Calendar 獲取本週週一、週五時間，以及獲取當月第一天

package common.util;


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


public class WorkDay {
/**
* 得到本週週一日期
* @return
*/
public static String getWeekMonday(){
SimpleDateFormat formater=new SimpleDateFormat("MM/dd/yyyy");
Calendar cal=new GregorianCalendar();
cal.setFirstDayOfWeek(Calendar.MONDAY);
cal.setTime(new Date());
cal.set(Calendar.DAY_OF_WEEK, cal.getFirstDayOfWeek());
Date first=cal.getTime();
return formater.format(first);
}
/**
* 得到本週週五日期
* @return
*/
public static String getWeekFriday(){
SimpleDateFormat formater=new SimpleDateFormat("MM/dd/yyyy");
Calendar cal=new GregorianCalendar();
        cal.setFirstDayOfWeek(Calendar.MONDAY);
        cal.set(Calendar.DAY_OF_WEEK, cal.getFirstDayOfWeek() + 4);
        Date last=cal.getTime();
        return  formater.format(last);
}
/**
* 獲取當月第一天
* @return
*/
public static String getMonthFirstday(){
SimpleDateFormat formater=new SimpleDateFormat("MM/dd/yyyy");
Calendar c = Calendar.getInstance();    
         c.add(Calendar.MONTH, 0);
         c.set(Calendar.DAY_OF_MONTH,1);//設置爲1號,當前日期既爲本月第一天 
         String first = formater.format(c.getTime());
    return first;
}
}