CODEWITHSUNDEEP
javaguice
Ritesh Modi
Ritesh Modi

Reputation: 53

Guice linked binding versus @Provides method

I have this problem.

Consider I have classes definitions like:

public interface ABCInterface 
{
}

And its implementation:

public class ABCImpl 
{       
  @Inject
  private XYZ xyz;
}

When the Guice Config is like this:

public class MasterConfig extends AbstractModule 
{    
  @Override
  protected void configure() 
  {
    // TODO Auto-generated method stub
    bind(ABCInterface.class)
    .to(ABCImpl.class);
  }
}

And run it, then everything works fine and XYZ gets injected into it.

But when I use provider methods like this:

public class MasterConfig extends AbstractModule {

    @Override
    protected void configure() {
        // TODO Auto-generated method stub
    }

    @Provides
    public ABCInterface abc() {
        return new ABCImpl();
    }
}

Then, in this case, I get a null pointer exception when I try to use the injected XYZ, because that object remains null. I am suspecting, this is beacuse, I am returning a new object of ABCImpl and hence Guice is not able to build a dependency graph. Please correct me if I am wrong here?

Can anyone suggest, how to write the Provider method, so that everything gets injected properly like it does when I mention in the configure method.

Upvotes: 3

Views: 2819

Answers (1)

Tavian Barnes
Tavian Barnes

Reputation: 12922

Indeed, when you write new ABCImpl(), Guice doesn't get a chance to inject its dependencies. You can do this:

@Provides
ABCInterface abc(ABCImpl impl) {
    return impl;
}

but you might as well just write bind(ABCInterface.class).to(ABCImpl.class); in that case, unless your provider method has some extra logic.

Upvotes: 3

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