获取某月的第一天、最后一天

 /**
     * 根据提供的年月日获取该月份的第一天
     */
    public String getSupportBeginDayofMonth(Date date) {
        date.getTime();
        Calendar startDate = Calendar.getInstance();
        startDate.setTime(date);
        startDate.set(Calendar.DAY_OF_MONTH, 1);
        startDate.set(Calendar.HOUR_OF_DAY, 0);
        startDate.set(Calendar.MINUTE, 0);
        startDate.set(Calendar.SECOND, 0);
        startDate.set(Calendar.MILLISECOND, 0);
        Date firstDate = startDate.getTime();
        //  SimpleDateFormat myFmt7=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        SimpleDateFormat myFmt7 = new SimpleDateFormat("yyyy-MM-dd");
        return myFmt7.format(firstDate);
    }

    /**
     * 根据提供的年月获取该月份的最后一天
     */
    public String getSupportEndDayofMonth(Date date) {
        Calendar startDate = Calendar.getInstance();
        startDate.setTime(date);
        startDate.set(Calendar.DAY_OF_MONTH, startDate.getActualMaximum(Calendar.DAY_OF_MONTH));
        startDate.set(Calendar.HOUR_OF_DAY, 23);
        startDate.set(Calendar.MINUTE, 59);
        startDate.set(Calendar.SECOND, 59);
        startDate.set(Calendar.MILLISECOND, 999);
        Date firstDate = startDate.getTime();
//   SimpleDateFormat myFmt7=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        SimpleDateFormat myFmt7 = new SimpleDateFormat("yyyy-MM-dd");
        return myFmt7.format(firstDate);
    }

/******************************************************************************/

String[] tradeDateRange = tradeDate.split(",");
String tradeDateBegin = tradeDateRange[0];
String tradeDateEnd = tradeDateRange[1];
if ((tradeDateRange[0].split("-")).length == 2) {
    Date begin = null;
    Date end = null;
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
    try {
        begin = sdf.parse(tradeDateBegin + "-01");//tradeDateBegin为“2018-05”，需要拼接日期
        end = sdf.parse(tradeDateEnd + "-01");
    } catch (ParseException e) {
        e.printStackTrace();
    }
    tradeDateBegin = getSupportBeginDayofMonth(begin);
    tradeDateEnd = getSupportEndDayofMonth(end);
}