按月寻找第一天与最后一天

protected String findTheFirstDayInMonth(String date){
    String yearAndMonth = date.substring(0,8);
    String day = "01";

    return yearAndMonth + day;
}

protected String findTheLastDayInLastMonth(String date){
    String year = date.substring(0,4);
    String month = date.substring(5,7);
    Integer y = Integer.valueOf(year);
    Integer m = Integer.valueOf(month);

    if(m == 01){
        y = y - 1;
        m = 12;
        month = "0"+m.toString();
        year = y.toString();
    }else {
        m = m -1;
        if(m<10){
            month = "0"+m.toString();
        }else {
            month = m.toString();
        }
    }

    switch (month){
        case "01" :
        case "03" :
        case "05" :
        case "07" :
        case "08" :
        case "10" :
        case "12" :
            return year+"-"+month+"-"+"31";
        case "02" :
            return y % 4 == 0 && y % 100 != 0 || y % 400 == 0 ? year+"-"+month+"-"+"29" : year+"-"+month+"-"+"28";

        case "04" :
        case "06" :
        case "09" :
        case "11" :
            return year+"-"+month+"-"+"30";
        default:
            return year+"-"+month+"-"+"30";
    }
}