How to use

isAvailable

method

in

javax.money.convert.ExchangeRateProvider

/**
 * Checks if an {@link ExchangeRate} between two {@link CurrencyUnit} is
 * available from this provider. This method should check, if a given rate
 * is <i>currently</i> defined.
 *
 * @param baseCode the base currency code
 * @param termCode the terminal/target currency code
 * @return {@code true}, if such an {@link ExchangeRate} is currently
 * defined.
 * @throws MonetaryException if one of the currency codes passed is not valid.
 */
default boolean isAvailable(String baseCode, String termCode){
  return isAvailable(Monetary.getCurrency(baseCode), Monetary.getCurrency(termCode));
}

@Override
public ExchangeRate getExchangeRate(ConversionQuery conversionQuery) {
  for (ExchangeRateProvider prov : this.providers) {
    try {
      if (prov.isAvailable(conversionQuery)) {
        ExchangeRate rate = prov.getExchangeRate(conversionQuery);
        if (Objects.nonNull(rate)) {
          return rate;
        }
      }
    } catch (Exception e) {
      Logger.getLogger(getClass().getName()).log(Level.WARNING,
          "Rate Provider did not return data though at check before data was flagged as available," +
              " provider=" + prov.getContext().getProviderName() + ", query=" + conversionQuery);
    }
  }
  throw new CurrencyConversionException(conversionQuery.getBaseCurrency(), conversionQuery.getCurrency(), null,
      "All delegate prov iders failed to deliver rate, providers=" + this.providers +
          ", query=" + conversionQuery);
}

/**
 * Checks if an {@link ExchangeRate} between two {@link CurrencyUnit} is
 * available from this provider. This method should check, if a given rate
 * is <i>currently</i> defined.
 *
 * @param base the base {@link CurrencyUnit}
 * @param term the term {@link CurrencyUnit}
 * @return {@code true}, if such an {@link ExchangeRate} is currently
 * defined.
 */
default boolean isAvailable(CurrencyUnit base, CurrencyUnit term){
  return isAvailable(ConversionQueryBuilder.of().setBaseCurrency(base).setTermCurrency(term).build());
}

/**
 * The method reverses the {@link ExchangeRate} to a rate mapping from term
 * to base {@link CurrencyUnit}. Hereby the factor must <b>not</b> be
 * recalculated as {@code 1/oldFactor}, since typically reverse rates are
 * not symmetric in most cases.
 *
 * @return the matching reversed {@link ExchangeRate}, or {@code null}, if
 * the rate cannot be reversed.
 */
default ExchangeRate getReversed(ExchangeRate rate){
  ConversionQuery reverseQuery = rate.getContext().toQueryBuilder().setBaseCurrency(rate.getCurrency())
      .setTermCurrency(rate.getBaseCurrency()).build();
  if(isAvailable(reverseQuery)){
    return getExchangeRate(reverseQuery);
  }
  return null;
}