code: public List<InputColumn<?>> getAvailableInputColumns(final Class<?> dataType) {
          final SourceColumnFinder finder = new SourceColumnFinder();
          finder.addSources(this);
          return finder.findInputColumns(dataType);
      }
docs: Finds the available input columns (source or transformed) that match the
  given data type specification.
  
  @param dataType
  the data type to look for
  @return a list of matching input columns