获得每月 第一天 最后一天 java

private String getBeginDate(){
        Calendar begin = Calendar.getInstance();
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

        begin.set(Calendar.DAY_OF_MONTH, begin.getActualMinimum(Calendar.DAY_OF_MONTH));
        begin.set(Calendar.SECOND, 0);
        begin.set(Calendar.HOUR_OF_DAY, 0);
        begin.set(Calendar.MINUTE, 0);

        return sdf.format(begin.getTime());
    }

    private String getEndDate(){
        Calendar end = Calendar.getInstance();
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

        end.set(Calendar.DAY_OF_MONTH, end.getActualMaximum(Calendar.DAY_OF_MONTH));
        end.set(Calendar.SECOND, 59);
        end.set(Calendar.HOUR_OF_DAY, 23);
        end.set(Calendar.MINUTE, 59);

        return sdf.format(end.getTime());
    }