JAVA中用CALENDAR类计算周和周的起始日期(转)

public class Dateutil {

?/**?
?* 取得当前日期是多少周?
?*?
?* @param date?
?* @return?
?*/?
?public static int getWeekOfYear(Date date) {?
?Calendar c = new GregorianCalendar();?
?c.setFirstDayOfWeek(Calendar.MONDAY);?
?c.setMinimalDaysInFirstWeek(7);?
?c.setTime (date);

?return c.get(Calendar.WEEK_OF_YEAR);?
?}

?/**?
?* 得到某一年周的总数?
?*?
?* @param year?
?* @return?
?*/?
?public static int getMaxWeekNumOfYear(int year) {?
?Calendar c = new GregorianCalendar();?
?c.set(year, Calendar.DECEMBER, 31, 23, 59, 59);

?return getWeekOfYear(c.getTime());?
?}

?/**?
?* 得到某年某周的第一天?
?*?
?* @param year?
?* @param week?
?* @return?
?*/?
?public static Date getFirstDayOfWeek(int year, int week) {?
?Calendar c = new GregorianCalendar();?
?c.set(Calendar.YEAR, year);?
?c.set (Calendar.MONTH, Calendar.JANUARY);?
?c.set(Calendar.DATE, 1);

?Calendar cal = (GregorianCalendar) c.clone();?
?cal.add(Calendar.DATE, week * 7);

?return getFirstDayOfWeek(cal.getTime ());?
?}

?/**?
?* 得到某年某周的最后一天?
?*?
?* @param year?
?* @param week?
?* @return?
?*/?
?public static Date getLastDayOfWeek(int year, int week) {?
?Calendar c = new GregorianCalendar();?
?c.set(Calendar.YEAR, year);?
?c.set(Calendar.MONTH, Calendar.JANUARY);?
?c.set(Calendar.DATE, 1);

?Calendar cal = (GregorianCalendar) c.clone();?
?cal.add(Calendar.DATE , week * 7);

?return getLastDayOfWeek(cal.getTime());?
?}

?/**?
?* 取得指定日期所在周的第一天?
?*?
?* @param date?
?* @return?
?*/?
?public static Date getFirstDayOfWeek(Date date) {?
?Calendar c = new GregorianCalendar();?
?c.setFirstDayOfWeek(Calendar.MONDAY);?
?c.setTime(date);?
?c.set(Calendar.DAY_OF_WEEK, c.getFirstDayOfWeek()); // Monday?
?return c.getTime ();?
?}

?/**?
?* 取得指定日期所在周的最后一天?
?*?
?* @param date?
?* @return?
?*/?
?public static Date getLastDayOfWeek(Date date) {?
?Calendar c = new GregorianCalendar();?
?c.setFirstDayOfWeek(Calendar.MONDAY);?
?c.setTime(date);?
?c.set(Calendar.DAY_OF_WEEK, c.getFirstDayOfWeek() + 6); // Sunday?
?return c.getTime();?
?}?
?
?/**?
?* 取得当前日期所在周的第一天?
?*?
?* @param date?
?* @return?
?*/?
?public static Date getFirstDayOfWeek() {?
?Calendar c = new GregorianCalendar();?
?c.setFirstDayOfWeek(Calendar.MONDAY);?
?c.setTime(new Date());?
?c.set(Calendar.DAY_OF_WEEK, c.getFirstDayOfWeek()); // Monday?
?return c.getTime ();?
?}

?/**?
?* 取得当前日期所在周的最后一天?
?*?
?* @param date?
?* @return?
?*/?
?public static Date getLastDayOfWeek() {?
?Calendar c = new GregorianCalendar();?
?c.setFirstDayOfWeek(Calendar.MONDAY);?
?c.setTime(new Date());?
?c.set(Calendar.DAY_OF_WEEK, c.getFirstDayOfWeek() + 6); // Sunday?
?return c.getTime();?
?}?
?/*
? *?
??
?public static void main(String[] args) {?
??int year = 2009;?
??int week = 1;

??// 以2006-01-02位例?
??Calendar c = new GregorianCalendar();?
??c.set(2009, Calendar.DECEMBER, 7);?
??Date d = c.getTime();

??System.out.println("current date = " + d);?
??System.out.println("getWeekOfYear = " + getWeekOfYear(d));?
??System.out.println("getMaxWeekNumOfYear = " + getMaxWeekNumOfYear(year));?
??System.out.println("getFirstDayOfWeek = " + getFirstDayOfWeek(year, week));?
??System.out.println("getLastDayOfWeek = " + getLastDayOfWeek(year, week));?
??System.out.println ("getFirstDayOfWeek = " + getFirstDayOfWeek(d));?
??System.out.println("getLastDayOfWeek = " + getLastDayOfWeek(d));?
??System.out.println ("getFirstDayOfWeek = " + getFirstDayOfWeek());?
??System.out.println("getLastDayOfWeek = " + getLastDayOfWeek());?
??}
?*/?
}