Java中对日期的常用处理

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

/** *//**
 * 
 * @author zzk
 *
 */
public class DateUtil {

    /** *//**
     * 取得某天相加(减)後的那一天
     * 
     * @param date
     * @param num(可正可负)
     * @return
     */
    public static Date getAnotherDate(Date date, int num) {
        Calendar c = Calendar.getInstance();
        c.setTime(date);
        c.add(Calendar.DAY_OF_YEAR, num);
        return c.getTime();
    }

    /** *//**
     * 取得某月的的最后一天
     * 
     * @param year
     * @param month
     * @return
     */
    public static Date getLastDayOfMonth(int year, int month) {
		Calendar cal = Calendar.getInstance();
		cal.set(Calendar.YEAR, year);// 年
		cal.set(Calendar.MONTH, month - 1);// 月，因为Calendar里的月是从0开始，所以要减1
		//设置该月实际的最后一天
		cal.set(Calendar.DATE,cal.getActualMaximum(Calendar.DATE));
		return cal.getTime();// 获得月末是几号 
    }
 
     /** *//**
      * 取得某天是一年中的多少周
     * 
     * @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);
    }

    /** *//**
     * 取得某天所在周的第一天
     * 
     * @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());
        return c.getTime();
    }

    /** *//**
     * 取得某天所在周的最后一天
     * 
     * @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);
        return c.getTime();
    }

    /** *//**
     * 取得某一年共有多少周
     * 
     * @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());
    }
    
    /** *//**
     * 取得某年某周的第一天
     * 对于交叉:2008-12-29到2009-01-04属于2008年的最后一周,2009-01-05为2009年第一周的第一天
     * @param year
     * @param week
     * @return
     */
    public static Date getFirstDayOfWeek(int year, int week) {
        Calendar calFirst = Calendar.getInstance();
        calFirst.set(year, 0, 7);
        Date firstDate = getFirstDayOfWeek(calFirst.getTime());

        Calendar firstDateCal = Calendar.getInstance();
        firstDateCal.setTime(firstDate);

        Calendar c = new GregorianCalendar();
        c.set(Calendar.YEAR, year);
        c.set(Calendar.MONTH, Calendar.JANUARY);
        c.set(Calendar.DATE, firstDateCal.get(Calendar.DATE));

        Calendar cal = (GregorianCalendar) c.clone();
        cal.add(Calendar.DATE, (week - 1) * 7);
        firstDate = getFirstDayOfWeek(cal.getTime());

        return firstDate;
    }

    /** *//**
     * 取得某年某周的最后一天
     * 对于交叉:2008-12-29到2009-01-04属于2008年的最后一周,2009-01-04为2008年最后一周的最后一天
     * @param year
     * @param week
     * @return
     */
    public static Date getLastDayOfWeek(int year, int week) {
        Calendar calLast = Calendar.getInstance();
        calLast.set(year, 0, 7);
        Date firstDate = getLastDayOfWeek(calLast.getTime());

        Calendar firstDateCal = Calendar.getInstance();
       firstDateCal.setTime(firstDate);

        Calendar c = new GregorianCalendar();
        c.set(Calendar.YEAR, year);
        c.set(Calendar.MONTH, Calendar.JANUARY);
        c.set(Calendar.DATE, firstDateCal.get(Calendar.DATE));

        Calendar cal = (GregorianCalendar) c.clone();
        cal.add(Calendar.DATE, (week - 1) * 7);
        Date lastDate = getLastDayOfWeek(cal.getTime());
        
        return lastDate;
    }
}