关于时间的处理

//【java】String转Date与Date转String

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

//【java】判断今天是星期几

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

//【java】判断两个时间的大小

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

SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");           
Date d1 = sdf.parse("2018-06-01");           
Date d2 = sdf.parse("2018-06-02"); 
Date d3 = sdf.parse("2018-06-02"); 
System.out.println(d1.before(d2));//true d1<d2
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

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

 //【java】获取一个月有多少天（最大天数）

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
Calendar calendar = Calendar.getInstance();
calendar.setTime(sdf.parse("2020-01-3"));
int num = calendar.getActualMaximum(Calendar.DAY_OF_MONTH);
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

//【java】获取当前日期n天后的日期

Calendar calendar2 = Calendar.getInstance();
SimpleDateFormat sdf2 = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
calendar2.add(Calendar.DATE, 3);
String daysDelay = sdf2.format(calendar2.getTime());

//【java】获取当前时间

SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");//设置日期格式
String nowtime = df.format(new Date());

//【js】获取当前时间 年月日

var date = new Date();
var year = date.getFullYear();
var month = date.getMonth() + 1;
var day = date.getDate();
if (month < 10) {
    month = "0" + month;
}
if (day < 10) {
    day = "0" + day;
}
var nowDate = year + "-" + month + "-" + day;

持续更新！！