Java取一年有多少周、某周的第一天和最后一天

 import java.text.SimpleDateFormat;

import java.util.Calendar;

import java.util.Date;

import java.util.GregorianCalendar;
public class WeekUtils {

 // 获取当前时间所在年的周数

 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);

 }

 // 获取当前时间所在年的最大周数

 public static int getMaxWeekNumOfYear(int year) {

  Calendar c = new GregorianCalendar();

  c.set(year, Calendar.DECEMBER, 31, 23, 59, 59);

  return getWeekOfYear(c.getTime());

 }

 // 获取某年的第几周的开始日期

 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());

 }

 // 获取某年的第几周的结束日期

 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());

 }

 // 获取当前时间所在周的开始日期

 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();

 }

 // 获取当前时间所在周的结束日期

 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();

 }

 public static void main(String[] args) {

  int year = 2011;

  int week = 1;

  SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

  Date today = new Date();

  Calendar c = new GregorianCalendar();

  c.setTime(today);

  System.out.println("current date = " + sdf.format(today));

  System.out.println("getWeekOfYear = " + getWeekOfYear(today));

  System.out.println("getMaxWeekNumOfYear = " + getMaxWeekNumOfYear(year));

  System.out.println("getFirstDayOfWeek = " + sdf.format(getFirstDayOfWeek(year, week)));

  System.out.println("getLastDayOfWeek = " + sdf.format(getLastDayOfWeek(year, week)));

  System.out.println("getFirstDayOfWeek = " + sdf.format(getFirstDayOfWeek(today)));

  System.out.println("getLastDayOfWeek = " + sdf.format(getLastDayOfWeek(today)));

 }

}