CalendarHelper日期计算工具，各种日期的获取和计算

package com.ran.interview;

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.Locale;

/**
 * @author BMR
 * @ClassName: CalendarHelper
 * @Description: 日期计算工具，标准格式yyyy-MM-dd下各种日期的获取和计算
 * @date 2016/2/26 16:08
 */
public class CalendarHelper {

    private static SimpleDateFormat yyyyMMddFormat;
    public final static String[] mMonthCN = new String[]{"一月", "二月", "三月", "四月", "五月", "六月", "七月", "八月",
            "九月", "十月", "十一月", "十二月"};


    public static void setup() {
        yyyyMMddFormat = new SimpleDateFormat("yyyy-MM-dd", Locale.ENGLISH);
    }


    /**
     * 显示格式化的月日：eg,2013-03-27，convert to 03月27日
     *
     * @param dateStr eg,2013-03-27
     * @return 03月27日
     */
    public static String formatToDay(String dateStr) {
        if (CalendarHelper.isStrEmpty(dateStr)) {
            return "";
        }
        //DateFormat localFormat = DateFormat.getDateInstance(DateFormat.MEDIUM, Locale.CHINA);
        DateFormat localFormat = DateFormat.getDateInstance(DateFormat.LONG, Locale.CHINESE);
        Date date;
        String formatDate = null;
        try {
            date = getDateFromString(dateStr, null);
            formatDate = localFormat.format(date);
            formatDate = formatDate.substring(5);
        } catch (ParseException e) {
            e.printStackTrace();
        }
        return formatDate;
    }

    /**
     * 显示格式化的月，中文的月份
     *
     * @param dateStr eg,2013-03-27
     * @return 三月
     */
    public static String formatToMonth(String dateStr) {
        if (CalendarHelper.isStrEmpty(dateStr)) {
            return "";
        }
        if(dateStr.length() < 7){
            return "";
        }
        String month = dateStr.substring(5, 7);
        int index = Integer.parseInt(month);
        String formatDate = "";
        if (index > 0 && index < 13) {
            formatDate = mMonthCN[index - 1];
        }
        return formatDate;
    }

    /**
     * 检查字符串是否是今天
     *
     * @param dateStr
     */
    public static boolean checkIsToday(String dateStr) {
        Calendar calendar = Calendar.getInstance();
        Date currentDate = calendar.getTime();
        return getStringFromDate(currentDate, null).equals(dateStr);

    }

    /**
     * Get the Date from String with custom format. Default format is yyyy-MM-dd
     *
     * @param dateString
     * @param dateFormat
     * @return
     * @throws ParseException
     */
    public static Date getDateFromString(String dateString, String dateFormat) throws ParseException {
        SimpleDateFormat formatter;
        if (dateFormat == null) {
            if (yyyyMMddFormat == null) {
                setup();
            }
            formatter = yyyyMMddFormat;
        } else {
            formatter = new SimpleDateFormat(dateFormat, Locale.ENGLISH);
        }

        return formatter.parse(dateString);
    }

    /**
     * Convert the Date to String with custom format. Default format is yyyy-MM-dd
     *
     * @param date
     * @param dateFormat
     * @return
     */
    public static String getStringFromDate(Date date, String dateFormat) {
        String dateString = null;
        SimpleDateFormat formatter;
        if (date == null) {
            return null;
        }
        if (dateFormat == null) {
            if (yyyyMMddFormat == null) {
                setup();
            }
            formatter = yyyyMMddFormat;
        } else {
            formatter = new SimpleDateFormat(dateFormat, Locale.ENGLISH);
        }
        dateString = formatter.format(date);
        return dateString;
    }


    /**
     * 获取当天的日期
     *
     * @return
     */
    public static String getTodayDateString() {
        SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd", Locale.ENGLISH);
        return dateFormat.format(new Date());
    }

    /**
     * 获取指定日期的偏移后的日期字符串，offset>0日期向后，<0向前
     *
     * @param dateStr
     * @param offset
     * @return
     */
    public static String getDateStringByOffset(String dateStr, int offset) {
        if (offset == 0) {
            return dateStr;
        }
        Date date;
        String newDateStr = null;
        try {
            date = getDateFromString(dateStr, null);
            Calendar cal = Calendar.getInstance();
            cal.setTime(date);
            cal.add(Calendar.DATE, offset);
            newDateStr = getStringFromDate(cal.getTime(), null);
        } catch (ParseException e) {
            e.printStackTrace();
        }
        return newDateStr;
    }

    /**
     * 获取输入日期所在周的开始日期 （周一），默认格式 yyyy-MM-dd
     *
     * @param date
     * @return String
     */
    public static String getFirstDayOfWeek(Date date, String dateFormat) {
        String firstDay;
        if (date == null) {
            return null;
        }
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(date);
        if (calendar.get(Calendar.DAY_OF_WEEK) == 1) {
            calendar.add(Calendar.DATE, -7);
        }
        calendar.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
        Date newDate = calendar.getTime();
        firstDay = getStringFromDate(newDate, dateFormat);
        return firstDay;
    }

    /**
     * 获取输入日期所在周的结束日期 （周日），默认格式 yyyy-MM-dd
     *
     * @param date
     * @return String
     */
    public static String getLastDayOfWeek(Date date, String dateFormat) {
        String lastDay;
        if (date == null) {
            return null;
        }
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(date);
        //  默认周日是本周的开始，
        if (calendar.get(Calendar.DAY_OF_WEEK) != 1) {
            // 非周末的情况要先加一周才能获得本周的周末
            calendar.add(Calendar.DATE, 7);
        }
        calendar.set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY);
        Date newDate = calendar.getTime();
        lastDay = getStringFromDate(newDate, dateFormat);
        return lastDay;
    }


    /**
     * 获得指定日期与指定周数间隔的那周周一的日期
     *
     * @param date       正数是count周数之后，负数时count周数之前，0 返回本周周一日期
     * @param dateFormat
     * @return
     */
    public static String getFirstDayOfPreviousWeek(Date date, int count, String dateFormat) {
        String firstDay;
        if (date == null) {
            return null;
        }
        if (count == 0) {
            return getFirstDayOfWeek(date, dateFormat);
        }

        Calendar calendar = Calendar.getInstance();
        calendar.setTime(date);
        // 默认周日是本周的开始，如果是周末,不加
        if (calendar.get(Calendar.DAY_OF_WEEK) == 1) {
            calendar.add(Calendar.DATE, (count - 1) * 7);
        } else {
            calendar.add(Calendar.DATE, count * 7);
        }

        calendar.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
        Date newDate = calendar.getTime();
        firstDay = getStringFromDate(newDate, dateFormat);
        return firstDay;
    }

    /**
     * 获得指定日期与指定周数间隔的那周周日的日期
     *
     * @param date       正数是count周数之后，负数时count周数之前，0 返回本周周日日期
     * @param dateFormat
     * @return
     */
    public static String getLastDayOfPreviousWeek(Date date, int count, String dateFormat) {
        String lastDay;
        if (date == null) {
            return null;
        }
        if (count == 0) {
            return getLastDayOfWeek(date, dateFormat);
        }

        Calendar calendar = Calendar.getInstance();
        calendar.setTime(date);
        // 默认周日是本周的开始，要先加一周才能获得本周的周末。如果是周末,不加
        if (calendar.get(Calendar.DAY_OF_WEEK) == 1) {
            calendar.add(Calendar.DATE, (count) * 7);
        } else {
            // 非周末的情况要先加一周才能获得本周的周末
            calendar.add(Calendar.DATE, (count + 1) * 7);
        }
        calendar.set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY);
        Date newDate = calendar.getTime();
        lastDay = getStringFromDate(newDate, dateFormat);
        return lastDay;
    }


    /**
     * 获取输入日期所在月的开始日期，默认格式 yyyy-MM-dd
     *
     * @param date
     * @return
     */
    public static String getFirstDayOfMonth(Date date, String dateFormat) {
        String firstDay;
        if (date == null) {
            return null;
        }
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(date);
        calendar.set(Calendar.DATE, 1);
        Date newDate = calendar.getTime();
        firstDay = getStringFromDate(newDate, dateFormat);
        return firstDay;
    }

    /**
     * 获取输入日期所在月的结束日期，默认格式 yyyy-MM-dd
     *
     * @param date
     * @return String
     */
    public static String getLastDayOfMonth(Date date, String dateFormat) {
        String lastDay;
        if (date == null) {
            return null;
        }
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(date);
        calendar.set(Calendar.DAY_OF_MONTH, calendar.getActualMaximum(Calendar.DAY_OF_MONTH));
        Date newDate = calendar.getTime();
        lastDay = getStringFromDate(newDate, dateFormat);
        return lastDay;
    }


    /**
     * 获取输入日期和间隔月份所在月的开始日期，默认格式 yyyy-MM-dd
     *
     * @param date
     * @param count
     * @return
     */
    public static String getFirstDayOfPreviousMonth(Date date, int count, String dateFormat) {
        String firstDay;
        if (date == null) {
            return null;
        }
        if (count == 0) {
            return getFirstDayOfMonth(date, dateFormat);
        }
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(date);
        calendar.add(Calendar.MONTH, count);
        calendar.set(Calendar.DATE, 1);
        Date newDate = calendar.getTime();
        firstDay = getStringFromDate(newDate, dateFormat);
        return firstDay;
    }


    /**
     * 获取输入日期和间隔月份所在月的最后日期，默认格式 yyyy-MM-dd
     *
     * @param date
     * @param count
     * @return
     */
    public static String getLastDayOfPreviousMonth(Date date, int count, String dateFormat) {
        String firstDay;
        if (date == null) {
            return null;
        }
        if (count == 0) {
            return getLastDayOfMonth(date, dateFormat);
        }
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(date);
        calendar.add(Calendar.MONTH, count);
        calendar.set(Calendar.DATE, calendar.getActualMaximum(Calendar.DAY_OF_MONTH));
        Date newDate = calendar.getTime();
        firstDay = getStringFromDate(newDate, dateFormat);
        return firstDay;
    }

    /**
     * 计算两个日期字符串之间的天数，格式2011-12-26
     *
     * @param dateStart 起始日期
     * @param dateEnd   结束日期
     * @return
     */
    public static int getIntervalDay(String dateStart, String dateEnd) {
        Date dateFrom;
        Date dateTo;
        long gap = 0;
        try {
            dateFrom = getDateFromString(dateStart, null);
            dateTo = getDateFromString(dateEnd, null);
            Calendar  cal = Calendar.getInstance();
            cal.setTime(dateFrom);
            long timeFrom = cal.getTimeInMillis();
            cal.setTime(dateTo);
            long timeTo = cal.getTimeInMillis();
            gap = (timeTo - timeFrom) / (1000 * 3600 * 24);
            gap = gap + 1;
            //从间隔毫秒变成间隔天数</strong>
        } catch (ParseException e) {
            e.printStackTrace();
        }
        return (int)gap;
    }
    
    /**
     * 判断字符串是否为空
     * 
     * @param str
     * @return
     */
    public static boolean isStrEmpty(String str) {
        if (null == str || "".equals(str.trim()) || "null".equals(str)) {
            return true;
        }
        return false;
    }
}

package com.ran.interview;

import java.util.Date;

/** 
* @ClassName: CalendarHelperTest 
* @Description: TODO
* @author BMR
* @date 2016年3月15日 上午11:00:49 
*/
public class CalendarHelperTest {
    
    public static void main(String[] args){
        String todayStr = CalendarHelper.getTodayDateString();
        
        System.out.println("today is： "+ todayStr);
        System.out.println("check is today： "+ CalendarHelper.checkIsToday(todayStr));
        System.out.println("today is (Chinese format)： "+ CalendarHelper.formatToDay(todayStr));
        System.out.println("今天所在周的周一： "+ CalendarHelper.getFirstDayOfWeek(new Date(), null));
        System.out.println("今天所在周的周末： "+ CalendarHelper.getLastDayOfWeek(new Date(), null));
        System.out.println("指定日期的格式化的月，中文的月份： "+ CalendarHelper.formatToMonth(todayStr));
        System.out.println("获取输入日期所在月的开始日期： "+ CalendarHelper.getFirstDayOfMonth(new Date(), null));
        System.out.println("获取输入日期所在月的结束日期： "+ CalendarHelper.getLastDayOfMonth(new Date(), null));
        System.out.println("获得指定日期与指定周数间隔的那周周一的日期： "+ CalendarHelper.getFirstDayOfPreviousWeek(new Date(), 2, null));
        System.out.println("获得指定日期与指定周数间隔的那周周末的日期： "+ CalendarHelper.getLastDayOfPreviousWeek(new Date(), -2, null));
        System.out.println("获取输入日期和间隔月份所在月的开始日期： "+ CalendarHelper.getFirstDayOfPreviousMonth(new Date(), 2, null));
        System.out.println("获取输入日期和间隔月份所在月的最后日期： "+ CalendarHelper.getLastDayOfPreviousMonth(new Date(), -2, null));
        System.out.println("计算两个日期字符串之间的天数： "+ CalendarHelper.getIntervalDay("2016-03-01", todayStr));
    
    }
}

today is： 2016-03-15
check is today： true
today is (Chinese format)： 3月15日
今天所在周的周一： 2016-03-14
今天所在周的周末： 2016-03-20
指定日期的格式化的月，中文的月份： 三月
获取输入日期所在月的开始日期： 2016-03-01
获取输入日期所在月的结束日期： 2016-03-31
获得指定日期与指定周数间隔的那周周一的日期： 2016-03-28
获得指定日期与指定周数间隔的那周周末的日期： 2016-03-06
获取输入日期和间隔月份所在月的开始日期： 2016-05-01
获取输入日期和间隔月份所在月的最后日期： 2016-01-31
计算两个日期字符串之间的天数： 15