java获取本月第一天，最后一天

获取本月第一天：

public static Date getMonthFirstDay(){
    Calendar calendar = Calendar.getInstance();
    calendar.setTime(new Date());
    calendar.set(Calendar.DAY_OF_MONTH,1);
    calendar.add(Calendar.MONTH,0);
    return calendar.getTime();
}

获取本月最后一天：

public static Date getMonthLastDay(){
    Calendar calendar = Calendar.getInstance();
    calendar.setTime(new Date());
    calendar.set(Calendar.DAY_OF_MONTH,0);
    calendar.add(Calendar.MONTH,1);
    return calendar.getTime();
}

获取下个月第一天：

public static Date getNextMonthFirstDay(){
    Calendar calendar = Calendar.getInstance();
    calendar.setTime(new Date());
    calendar.set(Calendar.DAY_OF_MONTH,1);
    calendar.add(Calendar.MONTH,1);
    return calendar.getTime();
}