获取日期前一天，字符串转时间戳

//获取日期前一天

public static void main(String[] args) throws ParseException {
    SimpleDateFormat ss = new SimpleDateFormat("yyyy-MM-dd");
     String a = "2019-12-01";
     Date day= ss.parse(a);
     long ms = day.getTime() - 1*24*3600*1000L;
     Date prevDay = new Date(ms);
     String pre = ss.format(prevDay);
     System.out.println(pre);
 }

日期转当天时间段

public static void main(String[] args) {
    String time = "2019-12-01";

    String begin = time.replaceAll("-", "") + "000000";
    String end   = time.replaceAll("-", "") + "235959";
    System.out.println("begin:"+begin);
    System.out.println("end:"+end);
    }

//时间转时间戳

public static void main(String[] args) throws ParseException {  
        String a = "2019-12-03";
        String b = a+" 00:00:00";
        System.out.println(b);
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        long tt = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").parse(b).getTime()/1000;
        System.out.println(tt);
    }