add convenience methods for getting multi-valued properties

The existing Config API only permits retrieving multi-valued properties as arrays like this:

for (String value : config.getValue("my.key", String[].class)) {
    // do something with value
}

I propose we add the following methods to permit retrieving more than one value in a more natural way:

<T> Iterable<T> getValues(String propertyName, Class<T> propertyType);
    
<T> Optional<Iterable<T>> getOptionalValues(String propertyName, Class<T> propertyType);

This would enable the use of lamba-friendly patterns like this:

config.getValues("my.key", String.class)
      .forEach(value -> {
            // do something with value
      });

As a bonus, the developer doesn’t need to worry about asking for String.class or String[].class depending on the scenario.

[emattheis]

That works for me. Not sure which hacky way is best for obtaining the array class in the default implementation, but the Array#newInstance approach seems like the cleanest since there are no magic string formulas or checked exceptions to deal with.

default <T> List<T> getValues(String propertyName, Class<T> propertyType) {
    @SuppressWarnings("unchecked")
    Class<T[]> arrayType = (Class<T[]>) Array.newInstance(propertyType, 0).getClass();
    return Arrays.asList(getValue(propertyName, arrayType));
}

default <T> Optional<List<T>> getOptionalValues(String propertyName, Class<T> propertyType) {
    @SuppressWarnings("unchecked")
    Class<T[]> arrayType = (Class<T[]>) Array.newInstance(propertyType, 0).getClass();
    return getOptionalValue(propertyName, arrayType).map(Arrays::asList);
}

[Emily-Jiang]

The PR #501 has been merged a while ago.