关于时间的处理

//【java】String转Date与Date转String

1 //String转Date
2 Date date = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").parse("2020-01-01 12:01:23");
3 System.out.println(date);//Wed Jan 01 12:01:23 CST 2020
4 //Date转String
5 String time = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date());
6 System.out.println(time);//2020-01-03 14:18:29

//【java】判断今天是星期几

1 String[] weekDays = { "星期日", "星期一", "星期二", "星期三", "星期四", "星期五", "星期六" };
2 Calendar cal = Calendar.getInstance();
3 cal.setTime(new Date());
4 int w = cal.get(Calendar.DAY_OF_WEEK) - 1;
5 if (w < 0)
6     w = 0;
7 String week = weekDays[w];
8 System.out.println(week);//不差天数

//【java】判断两个时间的大小

1 String a = "11:11:11";
2 String b = "12:11:11";
3 String s1 = "2019-02-01";
4 String s2 = "2019-02-02";
5 System.out.println(a.compareTo(b));//结果是 -1 a<b
6 System.out.println(s2.compareTo(s1));//结果是 1 s2>s1

1 SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");           
2 Date d1 = sdf.parse("2018-06-01");           
3 Date d2 = sdf.parse("2018-06-02"); 
4 Date d3 = sdf.parse("2018-06-02"); 
5 System.out.println(d1.before(d2));//true d1<d2
6 System.out.println(d2.before(d3));//false d2<d3 可以通过比较字符串是否相等来判断

//【java】两个时间相差的秒数

1 Date a = new Date(); 
2 Date b = new Date(); 
3 long second = (b.getTime() - a.getTime())/1000; 
4 System.out.println(second);//结果为0

//【java】获取一个月有多少天（最大天数）

1 SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
2 Calendar calendar = Calendar.getInstance();
3 calendar.setTime(sdf.parse("2020-01-3"));
4 int num = calendar.getActualMaximum(Calendar.DAY_OF_MONTH);
5 System.out.println(num);//结果为31

//【java】单独获取时分秒

Date d = new Date();
int hours = d.getHours();//时
int minutes = d.getMinutes();//分
int second = d.getSeconds();//秒

//【js】获取当前时间年月日

 1 var date = new Date();
 2 var year = date.getFullYear();
 3 var month = date.getMonth() + 1;
 4 var day = date.getDate();
 5 if (month < 10) {
 6     month = "0" + month;
 7 }
 8 if (day < 10) {
 9     day = "0" + day;
10 }
11 var nowDate = year + "-" + month + "-" + day;

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