java常用的日期函数介绍(1/2)
Java统计从1970年1月1日起的毫秒的数量表示日期。也就是说,例如,1970年1月2日,是在1月1日后的86,400,000毫秒。同样的,1969年12月31日是在1970年1月1日前86,400,000毫秒
1)String类型转换成日期(Date类型):
SimpleDateFormat myFormatter = new SimpleDateFormat("yyyy-MM-dd");
java.util.Date date = myFormatter.parse(sj1);
java.util.Date mydate = myFormatter.parse(sj2);
(2) 根据一个日期,返回是星期几的字符串
public static String getWeek(String sdate) {
// 再转换为时间
Date date = TimeTest.strToDate(sdate);
Calendar c = Calendar.getInstance();
c.setTime(date);
// int hour=c.get(Calendar.DAY_OF_WEEK);
// hour中存的就是星期几了,其范围 1~7
// 1=星期日 7=星期六,其他类推
return new SimpleDateFormat("EEEE").format(c.getTime());
}
(3) 将短时间格式字符串转换为时间 yyyy-MM-dd
public static Date strToDate(String strDate) {
SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd");
ParsePosition pos = new ParsePosition(0);
Date strtodate = formatter.parse(strDate, pos);
return strtodate;
}
(4) 两个时间之间的天数之差
public static long getDays(String date1, String date2) {
if (date1 == null || date1.equals(""))
return 0;
if (date2 == null || date2.equals(""))
return 0;
// 转换为标准时间
SimpleDateFormat myFormatter = new SimpleDateFormat("yyyy-MM-dd");
java.util.Date date = null;
java.util.Date mydate = null;
try {
date = myFormatter.parse(date1);
mydate = myFormatter.parse(date2);
} catch (Exception e) {
}
long day = (date.getTime() - mydate.getTime()) / (24 * 60 * 60 * 1000);
return day;
}
(5) 获得本周星期日的日期
public String getCurrentWeekday() {
weeks = 0;
int mondayPlus = this.getMondayPlus();
GregorianCalendar currentDate = new GregorianCalendar();
currentDate.add(GregorianCalendar.DATE, mondayPlus+6);
Date monday = currentDate.getTime();
DateFormat df = DateFormat.getDateInstance();
String preMonday = df.format(monday);
return preMonday;
}
(6)获取当天时间
Date now = new Date();
上面基于date函数的
Date类可以在java.util包中找到,用一个long类型的值表示一个指定的时刻。它的一个有用的构造函数是Date(),它创建一个表示创建时刻的对象。getTime()方法返回Date对象的long值。在下面的程序中,我使用Date()构造函数创建一个表示程序运行时刻的对象,并且利用getTime()方法找到这个日期代表的毫秒数量:
(7) 获得当前日期与本周日相差的天数
private int getMondayPlus() {
Calendar cd = Calendar.getInstance();
// 获得今天是一周的第几天,星期日是第一天,星期二是第二天......
int dayOfWeek = cd.get(Calendar.DAY_OF_WEEK)-1; //因为按中国礼拜一作为第一天所以这里减1
if (dayOfWeek == 1) {
return 0;
} else {
return 1 - dayOfWeek;
}
}
(8)获得本周一的日期
public String getMondayOFWeek(){
weeks = 0;
int mondayPlus = this.getMondayPlus();
GregorianCalendar currentDate = new GregorianCalendar();
currentDate.add(GregorianCalendar.DATE, mondayPlus);
Date monday = currentDate.getTime();
DateFormat df = DateFormat.getDateInstance();
String preMonday = df.format(monday);
return preMonday;
}
(9)获得相应周的周六的日期
public String getSaturday() {
int mondayPlus = this.getMondayPlus();
GregorianCalendar currentDate = new GregorianCalendar();
currentDate.add(GregorianCalendar.DATE, mondayPlus + 7 * weeks + 6);
Date monday = currentDate.getTime();
DateFormat df = DateFormat.getDateInstance();
String preMonday = df.format(monday);
return preMonday;
}
(10) 获得上周星期日的日期
public String getPreviousWeekSunday() {
weeks=0;
weeks--;
int mondayPlus = this.getMondayPlus();
GregorianCalendar currentDate = new GregorianCalendar();
currentDate.add(GregorianCalendar.DATE, mondayPlus+weeks);
Date monday = currentDate.getTime();
DateFormat df = DateFormat.getDateInstance();
String preMonday = df.format(monday);
return preMonday;
}
(11)获得上周星期一的日期
public String getPreviousWeekday() {
weeks--;
int mondayPlus = this.getMondayPlus();
GregorianCalendar currentDate = new GregorianCalendar();
currentDate.add(GregorianCalendar.DATE, mondayPlus + 7 * weeks);
Date monday = currentDate.getTime();
DateFormat df = DateFormat.getDateInstance();
String preMonday = df.format(monday);
return preMonday;
}
(12) 获得下周星期一的日期
public String getNextMonday() {
weeks++;
int mondayPlus = this.getMondayPlus();
GregorianCalendar currentDate = new GregorianCalendar();
currentDate.add(GregorianCalendar.DATE, mondayPlus + 7);
Date monday = currentDate.getTime();
DateFormat df = DateFormat.getDateInstance();
String preMonday = df.format(monday);
return preMonday;
}
(13)获得下周星期日的日期
public String getNextSunday() {
int mondayPlus = this.getMondayPlus();
GregorianCalendar currentDate = new GregorianCalendar();
currentDate.add(GregorianCalendar.DATE, mondayPlus + 7+6);
Date monday = currentDate.getTime();
DateFormat df = DateFormat.getDateInstance();
String preMonday = df.format(monday);
return preMonday;
}
(14)获得上月最后一天的日期
public String getPreviousMonthEnd(){
String str = "";
SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");
Calendar lastDate = Calendar.getInstance();
lastDate.add(Calendar.MONTH,-1);//减一个月
lastDate.set(Calendar.DATE, 1);//把日期设置为当月第一天
lastDate.roll(Calendar.DATE, -1);//日期回滚一天,也就是本月最后一天
str=sdf.format(lastDate.getTime());
return str;
}
(15)获得下个月第一天的日期
public String getNextMonthFirst(){
String str = "";
SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");
Calendar lastDate = Calendar.getInstance();
lastDate.add(Calendar.MONTH,1);//减一个月
lastDate.set(Calendar.DATE, 1);//把日期设置为当月第一天
str=sdf.format(lastDate.getTime());
return str;
}
(16)获得下个月最后一天的日期
public String getNextMonthEnd(){
String str = "";
SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");
Calendar lastDate = Calendar.getInstance();
lastDate.add(Calendar.MONTH,1);//加一个月
lastDate.set(Calendar.DATE, 1);//把日期设置为当月第一天
lastDate.roll(Calendar.DATE, -1);//日期回滚一天,也就是本月最后一天
str=sdf.format(lastDate.getTime());
return str;
}
(17)获得明年最后一天的日期
public String getNextYearEnd(){
String str = "";
SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");
Calendar lastDate = Calendar.getInstance();
lastDate.add(Calendar.YEAR,1);//加一个年
lastDate.set(Calendar.DAY_OF_YEAR, 1);
lastDate.roll(Calendar.DAY_OF_YEAR, -1);
str=sdf.format(lastDate.getTime());
return str;
}
(18)获得明年第一天的日期
public String getNextYearFirst(){
String str = "";
SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");
Calendar lastDate = Calendar.getInstance();
lastDate.add(Calendar.YEAR,1);//加一个年
lastDate.set(Calendar.DAY_OF_YEAR, 1);
str=sdf.format(lastDate.getTime());
return str;
}
(19)获得本年有多少天
private int getMaxYear(){
Calendar cd = Calendar.getInstance();
cd.set(Calendar.DAY_OF_YEAR,1);//把日期设为当年第一天
cd.roll(Calendar.DAY_OF_YEAR,-1);//把日期回滚一天。
int MaxYear = cd.get(Calendar.DAY_OF_YEAR);
return MaxYear;
}
}
(20)获得本年第一天的日期
public String getCurrentYearFirst(){
int yearPlus = this.getYearPlus();
GregorianCalendar currentDate = new GregorianCalendar();
currentDate.add(GregorianCalendar.DATE,yearPlus);
Date yearDay = currentDate.getTime();
DateFormat df = DateFormat.getDateInstance();
String preYearDay = df.format(yearDay);
return preYearDay;
}
(21)获得本年最后一天的日期 *
public String getCurrentYearEnd(){
Date date = new Date();
SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy");//可以方便地修改日期格式
String years = dateFormat.format(date);
return years+"-12-31";
}
补充:Jsp教程,Java基础