String s1 = "2019-01-06 :12:02:20";
String s2 = "2019-01-07 :12:02:20";
SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd");
int day =(int)((df.parse(s2).getTime()
- df.parse(s1).getTime()) / (24 * 60 * 60 * 1000));
System.out.println(day);
输出结果:1