java 获取当前时间及类型转换

1.通过Util包中的Date获取

Date date = new Date();
SimpleDateFormat dateFormat= new SimpleDateFormat("yyyy-MM-dd :hh:mm:ss");
System.out.println(dateFormat.format(date));

2.通过Util包的Calendar 获取

Calendar calendar= Calendar.getInstance();
SimpleDateFormat dateFormat= new SimpleDateFormat("yyyy-MM-dd :hh:mm:ss");
System.out.println(dateFormat.format(calendar.getTime()));

3.通过Util包的Calendar 获取时间，分别获取年月日时分秒

Calendar cal=Calendar.getInstance();      
int y=cal.get(Calendar.YEAR);      
int m=cal.get(Calendar.MONTH);      
int d=cal.get(Calendar.DATE);      
int h=cal.get(Calendar.HOUR_OF_DAY);      
int mi=cal.get(Calendar.MINUTE);      
int s=cal.get(Calendar.SECOND);      
System.out.println("现在时刻是"+y+"年"+m+"月"+d+"日"+h+"时"+mi+"分"+s+"秒");

java中Date与String的相互转换

java中通过SimpleDateFormat的parse和format方法可以实现Date与String的相互转换

1.String转Date

String str1 = "2021-09-24 12:13:14";
SimpleDateFormat sdf1 = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
Date myDate1 = null;
try {
    myDate1 = sdf1.parse(str1);
}catch (Exception e){
    e.printStackTrace();
}
System.out.println("myDate1: "+myDate1);

2.Date转String

SimpleDateFormat sdf4 = new SimpleDateFormat("yyyy年MM月dd日 HH时mm分ss秒");
String strDate4 = sdf4.format(myDate);
System.out.println("strDate4:" + strDate4);