Question

I have a use case where it appears that referencing a Guice injector from multiple locations is the only solution—though this is generally discouraged.

My application is built on top of Talend, an open source ETL platform. Most of my actual application is in Java classes that are called by Talend components. These components include Java snippets that I write and that, in turn, instantiate/invoke my classes.

Now I intend to use Guice throughout my Java classes but there is absolutely no way for me to inject dependencies into the Talend components (so that they would be available to the Java snippets). Instead, I need to actually create these dependencies. I’d like to at least have Guice control the instantiation, which means that instead of using new, it appears that the only way I can instantiate my classes (the ones with @Inject constructors) is to call injector.getInstance. This, in turn, implies that I need to keep the injector around, presumably using an old-fashioned factory that creates it in the first place and makes it available as a singleton.

I just can’t see any other way to handle this but perhaps I’m missing something.

Answer 1

Consider static injection. This will still hide persistent references to your injector across your app, but it will save you from having to pepper your code with injector.getInstance(...) calls. In any case you can inject Injector if you really need to.

class TalendDependencyModule extends AbstractModule {
  @Override public void configure() {
    requestStaticInjection(ExtractorDependencies.class);
    requestStaticInjection(ProcessorDependencies.class);
  }
}

public class ExtractorDependencies {
  @Inject private static Provider<ParserService> parserServiceProvider;
  @Inject private static Provider<SomethingElse> somethingElseProvider;

  private ExtractorDependencies() { }

  static ParserService getParserService() {
    return parserServiceProvider.get();
  }

  /* ... */
}