Getting an instance within a Guice Module

Question

I have this class:

public class CompositeSecurityAuthorizer implements SecurityAuthorizer {
    @inject @CompositeSecurityAuthorizerAnnot
    List<SecurityAuthorizer> authorizers; //Field Injection
}

I want to inject the authorizers field a List<SecurityAuthorizer> value.

In my module , I have the following:

@Override
protected void configure() {
  bind(CompositeSecurityAuthorizer.class).in(Singleton.class);
  bind(StoreAuthorizer.class).in(Singleton.class);
  bind(SecurityAuthorizer.class)
      .annotatedWith(CompositeSecurityAuthorizerAnnot.class)
      .to(CompositeSecurityAuthorizer.class);
}

@Provides @CompositeSecurityAuthorizerAnnot
List<SecurityAuthorizer> provideAuthorizersList()
{
    List<SecurityAuthorizer> authList = new ArrayList<SecurityAuthorizer>();
    //How do I add StoreAuthorizer while maintaining a Singleton?
    //Will the line below do it through Guice magic?
    //authList.add(new StoreAuthorizer());
    return authList;
}

---

My question is embedded in the code comments. When I'm adding StoreAuthorizer to that List<SecurityAuthorizer>:

• How do I ensure it's the same instance as other StoreAuthorizer references?
• Is that something Guice is just doing under the hood, so new StoreAuthorizer() really is calling an impl of getInstance() behind the scenes?

Answer 1

Provider methods allow injected arguments. The StoreAuthorizer passed to the method here will be the singleton bound in your module. Guice doesn't and can't do anything magical if you call a constructor yourself.

@Provides @CompositeSecurityAuthorizerAnnot
List<SecurityAuthorizer> provideAuthorizersList(StoreAuthorizer storeAuthorizer)
{
    List<SecurityAuthorizer> authList = new ArrayList<SecurityAuthorizer>();
    authList.add(storeAuthorizer);
    return authList;
}

As an aside, you may want to consider using the Guice Multibindings extension to create a Set<SecurityAuthorizer> rather than doing this yourself.