code: public static Collection<String> getConversionProviderNames(){
          Collection<String> providers = getMonetaryConversionsSpi().getProviderNames();
          if(Objects.isNull(providers)){
              Logger.getLogger(MonetaryConversions.class.getName()).warning(
                      "No supported rate/conversion providers returned by SPI: " +
                              getMonetaryConversionsSpi().getClass().getName());
              return Collections.emptySet();
          }
          return providers;
      }
docs: Return the (non localized) names of all providers available in the
  current context. Each id can be used to obtain
  {@link ExchangeRateProvider} or {@link CurrencyConversion} instances.
  
  @return all supported provider ids, never {@code null}.