How to build a function call without input parameter in spring AI

Question

I tried to define a function call in Spring AI:

@Bean
@Description("return list of Vets, include their specialist")
public Function<Void, Collection<Vet>> queryVets() {
    return request -> {
        return vetRepository.findAll();
    };
}

The input parameter is Void as the function has no input parameter.

But I got the error:

com.azure.core.exception.HttpResponseException: Status code 400,

{
   "error": {
   "message": "Invalid schema for function 'queryVets': In context=(), object schema missing properties",
   "type": "invalid_request_error",
   "param": null,
   "code": null
  }
}

How can I define a function without input parameters?

Answer 1

Starting with 1.0.0-M4, Spring AI provides support for functions without input parameters. You can use both Supplier<O> or Function<Void, O> more here. Also you can use plain Java Methods without input parameters:

FunctionCallback callback = FunctionCallback.builder()
    .description("Get weather information for a city")
    .method("getWeather") // method name with empty varargs argument types
    .targetClass(WeatherService.class)
    .build();

Find more about the plain method invoking here.