code: public static String resolvePlaceholders(Properties properties, String text) {
          if (text == null) {
              return text;
          }
          return parseStringValue(properties, text, text, new HashSet<String>());
      }
docs: Resolve ${...} placeholders in the given text, replacing them with corresponding
  system property values.
  
  @param properties a properties instance to use in addition to System
  @param text       the String to resolve
  @return the resolved String
  @throws IllegalArgumentException if there is an unresolvable placeholder
  @see #PLACEHOLDER_PREFIX
  @see #PLACEHOLDER_SUFFIX