java 时间处理

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);