用joda datetime的days.between即可。
DateTime dt1 = new DateTime(d1);
DateTime dt2 = new DateTime(d2);
System.out.print("两个时间相差:");
System.out.print(Days.daysBetween(dt1, dt2).getDays() + " 天, ");
refurl:http://www.blogjava.net/qiyadeng/archive/2013/02/19/395428.html
http://wandejun1012.iteye.com/admin/blogs/1746662