code: @Override
    public String format(final LogRecord logRecord) {
      this.date.setTime(System.currentTimeMillis());
      return String.format(
          this.logFormat,
          this.date,
          this.trimPrefix(logRecord.getSourceClassName()) + "." + logRecord.getSourceMethodName(),
          logRecord.getLoggerName(),
          logRecord.getLevel().getLocalizedName(),
          formatMessage(logRecord),
          this.getStackTrace(logRecord.getThrown()),
          Thread.currentThread().getName());
    }
docs: Format the log string. Internally, it uses `String.format()` that takes same
  arguments and in the same order as the standard SimpleFormatter, plus the thread name:
  1. date
  2. class and method name
  3. logger name
  4. logging level
  5. message
  6. stack trace
  7. thread name
  
  @return string to be written to the log.