out.println( "Huzzah! The book is available" );
  }