Assisted injection support

[natros]

Hi,

I'm trying to convert a project that uses dagger 2 to micronaut. One thing the dagger supports is assisted injection (another injection framework that supports assisted injection is Guice). Does micronaut support this?

This is the example that I am trying to convert.

import dagger.assisted.Assisted;
import dagger.assisted.AssistedFactory;
import dagger.assisted.AssistedInject;

public class DialogBox {
  private final Messages messages;

  @AssistedInject
  DialogBox(Messages messages, @Assisted String caption) {
    this.messages = messages;
    messages.log(String.format("creating DialogBox(%s)", caption));
  }

  public void show() {
    messages.log("show dialog");
  }

  @AssistedFactory
  public interface Factory {
    DialogBox create(String caption);
  }
}

public class App {
  private final DialogBox.Factory dialogBoxFactory;

  @Inject
  App(DialogBox.Factory dialogBoxFactory) {
    this.dialogBoxFactory = dialogBoxFactory;
  }

  public void run() {
    DialogBox dlg1 = dialogBoxFactory.create("dlg1");
    DialogBox dlg2 = dialogBoxFactory.create("dlg2");
  }
}

[graemerocher]

closest thing here is parameterized beans:

import jakarta.inject.*;
import io.micronaut.context.annotation.*;

@Singleton
public class DialogBox {
  private final Messages messages;

  @Inject
  DialogBox(Messages messages, @Parameter String caption) {
    this.messages = messages;
    messages.log(String.format("creating DialogBox(%s)", caption));
  }

  public void show() {
    messages.log("show dialog");
  }

  public interface Factory {
    DialogBox create(String caption);
  }

  @Singleton  
  class FactoryImpl implements Factory {
        private final BeanContext context;
        FactoryImpl(BeanContext context) {
            this.context = context;
       }
       @Override
       public DialogBox create(String caption) {
            context.createBean(DialogBox.class, caption);
       }
  }
}

If you don't want to implement the factory you could write introduction advice that implements it for you:

@Introduction
@Retention(RUNTIME)
public @interface Assisted {
}

@Assisted
public interface Factory {
    DialogBox create(String caption);
}

@InterceptorBean(Assisted.class)
class AssistedInterceptor implements MethodInterceptor<Object, Object> {
        private final BeanContext context;
        AssistedInterceptor(BeanContext context) {
             this.context = context;
        } 

       @Override
       public Object intercept(InvocationContext context) {
              var beanType = context.getReturnType().getType();
               return context.createBean(beanType, context.getParameterValues());
       }
}

[natros]

Wow!

It's amazing how easily you can implement very useful generic functionality with very little code.

I made a small correction (I'm testing with micronaut 3.7.4)

@InterceptorBean(Assisted.class)
class AssistedInterceptor implements MethodInterceptor<Object, Object> {
  private final BeanContext context;

  AssistedInterceptor(BeanContext context) {
    this.context = context;
  }

  @Nullable
  @Override
  public Object intercept(MethodInvocationContext<Object, Object> invocationContext) {
    Class<?> beanType = invocationContext.getReturnType().getType();
    return context.createBean(beanType, invocationContext.getParameterValues());
  }
}