code: public void getSubProperties (String prefix, Properties target)
      {
          // slap a trailing dot on if necessary
          if (!prefix.endsWith(".")) {
              prefix = prefix + ".";
          }
  
          // build the sub-properties
          for (Iterator<String> iter = keys(); iter.hasNext(); ) {
              String key = iter.next();
              if (!key.startsWith(prefix)) {
                  continue;
              }
              String value = getValue(key, (String)null);
              if (value == null) {
                  continue;
              }
              target.put(key.substring(prefix.length()), value);
          }
      }
docs: Fills into the supplied properties object all configuration values that start with the
  supplied prefix (plus a trailing "." which will be added if it doesn't already exist). The
  keys in the sub-properties will have had the prefix stripped off.