code: public synchronized String formatMessage(LogRecord record) {
          String format = record.getMessage();
          java.util.ResourceBundle catalog = record.getResourceBundle();
          if (catalog != null) {
              try {
                  format = catalog.getString(record.getMessage());
              } catch (java.util.MissingResourceException ex) {
                  // Drop through.  Use record message as format
                  format = record.getMessage();
              }
          }
          // Do the formatting.
          try {
              Object parameters[] = record.getParameters();
              if (parameters == null || parameters.length == 0) {
                  // No parameters.  Just return format string.
                  return format;
              }
              // Is it a java.text style format?
              // Ideally we could match with
              // Pattern.compile("\\{\\d").matcher(format).find())
              // However the cost is 14% higher, so we cheaply check for
              // 1 of the first 4 parameters
              if (format.indexOf("{0") >= 0 || format.indexOf("{1") >=0 ||
                          format.indexOf("{2") >=0|| format.indexOf("{3") >=0) {
                  return java.text.MessageFormat.format(format, parameters);
              }
              return format;
  
          } catch (Exception ex) {
              // Formatting failed: use localized format string.
              return format;
          }
      }
docs: Localize and format the message string from a log record.  This
  method is provided as a convenience for Formatter subclasses to
  use when they are performing formatting.
  <p>
  The message string is first localized to a format string using
  the record's ResourceBundle.  (If there is no ResourceBundle,
  or if the message key is not found, then the key is used as the
  format string.)  The format String uses java.text style
  formatting.
  <ul>
  <li>If there are no parameters, no formatter is used.
  <li>Otherwise, if the string contains "{0" then
  java.text.MessageFormat  is used to format the string.
  <li>Otherwise no formatting is performed.
  </ul>
  <p>
  
  @param  record  the log record containing the raw message
  @return   a localized and formatted message