Delphi的怎么获取当前的时间并且转换为精确到毫秒

最近有一个任务（使用Delphi开发），需要获取时间，并且精确到毫秒，并以人性化的方式展示出来，比如2015-08-17 19:32:00 800

   var
    currentTime:TSystemTime;
    year, month, day, hour, minute, second, millisecond: string;
    datetime: string;
  begin
    GetSystemTime(currentTime);
    year:= IntToStr(currentTime.wYear);
    month:= IntToStr(currentTime.wMonth);
    day:= IntToStr(currentTime.wDay);
    hour:= IntToStr(currentTime.wHour);
    minute:= IntToStr(currentTime.wMinute);
    second:= IntToStr(currentTime.wSecond);
    millisecond:= IntToStr(currentTime.wMilliseconds);

    datetime:= year + '-' + month + '-' + day + ' ' + hour + ':' + minute + ':' + second + ':' + millisecond;
    ShowMessage(datetime);
  end;

其中TSystemTime的定义为

   PSystemTime = ^TSystemTime;
  _SYSTEMTIME = record
    wYear: Word;
    wMonth: Word;
    wDayOfWeek: Word;
    wDay: Word;
    wHour: Word;
    wMinute: Word;
    wSecond: Word;
    wMilliseconds: Word;
  end;
  {$EXTERNALSYM _SYSTEMTIME}
  TSystemTime = _SYSTEMTIME;
  SYSTEMTIME = _SYSTEMTIME;
  {$EXTERNALSYM SYSTEMTIME}

var
currentTime:TSystemTime;
year, month, day, hour, minute, second, millisecond: string;
datetime: string;
begin
GetSystemTime(currentTime);
year:= IntToStr(currentTime.wYear);
month:= IntToStr(currentTime.wMonth);
day:= IntToStr(currentTime.wDay);
hour:= IntToStr(currentTime.wHour);
minute:= IntToStr(currentTime.wMinute);
second:= IntToStr(currentTime.wSecond);
millisecond:= IntToStr(currentTime.wMilliseconds);

datetime:= year + '-' + month + '-' + day + ' ' + hour + ':' + minute + ':' + second + ':' + millisecond;
Form1.mmo1.Lines.Add(datetime);

end;

其中TSystemTime的定义是：
PSystemTime = ^TSystemTime;
_SYSTEMTIME = record
wYear: Word;
wMonth: Word;
wDayOfWeek: Word;
wDay: Word;
wHour: Word;
wMinute: Word;
wSecond: Word;
wMilliseconds: Word;
end;
{$EXTERNALSYM _SYSTEMTIME}
TSystemTime = _SYSTEMTIME;
SYSTEMTIME = _SYSTEMTIME;
{$EXTERNALSYM SYSTEMTIME}