1.计算某一月份的最大天数
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Calendar time=Calendar.getInstance();
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time.clear();
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time.set(Calendar.YEAR,year); //year 为 int
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time.set(Calendar.MONTH,i-1);//注意,Calendar对象默认一月为0
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int day=time.getActualMaximum(Calendar.DAY_OF_MONTH);//本月份的天数
注:在使用set方法之前,必须先clear一下,否则很多信息会继承自系统当前时间
2.Calendar和Date的转化
(1) Calendar转化为Date
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Calendar cal=Calendar.getInstance();
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Date date=cal.getTime();
(2) Date转化为Calendar
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Date date=new Date();
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Calendar cal=Calendar.getInstance();
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cal.setTime(date);
3.格式化输出日期时间 (这个用的比较多)
其一
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Date date=new Date();
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SimpleDateFormat df=new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
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String time=df.format(date);
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System.out.println(time);//2008-10-27 08:52:32
其二
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Calendar c = Calendar.getInstance();
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System.out.println(c.getTime());//Mon Oct 27 08:51:21 CST 2008
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SimpleDateFormat simpleDateTimeFormat = new SimpleDateFormat(" yyyy-MM-dd HH:mm:ss ");
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c = Calendar.getInstance(Locale.CHINESE);
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System.out.println(simpleDateTimeFormat.format(c.getTime()));// 2008-10-27 08:51:21
4.计算一年中的第几星期
(1)计算某一天是一年中的第几星期
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Calendar cal=Calendar.getInstance();
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cal.set(Calendar.YEAR, 2006);
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cal.set(Calendar.MONTH, 8);
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cal.set(Calendar.DAY_OF_MONTH, 3);
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int weekno=cal.get(Calendar.WEEK_OF_YEAR);
(2)计算一年中的第几星期是几号
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SimpleDateFormat df=new SimpleDateFormat("yyyy-MM-dd");
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Calendar cal=Calendar.getInstance();
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cal.set(Calendar.YEAR, 2006);
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cal.set(Calendar.WEEK_OF_YEAR, 1);
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cal.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
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System.out.println(df.format(cal.getTime()));
输出:
2006-01-02
5.add()和roll()的用法(不太常用)
(1)add()方法
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SimpleDateFormat df=new SimpleDateFormat("yyyy-MM-dd");
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Calendar cal=Calendar.getInstance();
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cal.set(Calendar.YEAR, 2006);
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cal.set(Calendar.MONTH, 8);
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cal.set(Calendar.DAY_OF_MONTH, 3);
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cal.add(Calendar.DATE, -4);
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Date date=cal.getTime();
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System.out.println(df.format(date));
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cal.add(Calendar.DATE, 4);
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date=cal.getTime();
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System.out.println(df.format(date));
输出:
2006-08-30
2006-09-03
(2)roll方法
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cal.set(Calendar.YEAR, 2006);
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cal.set(Calendar.MONTH, 8);
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cal.set(Calendar.DAY_OF_MONTH, 3);
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cal.roll(Calendar.DATE, -4);
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date=cal.getTime();
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System.out.println(df.format(date));
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cal.roll(Calendar.DATE, 4);
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date=cal.getTime();
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System.out.println(df.format(date));
输出:
2006-09-29
2006-09-03
可见,roll()方法在本月内循环,一般使用add()方法;
6.计算两个任意时间中间的间隔天数(这个比较常用)
(1)传进Calendar对象
(2)传进Date对象
(3)改进精确计算相隔天数的方法
注意:通过上面的方法可以衍生出求任何时间,如要查出邮箱三周之内收到的邮件(得到当前系统时间-再得到三周前时间)用收件的时间去匹配 最好装化成 long去比较
如:1年前日期(注意毫秒的转换)
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java.util.Date myDate=new java.util.Date();
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long myTime=(myDate.getTime()/1000)-60*60*24*365;
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myDate.setTime(myTime*1000);
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String mDate=formatter.format(myDate);
7. String 和 Date ,Long 之间相互转换 (最常用)
字符串转化成时间类型(字符串可以是任意类型,只要和SimpleDateFormat中的格式一致即可)
通常我们取时间跨度的时候,会substring出具体时间--long-比较
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java.text.SimpleDateFormat sdf = new java.text.SimpleDateFormat("M/dd/yyyy hh:mm:ss a",java.util.Locale.US);
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java.util.Date d = sdf.parse("5/13/2003 10:31:37 AM");
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long dvalue=d.getTime();
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SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
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String mDateTime1=formatter.format(d);
8. 通过时间求时间
年月周求日期
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SimpleDateFormat formatter2 = new SimpleDateFormat("yyyy-MM F E");
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java.util.Date date2= formatter2.parse("2003-05 5 星期五");
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SimpleDateFormat formatter3 = new SimpleDateFormat("yyyy-MM-dd");
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String mydate2=formatter3.format(date2);
求是星期几
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mydate= myFormatter.parse("2001-1-1");
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SimpleDateFormat formatter4 = new SimpleDateFormat("E");
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String mydate3=formatter4.format(mydate);
9. java 和 具体的数据库结合
在开发web应用中,针对不同的数据库日期类型,我们需要在我们的程序中对日期类型做各种不同的转换。若对应数据库数据是oracle的Date类型,即只需要年月日的,可以选择使用java.sql.Date类型,若对应的是MSsqlserver 数据库的DateTime类型,即需要年月日时分秒的,选择java.sql.Timestamp类型
你可以使用dateFormat定义时间日期的格式,转一个字符串即可
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class Datetest
{
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*method 将字符串类型的日期转换为一个timestamp(时间戳记java.sql.Timestamp)
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*@param dateString 需要转换为timestamp的字符串
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*@return dataTime timestamp
5![](http://www.blogjava.net/Images/OutliningIndicators/InBlock.gif)
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public final static java.sql.Timestamp string2Time(String dateString)
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throws java.text.ParseException {
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DateFormat dateFormat;
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dateFormat = new SimpleDateFormat("yyyy-MM-dd kk:mm:ss.SSS", Locale.ENGLISH);//设定格式
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//dateFormat = new SimpleDateFormat("yyyy-MM-dd kk:mm:ss", Locale.ENGLISH);
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dateFormat.setLenient(false);
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java.util.Date timeDate = dateFormat.parse(dateString);//util类型
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java.sql.Timestamp dateTime = new java.sql.Timestamp(timeDate.getTime());//Timestamp类型,timeDate.getTime()返回一个long型
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return dateTime;
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}
16![](http://www.blogjava.net/Images/OutliningIndicators/InBlock.gif)
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*method 将字符串类型的日期转换为一个Date(java.sql.Date)
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*@param dateString 需要转换为Date的字符串
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*@return dataTime Date
20![](http://www.blogjava.net/Images/OutliningIndicators/InBlock.gif)
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public final static java.sql.Date string2Date(String dateString)
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throws java.lang.Exception {
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DateFormat dateFormat;
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dateFormat = new SimpleDateFormat("yyyy-MM-dd", Locale.ENGLISH);
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dateFormat.setLenient(false);
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java.util.Date timeDate = dateFormat.parse(dateString);//util类型
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java.sql.Date dateTime = new java.sql.Date(timeDate.getTime());//sql类型
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return dateTime;
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}
30![](http://www.blogjava.net/Images/OutliningIndicators/InBlock.gif)
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public static void main(String[] args){
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Date da = new Date();
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注意:这个地方da.getTime()得到的是一个long型的值
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System.out.println(da.getTime());
35![](http://www.blogjava.net/Images/OutliningIndicators/InBlock.gif)
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由日期date转换为timestamp
37![](http://www.blogjava.net/Images/OutliningIndicators/InBlock.gif)
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第一种方法:使用new Timestamp(long)
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Timestamp t = new Timestamp(new Date().getTime());
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System.out.println(t);
41![](http://www.blogjava.net/Images/OutliningIndicators/InBlock.gif)
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第二种方法:使用Timestamp(int year,int month,int date,int hour,int minute,int second,int nano)
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Timestamp tt = new Timestamp(Calendar.getInstance().get(
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Calendar.YEAR) - 1900, Calendar.getInstance().get(
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Calendar.MONTH), Calendar.getInstance().get(
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Calendar.DATE), Calendar.getInstance().get(
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Calendar.HOUR), Calendar.getInstance().get(
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Calendar.MINUTE), Calendar.getInstance().get(
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Calendar.SECOND), 0);
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System.out.println(tt);
51![](http://www.blogjava.net/Images/OutliningIndicators/InBlock.gif)
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try {
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String sToDate = "2005-8-18";//用于转换成java.sql.Date的字符串
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String sToTimestamp = "2005-8-18 14:21:12.123";//用于转换成java.sql.Timestamp的字符串
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Date date1 = string2Date(sToDate);
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Timestamp date2 = string2Time(sToTimestamp);
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System.out.println("Date:"+date1.toString());//结果显示
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System.out.println("Timestamp:"+date2.toString());//结果显示
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}catch(Exception e) {
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e.printStackTrace();
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}
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}
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}
64![](http://www.blogjava.net/Images/OutliningIndicators/None.gif)