In my spring cloud function application I’ve created a custom message converter.

I am converting from JSON to HapiFhir Bundle.class and then from the Bundle.class back to JSON.

The convertFromInternal method works as expected. It successfully converts the JSON to the Bundle.class

However, convertToInternal never gets invoked…

I debugged the code and found that the SimpleFunctionRegistry.class calls a method convertOutPutIfNecessary… this class requires String[] contentType

The contentType is not set and subsequently does not trigger my custom convertToInternal method.

The Bundle.class is just .toString() as the output message. This is converted to JSON but not the correct JSON formatted message, hence why I created custom message converter.

I cannot determine how or where the contentType value is set in the SimpleFunctionRegistry.class

Am I using the CustomMessageConverter Correctly?

Below is my CustomMessageConverter class

public MyCustomMessageConverter() {
    super(new MimeType("application", "json+fhir"), new MimeType("application", "json"));
  }

  @Override
  protected boolean supports(Class<?> clazz) {
    return (Bundle.class.equals(clazz));
  }

  @Override
  protected Object convertFromInternal(Message<?> message, Class<?> targetClass, Object conversionHint) {
    Object payload = message.getPayload();
    FhirContext ctx = FhirContext.forR4();
    return ctx.newJsonParser().parseResource(Bundle.class, (String) payload);
  }

  @Override
  protected Object convertToInternal(Object payload, MessageHeaders headers, Object conversionHint) {
    FhirContext ctx = FhirContext.forR4();
    return ctx.newJsonParser().encodeResourceToString((Bundle) payload);
  }
}