velocity 调用自定义方法，日期函数为例
toolbox.xml

  $date                         -> Oct 19, 2003 9:54:50 PM
  $date.long                    -> October 19, 2003 9:54:50 PM PDT
  $date.medium_time             -> 9:54:50 PM
  $date.full_date               -> Sunday, October 19, 2003
  $date.get('default','short')  -> Oct 19, 2003 9:54 PM
  $date.get('yyyy-M-d H:m:s')   -> 2003-10-19 21:54:50

 Example of formatting an arbitrary date:
  $myDate                        -> Tue Oct 07 03:14:50 PDT 2003
  $date.format('medium',$myDate) -> Oct 7, 2003 3:14:50 AM