Question

how to change/set a binding by a property/string given in a property/text file? in my case i want to implement a kind of “demo mode”.
In normal mode a property gives an url to an external service but if url is “demo” the binding of the according interface should be changed like this:

normal:

bind(SasDatenProvider.class).to(SasDataProviderHttpImpl.class);

demo

bind(SasDataProvider.class).to(SasDataProviderFileImpl.class);

how to achieve that?
thx in advance

Answer 1

You can use a method annotated with @Provides in your module. Then you can do something like this:

public class MyModule extends AbstractModule {

    @Provides
    SasDatenProvider provideSas(SasDataProviderHttpImpl http, 
        SasDataProviderFileImpl file){

        boolean isDemo = false; /* do you property lookup logic here */

        return isDemo ? file : http;
    }
}

You can read more about @Provides-methods in the guice docs:
http://code.google.com/p/google-guice/wiki/ProvidesMethods

If your don’t want this kind of logic in you module, you can consider creating your own provider:
http://code.google.com/p/google-guice/wiki/ProviderBindings