jooby/src/main/java/org/jooby/RequestLogger.java
public RequestLogger dateFormatter(final Function<Long, String> formatter) {
    requireNonNull(formatter, "Formatter required.");
    this.df = formatter;
    return this;
  }
public RequestLogger dateFormatter(final Function<Long, String> formatter) {
    requireNonNull(formatter, "Formatter required.");
    this.df = formatter;
    return this;
  }
Override the default date formatter.

@param formatter New formatter to use.
@return This instance.