Java如何获得系统时间

import java.text.DateFormat;

import java.text.ParsePosition;

import java.text.SimpleDateFormat;

import java.util.Calendar;

import java.util.Date;

import java.util.GregorianCalendar;

public class TimeTest {

//用来全局控制 上一周，本周，下一周的周数变化

private  int weeks = 0;

private int MaxDate;//一月最大天数

private int MaxYear;//一年最大天数

public static void main(String[] args) {

TimeTest tt = new TimeTest();

System.out.println("获取当天日期:"+tt.getNowTime("yyyy-MM-dd"));

System.out.println("获取本周一日期:"+tt.getMondayOFWeek());

System.out.println("获取本周日的日期~:"+tt.getCurrentWeekday());

System.out.println("获取上周一日期:"+tt.getPreviousWeekday());

System.out.println("获取上周日日期:"+tt.getPreviousWeekSunday());

System.out.println("获取下周一日期:"+tt.getNextMonday());

System.out.println("获取下周日日期:"+tt.getNextSunday());

System.out.println("获得相应周的周六的日期:"+tt.getNowTime("yyyy-MM-dd"));

System.out.println("获取本月第一天日期:"+tt.getFirstDayOfMonth());

System.out.println("获取本月最后一天日期:"+tt.getDefaultDay());

System.out.println("获取上月第一天日期:"+tt.getPreviousMonthFirst());

System.out.println("获取上月最后一天的日期:"+tt.getPreviousMonthEnd());

System.out.println("获取下月第一天日期:"+tt.getNextMonthFirst());

System.out.println("获取下月最后一天日期:"+tt.getNextMonthEnd());

System.out.println("获取本年的第一天日期:"+tt.getCurrentYearFirst());

System.out.println("获取本年最后一天日期:"+tt.getCurrentYearEnd());

System.out.println("获取去年的第一天日期:"+tt.getPreviousYearFirst());

System.out.println("获取去年的最后一天日期:"+tt.getPreviousYearEnd());

System.out.println("获取明年第一天日期:"+tt.getNextYearFirst());

System.out.println("获取明年最后一天日期:"+tt.getNextYearEnd());

System.out.println("获取本季度第一天到最后一天:"+tt.getThisSeasonTime(11));

System.out.println("获取两个日期之间间隔天数2008-12-1~2008-9.29:"+TimeTest.getTwoDay("2008-12-1","2008-9-29"));

}

public static String getTwoDay(String sj1, String sj2) {

SimpleDateFormat myFormatter = new SimpleDateFormat("yyyy-MM-dd");

long day = 0;

try {

java.util.Date date = myFormatter.parse(sj1);

java.util.Date mydate = myFormatter.parse(sj2);

day = (date.getTime() - mydate.getTime()) / (24 * 60 * 60 * 1000);

} catch (Exception e) {

return "";

}

return day + "";

}

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());

}

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;

}

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;

}

// 计算当月最后一天,返回字符串

public String getDefaultDay(){

String str = "";

SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");

Calendar lastDate = Calendar.getInstance();

lastDate.set(Calendar.DATE,1);//设为当前月的1号

lastDate.add(Calendar.MONTH,1);//加一个月，变为下月的1号

lastDate.add(Calendar.DATE,-1);//减去一天，变为当月最后一天

str=sdf.format(lastDate.getTime());

return str;

}

// 上月第一天

public String getPreviousMonthFirst(){

String str = "";

SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");

Calendar lastDate = Calendar.getInstance();

lastDate.set(Calendar.DATE,1);//设为当前月的1号

lastDate.add(Calendar.MONTH,-1);//减一个月，变为下月的1号

//lastDate.add(Calendar.DATE,-1);//减去一天，变为当月最后一天

str=sdf.format(lastDate.getTime());

return str;

}

//获取当月第一天

public String getFirstDayOfMonth(){

String str = "";

SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");

Calendar lastDate = Calendar.getInstance();

lastDate.set(Calendar.DATE,1);//设为当前月的1号

str=sdf.format(lastDate.getTime());

return str;

}

// 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;

}

public String getNowTime(String dateformat){

Date   now   =   new   Date();

SimpleDateFormat   dateFormat   =   new   SimpleDateFormat(dateformat);//可以方便地修改日期格式

String  hehe  = dateFormat.format(now);

return hehe;

}

// 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;

}

}

//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;

}

//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;

}