Java中用Calendar类计算周和周的起始日期

package com.itywweeksoft.ambow.common;

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

/**
* Title: 周计算类，星期日为一周的开始，星期六为一周的结束
* Description: 在两年的交接地带还有疑问。
* 比如2006-12-29到2009-01-04，属于2008年的最后一周，
* 2009-01-04位2009年第一周的开始。
*/
public class WeekUtil {
/**
* 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.SUNDAY);
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());
}

/**
* 取得当前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.SUNDAY);
c.setTime(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(Date date) {
Calendar c = new GregorianCalendar();
c.setFirstDayOfWeek(Calendar.SUNDAY);
c.setTime(date);
c.set(Calendar.DAY_OF_WEEK, c.getFirstDayOfWeek() + 6); // Sunday
return c.getTime();
}

/**
* 日期转换成字符串
* @param date  日期
* @param pattern 格式
* @return  转换后的字符串
*/
public static String defaultDateToStr(java.util.Date date, String pattern)
{
if( date == null ){
return "";
}
SimpleDateFormat ft = new SimpleDateFormat(pattern);
return ft.format(date);
}

public static void main(String[] args) {
int year = 2006;
int week = 1;

// 以2006-01-02位例
Calendar c = new GregorianCalendar();
c.set(2006, Calendar.JANUARY, 2);
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));
}
}