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))); }}