Telling Guice what Instance to use

[nino martinez wael]

Hi

A couple days ago I wrote to the forum, but I don't think my mail came through.

I have a case where only the code that needs injection can provide one of the objects that needs to be injected :(

The code looks something like this:

Myclass

public myclass(SpecialObject specialObject )
{
--->
InjectorCreator.InjectMembers(this);
}

@inject
public void setController(Controller controller){

}

And lastly the controller class:

Controller{

@inject
public void setSpecialObject(SpecialObject specialObject ){

}

.. @inject a lot of other stuff too

}

So my question are can I somehow make Guice aware of the SpecialObject instance at the ---> marker?

Further the instance reference has to be requestscoped or at least only use the specified instance for the current request only, myclass will only be instantiated once per request .

Regards Nino

[Anton Gavazuk]

you can use a Provider and it will take care creating/getting required instance for injection.

2009/11/24 nino martinez wael <nino.mart...@gmail.com>

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[nino martinez wael]

I know about providers and we are using them alot.

However I fail to see how I can tell a provider to use a specific instance only for that request. Should the pseudo code be something like this:


public myclass(SpecialObject specialObject )
{
--->provider.setInstance(SpecialObject);
InjectorCreator.InjectMembers(

this);
}

How would I get the provider? And how would I makes sure it were only in the current request so we don't get mixed instances over requests..?

regards Nino

2009/11/24 Anton Gavazuk <antong...@gmail.com>

[nino martinez wael]

Ohh and forgot to mention that it is guice 1.0

[Brian Pontarelli]

I'd assume something else is instantiating "myclass" and you need to inject it by hand. In this case, you have a couple of options:

- ThreadLocal

- Singleton/static container

I don't think Providers are scoped (I could be wrong on that) and therefore you can't get the Provider from the injector and then set the value into the provider. Using a ThreadLocal could work if it is safe to assume you are in a single thread. Otherwise, you might have to do some fancy foot work with a singleton or static container to hold the SpecialObject until the Provider can grab it.

-bp

[nino martinez wael]

You assumed correct.

Could you show some pseudo code? Im a bit unsure of how I should use threadlocal.. You can scope a provider, providing you have a scope for it. I don't think a static container would work since, since instances of SpecialObject are request specific..

Thanks for your help so far, interesting point with threadlocal.

regards Nino

2009/11/24 Brian Pontarelli <br...@pontarelli.com>

[Brian Pontarelli]

Code:

public class SpecialObjectHolder {

  public static ThreadLocal< SpecialObject > holder = new ThreadLocal< SpecialObject >();

}

public class MyProvider implements Provider<SomeOtherClass> {

  public SomeOtherClass get() {

    SpecialObject obj = SpecialObjectHolder.holder.get();

    return new SomeOtherClass(obj);

  }

}

public class MyClass {

  @Inject public SomeOtherClass otherClass;

  public MyClass(SpecialObject obj) {

    SpecialObjectHolder.holder.set(obj);

    InjectorCreator.getInjector().injectMembers(this);

  }

}

public class MyModule extends AbstractModule {

  public void bind() {

    bind(SomeOtherClass.class).toProvider(MyProvider.class);

  }

}

That should be roughly what you are looking for.

-bp

[nino martinez wael]

thanks

2009/11/25 Brian Pontarelli <br...@pontarelli.com>