import java.text.SimpleDateFormat;
import java.util.Calendar;

public class DateHelper {
    /**
     * 當前月第一天
     * @return
     */
    public static String getFirstDayOfMonth(){
        SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd 00:00:00");
        Calendar lastDate = Calendar.getInstance();
        lastDate.set(Calendar.DATE,1);//設為當前月的1 號
        lastDate.add(Calendar.MONTH,-1);//加一個月，變為下月的1 號
        return sdf.format(lastDate.getTime());
    }

    /**
     * 計算當月最後一天
     * @return
     */
    public static String getLastDayOfMonth(){
        SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd 23:59:59");
        Calendar lastDate = Calendar.getInstance();
        lastDate.set(Calendar.DATE,1);//設為當前月的1 號
        lastDate.add(Calendar.DATE,-1);//減去一天，變為當月最後一天
        return sdf.format(lastDate.getTime());
    }

    /**
     * 獲取年月
     * @return
     */
    public static String getThisYearAndMonth(){
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM");
        return sdf.format(getFirstDayOfMonth());
    }

}