java.util.Calendar
Calendar 类是一个抽象类，它为特定瞬间与一组诸如 YEAR、MONTH、DAY_OF_MONTH、HOUR 等 日历字段之间的转换提供了一些方法，并为操作日历字段（例如获得下星期的日期）提供了一些方法。瞬间可用毫秒值来表示，它是距历元（即格林威治标准时间 1970 年 1 月 1 日的 00:00:00.000，格里高利历）的偏移量。
简单示例
// 通过格式化输出日期
java.text.SimpleDateFormat format = new java.text.SimpleDateFormat("yyyy-MM-dd");
Calendar cal = Calendar.getInstance();// 取当前日期。
System.out.println("Today is:" + format.format(cal.getTime()));
cal = Calendar.getInstance();
cal.add(Calendar.DAY_OF_MONTH, -1);// 取当前日期的前一天.
System.out.println("yesterday is:" + format.format(cal.getTime()));
cal = Calendar.getInstance();
cal.add(Calendar.DAY_OF_MONTH, +1);// 取当前日期的后一天.
System.out.println("nextday is:" + format.format(cal.getTime()));
或者
java.util.Date today=new java.util.Date();
java.text.SimpleDateFormat dateFormat = new java.text.SimpleDateFormat("yyyy-MM-dd");
java.text.SimpleDateFormat dateTimeFormat = new java.text.SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
System.out.println("Today is "+dateFormat.format(today));
System.out.println("Now is "+dateTimeFormat.format(today));
构造特定时间
java.text.SimpleDateFormat format = new java.text.SimpleDateFormat("yyyy-MM-dd");
Calendar calendar = new GregorianCalendar(2007, 11, 25,0,0,0);
Date date = calendar.getTime();
System.out.println("2007 Christmas is:"+format.format(date));
GregorianCalendar构造方法参数依次为：年，月-1，日，时，分，秒.
或者
java.text.SimpleDateFormat format = new java.text.SimpleDateFormat("yyyy-MM-dd");
java.util.Date date= format.parse("2007-12-25");
System.out.println("2007 Christmas is:"+format.format(date));
取日期的每部分
int year =calendar.get(Calendar.YEAR);
int month=calendar.get(Calendar.MONTH)+1;
int day =calendar.get(Calendar.DAY_OF_MONTH);
int hour =calendar.get(Calendar.HOUR_OF_DAY);
int minute =calendar.get(Calendar.MINUTE);
int second =calendar.get(Calendar.SECOND);
取月份要加1
获取当前月份的最大天数
Calendar cal = Calendar.getInstance();
int day=cal.getActualMaximum(Calendar.DAY_OF_MONTH);
System.out.println(day);
取当月的最后一天
Calendar cal = Calendar.getInstance();
int maxDay=cals.getActualMaximum(Calendar.DAY_OF_MONTH);
java.text.Format formatter3=new java.text.SimpleDateFormat("yyyy-MM-"+maxDay);
System.out.println(formatter3.format(cal.getTime()));
取当月的第一天
java.text.SimpleDateFormat format = new java.text.SimpleDateFormat("yyyy-MM-01");
java.util.Date firstDay=new java.util.Date();
System.out.println("the month first day is "+formats.format(firstDay));
求两个日期之间相隔的天数
java.text.SimpleDateFormat format = new java.text.SimpleDateFormat("yyyy-MM-dd");
java.util.Date beginDate= format.parse("2007-12-24");
java.util.Date endDate= format.parse("2007-12-25");
long day=(date.getTime()-mydate.getTime())/(24*60*60*1000);
System.out.println("相隔的天数="+day);
一年前的日期
java.text.Format formatter=new java.text.SimpleDateFormat("yyyy-MM-dd");
java.util.Date todayDate=new java.util.Date();
long beforeTime=(todayDate.getTime()/1000)-60*60*24*365;
todayDate.setTime(beforeTime*1000);
String beforeDate=formatter.format(todayDate);
System.out.println(beforeDate);
一年后的日期
java.text.Format formatter=new java.text.SimpleDateFormat("yyyy-MM-dd");
java.util.Date todayDate=new java.util.Date();
long afterTime=(todayDate.getTime()/1000)+60*60*24*365;
todayDate.setTime(afterTime*1000);
String afterDate=formatter.format(todayDate);
System.out.println(afterDate);
10小时后的时间
java.util.Calendar Cal=java.util.Calendar.getInstance();
Cal.setTime(dateOper);
Cal.add(java.util.Calendar.HOUR_OF_DAY,10);
System.out.println("date:"+forma.format(Cal.getTime()));
10小时前的时间
java.util.Calendar Cal=java.util.Calendar.getInstance();
Cal.setTime(dateOper);
Cal.add(java.util.Calendar.HOUR_OF_DAY,-10);
System.out.println("date:"+forma.format(Cal.getTime()));
当前日期的星期一和星期天
SimpleDateFormat dateFormat = new SimpleDateFormat("yyyyMMdd");
GregorianCalendar cal = new GregorianCalendar();
int dayInWeek = cal.get(Calendar.DAY_OF_WEEK);
int offset = 0;
if (dayInWeek == 1) {
// 星期天
offset = 6;
} else {
// 星期一至星期六
offset = dayInWeek - 2;
}
cal.add(GregorianCalendar.DAY_OF_MONTH, -offset);
String sday = dateFormat.format(cal.getTime());
cal.add(GregorianCalendar.DAY_OF_MONTH, 6);
String eday = dateFormat.format(cal.getTime());
System.out.println("这个星期的星期一:" + sday);
System.out.println("这个星期的星期天:" + eday);
获取当前日期所在的星期属于今年的第几周
GregorianCalendar cal = new GregorianCalendar();
int weekOfYear = cal.get(Calendar.WEEK_OF_YEAR);
System.out.println("这个星期属于第几周:" + weekOfYear);