Java gets how many weeks in a year, the first and last day of a week, and the actual number of weeks in the current year

import java.text.SimpleDateFormat;

import java.util.Calendar;

import java.util.Date;

import java.util.GregorianCalendar;

public class DateTest {

// Get the week number of the year in which the current time is located

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);

}

// Get the maximum week number of the year in which the current time is located

public static int getMaxWeekNumOfYear(int year) {

Calendar c = new GregorianCalendar();

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

return getWeekOfYear(c.getTime());

}

// Get the start date of the week of a year

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)));

System.out.println("---------------------------------------------------");

/*下边是解决年初第一周的前几天有可能也属于上一年的最后的一周的后几天,导致当前时间获取得到的所在周数和实际不符的问题*/

//获取当前年已经过的周数

c.setFirstDayOfWeek(Calendar.MONDAY);

c.setMinimalDaysInFirstWeek(7);

c.setTime(today);

//获取当前年的当前月份

int month = c.get(Calendar.MONTH) + 1;

int year2 = c.get(Calendar.YEAR);

int weekofYear1 = c.get(Calendar.WEEK_OF_YEAR);

System.out.println(weekofYear1);

String yearStr = String.valueOf(year2);

int yearint = Integer.parseInt(yearStr.substring(yearStr.length() - 1, yearStr.length()));

System.out.println(yearint);

if(weekofYear1 > 51 && month == 1){

if(weekofYear1 > 51){

weekofYear1 = 1;

}

}

//当前周数 * 7 是否小于 当日处于一年中的第几天

if(weekofYear1 * 7 < c.get(Calendar.DAY_OF_YEAR)){

weekofYear1++;

}

System.out.println(weekofYear1);

System.out.println("一年中第多少天"+c.get(Calendar.DAY_OF_YEAR));

}

}