The current FTPFileObject implementation delegates to the commons-net FtpFile to get the last modified date. Unfortunately this value is parsed from the result of the LIST command, which suffers from a few issues:
NET-212- LMDs aren't persistable beyond a year as commons-net has to guess the year in many cases, based on the current year.
- Most FTP parser formats are only accurate to the minute, and sometimes only the nearest day
- Sometimes the FTP server will change the time format for a single file over time, changing the resulting lmd.
By using the MDTM command you're able to get a last modified date that's accurate to the second (and sometimes even millisecond) and doesn't suffer from the above issues. As I understand it, the command is implemented in commons-net 2.1?