Using @Assisted inject with multiple params of same Type (@Named params)

Question

my problem boils down to using @Assisted with two string arguments to the factory. The problem is that because Guice treats type as the identification mechanism for parameters, both parameters are the same, and I get a configuration error.

Some Code:

public class FilePathSolicitingDialog {      //... some fields      public static interface Factory {         public FilePathSolicitingDialog make(Path existingPath,                                              String allowedFileExtension,                                              String dialogTitle);     }      @Inject     public FilePathSolicitingDialog(EventBus eventBus,                                     SelectPathAndSetTextListener.Factory listenerFactory,                                     FilePathDialogView view,                                     @Assisted Path existingPath,                                     @Assisted String allowedFileExtension,                                     @Assisted String dialogTitle) {         //... typical ctor, this.thing = thing     }      // ... methods } 

The problem lies in the double-strings parameters.

I've tried tagging each string with separate @Named("as appropriate") annotations, but that just leads to more configuration errors. From the sound of those errors they don't want binding annotations on the factory class, so I have not tried custom binding annotations.

The simple and noisy solution is to create a simple argument class to contain those three assisted values, and simply inject that:

    public static class Config{         private final Path existingPath;         private final String allowedFileExtension;         private final String dialogTitle;          public Config(Path existingPath, String allowedFileExtension, String dialogTitle){             this.existingPath = existingPath;             this.allowedFileExtension = allowedFileExtension;             this.dialogTitle = dialogTitle;         }     }      public static interface Factory {         public FilePathSolicitingDialogController make(Config config);     }      @Inject     public FilePathSolicitingDialogController(EventBus eventBus,                                               SelectPathAndSetTextListener.Factory listenerFactory,                                               FilePathDialogView view,                                               @Assisted Config config) {         //reasonably standard ctor, some this.thing = thing         // other this.thing = config.thing     } } 

This works and is likely to be fairly bug-free but is noisy. Some way to get rid of that nested static class would be nice.

Thanks for any help!

Answer 1

Have a look at this documentation (previously here):

Making parameter types distinct

The types of the factory method's parameters must be distinct. To use multiple parameters of the same type, use a named @Assisted annotation to disambiguate the parameters. The names must be applied to the factory method's parameters:

public interface PaymentFactory {    Payment create(        @Assisted("startDate") Date startDate,        @Assisted("dueDate") Date dueDate,        Money amount);  } 

...and to the concrete type's constructor parameters:

public class RealPayment implements Payment {    @Inject    public RealPayment(       CreditService creditService,       AuthService authService,       @Assisted("startDate") Date startDate,       @Assisted("dueDate") Date dueDate,       @Assisted Money amount) {      ...    }  }