根据指定日期获取周，月，年的开始和结束时间

/**
* 获取本周的第一天日期和最后一天日期（按中国周）
* @param todayTime :"2017-03-15"
* @return arr[0] 第一天日期 ；arr[1]最后一天日期
* @throws ParseException
*/
public static String[] getWeekStartandEndDate(String todayTime) throws ParseException{
String[] arr = new String[2];
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
Calendar cal = Calendar.getInstance();
cal.setTime(sdf.parse(todayTime));
int d = 0;
if(cal.get(Calendar.DAY_OF_WEEK)==1){
d = -6;
}else{
d = 2-cal.get(Calendar.DAY_OF_WEEK);
}
cal.add(Calendar.DAY_OF_WEEK, d);
//所在周开始日期
arr[0]=sdf.format(cal.getTime());
cal.add(Calendar.DAY_OF_WEEK, 6);
//所在周结束日期
arr[1]=sdf.format(cal.getTime());
       return arr;   
}
/**
* 获取指定月的第一天日期和最后一天日期
* @param todayTime:"2017-03-15"
* @return arr[0] 第一天日期 ；arr[1]最后一天日期
* @throws ParseException
*/
public static String[] getMonthStartAndEndDate(String todayTime) throws ParseException{
String[] arr = new String[2];
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
Calendar c = Calendar.getInstance();
c.setTime(sdf.parse(todayTime));
        c.set(Calendar.DAY_OF_MONTH, 1);
        arr[0] =sdf.format(c.getTime());
        c.set(Calendar.DAY_OF_MONTH, c.getActualMaximum(Calendar.DAY_OF_MONTH));  
        arr[1]=sdf.format(c.getTime());
       return arr;   

}
/**
* 获取指定年的第一天日期和最后一天日期
* @param todayTime :"2017-03-15"
* @return arr[0] 第一天日期 ；arr[1]最后一天日期
* @throws ParseException
*/
public static String[] getYearStartAndEndDate(String todayTime) throws ParseException{
String[] arr = new String[2];
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
Calendar c = Calendar.getInstance();
c.setTime(sdf.parse(todayTime));
        c.set(Calendar.DAY_OF_YEAR, 1);
        arr[0] =sdf.format(c.getTime());
        c.set(Calendar.DAY_OF_YEAR, c.getActualMaximum(Calendar.DAY_OF_YEAR));  
        arr[1]=sdf.format(c.getTime());
       return arr;   

}

/**
* 根据指定周获取开始，结束日期
* @param week “2017-24”
* @return
*/
public static String [] getStartEndByWeek(String week){
String[] weekArr = new String[2];
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
String[] arr = week.split("-");
Calendar c = Calendar.getInstance();
c.set(Calendar.YEAR, Integer.parseInt(arr[0]));
c.set(Calendar.WEEK_OF_YEAR, Integer.parseInt(arr[1]));
int dayOfWeek = c.get(Calendar.DAY_OF_WEEK) - 2;
    c.add(Calendar.DATE, -dayOfWeek); // 得到本周的第一天
    weekArr[0]=sdf.format(c.getTime());
    c.add(Calendar.DATE, 6); // 得到本周的最后一天
    weekArr[1] = sdf.format(c.getTime());
    return weekArr;    

}

/**
* 两个日期相关天数
* 
* @param startDate
* @param endDate
* @return
*/
public static long getDateDiff(String startDate, String endDate) {
long diff = 0;
try {
Date date1 = new SimpleDateFormat("yyyy-MM-dd").parse(startDate);
Date date2 = new SimpleDateFormat("yyyy-MM-dd").parse(endDate);
diff = (date1.getTime() - date2.getTime()) / (24 * 60 * 60 * 1000) > 0 ? (date1.getTime() - date2.getTime())
/ (24 * 60 * 60 * 1000)
: (date2.getTime() - date1.getTime()) / (24 * 60 * 60 * 1000);
} catch (ParseException e) {
}
return diff;
}