Java 获取系统时间

1. Date类

Date day=new Date();
SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
System.out.println(df.format(day));
// 或者 
Date date = new Date();    
String year = String.format("%tY", date);
String month = String.format("%tB", date);
String day = String.format("%te", date);
System.out.println(year+"-"+month+"-"+day);

2. System类

SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
System.out.println(df.format(System.currentTimeMillis()));

3. Calendar类

Calendar c = Calendar.getInstance();//可以对每个时间域单独修改
int year = c.get(Calendar.YEAR);
int month = c.get(Calendar.MONTH);
int date = c.get(Calendar.DATE);
int hour = c.get(Calendar.HOUR_OF_DAY);
int minute = c.get(Calendar.MINUTE);
int second = c.get(Calendar.SECOND);
System.out.println(year + "-" + month + "-" + date + " " +hour + ":" +minute + ":" + second);

 总结：系统时间可通过Date类、Calendar类和System中的currentTimeMillis来获取，时间格式可通过调用SimpleDateFormat类和String中的format方法来设置。