Java中用Calendar類計算周和周的起始日期(轉)

package com.tongyue.hot.web;

import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;

public class Dateutil {

 /**
 * 取得當前日期是多少周
 *
 * @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);
 }

 /**
 * 得到某一年周的總數
 *
 * @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 ());
 }

 /**
 * 得到某年某周的最後一天
 *
 * @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後一天
 *
 * @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();
 }
 
 /**
 * 取得當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 ();
 }

 /**
 * 取得當前日期所在周的最後一天
 *
 * @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());
  }
 */
}