Edit

Dependency Injection

Arez components provide additional support when integrating into the Sting dependency injection framework. Although historically Arez has been used with both Dagger2 and Gin.

Arez components require dependencies to be passed in as constructor parameters. (Historically Arez supported field and method injection but this frequently produced inefficient code and confused component authors as different frameworks would inject components in different orders depending on whether they were declared in superclasses or in the arez component and whether they used field or method injection).

Arez components consist of the authored component (i.e. com.example.MyService) and the generated component class produced by the Arez annotation processor (i.e. com.example.Arez_MyService). When consuming an Arez component, the consuming component should use the authored component (i.e. com.example.MyService) when consuming the component.

Every injection framework uses a slightly different mechanism to determine how to construct and wire together a graph of objects. The following sections describe the two frameworks that have builtin support within Arez.

Sting

Sting is a fast, easy to use, compile-time dependency injection toolkit. The toolkit accepts a set of annotated java classes and generates source code to instantiate and wire together the components. Sting was heavily inspired by Dagger2 but with a better developer-experience and more efficient code generation. See the dagger comparison for some reasons why it is considered a better fit in the context of web applications. Sting models the application as a set of components that are contained within an injector. An injector is responsible for constructing and linking components together.

The @ArezComponent annotation has a sting parameter that controls whether the Arez annotation processor adds sting annotations onto the generated component class. If the value of the sting parameter is ENABLE or AUTODETECT and the sting.Injector class is on the classpath then the annotations will be added.

The Arez component author can also add the @Eager, @Typed and @Named annotations from Sting onto the component and these will be copied to the generated component class. The Arez component can be registered with the injector via the includes parameter of the injector. (Although the next release of Sting will eliminate this requirement.)

@Injector( includes = MyService.class )
public interface ExampleStingInjector
{
  ExampleConsumer getExampleConsumer();
}

The injector can then be used in code like:

final ExampleStingInjector component = new Sting_ExampleStingInjector();
component.getExampleConsumer().performSomeAction( 42 );