获取当前时间的相关信息
Calendar now = Calendar.getInstance();
System.out.println("年: " + now.get(Calendar.YEAR));
System.out.println("月: " + (now.get(Calendar.MONTH) + 1) + "");
System.out.println("日: " + now.get(Calendar.DAY_OF_MONTH));
System.out.println("时: " + now.get(Calendar.HOUR_OF_DAY));
System.out.println("分: " + now.get(Calendar.MINUTE));
System.out.println("秒: " + now.get(Calendar.SECOND));
System.out.println("当前时间毫秒数：" + now.getTimeInMillis());
System.out.println(now.getTime());
Date d = new Date();
System.out.println(d);
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
String dateNowStr = sdf.format(d);
System.out.println("格式化后的日期：" + dateNowStr);
String str = "2012-1-13 17:26:33"; //要跟上面sdf定义的格式一样
Date today = sdf.parse(str);
System.out.println("字符串转成日期：" + today);
结果：
年: 2020
月: 4
日: 17
时: 11
分: 28
秒: 19
当前时间毫秒数：1587093559000
Fri Apr 17 11:28:19 CST 2020
Fri Apr 17 11:28:19 CST 2020
格式化后的日期：2020-04-17 17:28:19
字符串转成日期：Fri Apr 17 17:26:33 CST 2020
