JodaTime supports parsing from a user-defined format. See DateTimeFormatterBuilder and DateTimeBuilder.parseDateTime().
Once you have a DateTime, you can create a Duration or Period from that and the current time, and use another formatter to pretty-print. [See the PeriodFormatter example referenced by BalusC in comments above.]
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…