How to avoid having injector.createInstance() all over the place when using guice?

Question

There\'s something I just don\'t get about guice: According to what I\'ve read so far, I\'m supposed to use the Injector only in my bootstrapping class (in a standalone appl

Answer 1

Yes, you basically only should use the Injector to create get the instance for the root-object. The rest of the application shouldn't touch the Guice-Container. As you've noticed, you still need to create some objects when required. There are different approaches for doing that, each suitable for different needs.

Inject a Provider Provider is a interface from Guice. It allows you to request a new instance of a object. That object will be created using Guice. For example.

 class MyService{
     private Provider transactionProvider;
     public MainGui(Provider transactionProvider){
         this.transactionProvider = transactionProvider;
     }

     public void actionStarted(){
         Transaction transaction = transactionProvider.get();
     }

Build a Factory Often you need some kind of factory. This factory uses some injected services and some parameters and creates a new object for you. Then you use this factory for new instances. Then you inject that factory and use it. There also help for this with the AssistedInject-extension

I think with these two possibilities you rarely need to use the Guice-Injector itself. However sometimes is still appropriate to use the injector itself. Then you can inject the Injector to a component.