code: protected static void extractSubProperties (Properties source, Properties dest, String prefix)
      {
          // extend the prefix to contain a dot
          prefix = prefix + ".";
          int preflen = prefix.length();
  
          // scan the source properties
          Enumeration<?> names = source.propertyNames();
          while (names.hasMoreElements()) {
              String name = (String)names.nextElement();
              // skip unrelated properties
              if (!name.startsWith(prefix)) {
                  continue;
              }
              // insert the value into the new properties minus the prefix
              dest.put(name.substring(preflen), source.getProperty(name));
          }
      }
docs: A helper function used by the {@link #getSubProperties} methods.