java 实现获取当天，当周，当月，当季，当年的时间段

    由于项目需求，现在要做一个排行榜，需要按照时间（日，周，月，季，年）来从sql中查询数据。

 1、首先要做的就是怎样判断当前的时间段 

     查询资料知：

             项目中关于时间的使用：

1、获取时间  Date date=new Date(); date.getDate();    // System.currentTimeMills();  都是返回long型的数据，

2、以某种格式输出   

（1）SimpleDateFormat sdf=new SimpleDateFormat("yyyy--MM--dd HH:mm:ss " ); sdf.format(date)将date型转换成 String

（2）将String转换成Date型 ： sdf.parse(str); 将String类型解析成Date类型

3、对时间进行处理

Calendar 类 可以获取年月日

参看 http://www.apihome.cn/api/java/Calendar.html Calendar的使用文档

        /**
	 * 获取当前日期与周一相差的天数
	 * @return
	 */
	public static int getMondayPlus(){
		Calendar day=Calendar.getInstance();
		int dayOfWeek=day.get(Calendar.DAY_OF_WEEK);
		if(dayOfWeek==1){ //一周中第一天（周日）
			return -6;
		}else{
			return 2-dayOfWeek;
		}
	}
	/**
	 * 获得当天的起始时间
	 * @return
	 */
	public static Calendar getStartDate(Calendar today){
		today.set(Calendar.HOUR_OF_DAY,0);
		today.set(Calendar.MINUTE, 0);  
		today.set(Calendar.SECOND, 0);  
		today.set(Calendar.MILLISECOND, 0);  
		return today;
	}
	/**
	 * 获取当天截止时间
	 * @return
	 */
	public static Calendar getEndDate(Calendar endToday){
		endToday.set(Calendar.HOUR_OF_DAY, 23);  
		endToday.set(Calendar.MINUTE, 59);  
		endToday.set(Calendar.SECOND, 59);  
		endToday.set(Calendar.MILLISECOND, 59);  
		return endToday;
	}
	/**
	 * 获得当月起始时间
	 * @return
	 */
	public static Calendar getStartMounth(Calendar today){
		Calendar calendar = getStartDate(today);   
        calendar.set(Calendar.DAY_OF_MONTH, calendar.getActualMinimum(Calendar.DAY_OF_MONTH)); 
       	return calendar;
	}
	/**
	 * 获得当月结束时间
	 * @return
	 */
	public static Calendar getEndMounth(Calendar endToday){
		Calendar endMounth=getEndDate(endToday);
		endMounth.set(Calendar.DAY_OF_MONTH, endMounth.getActualMaximum(endMounth.DAY_OF_MONTH));
		return endMounth;
	}
	/**
	 * 获取当前季度 起始时间
	 * @return
	 */
	public static Calendar getStartQuarter(Calendar today){
         int currentMonth = today.get(Calendar.MONTH) + 1; 
		 try { 
	            if (currentMonth >= 1 && currentMonth <= 3) 
	            	today.set(Calendar.MONTH, 0); 
	            else if (currentMonth >= 4 && currentMonth <= 6) 
	            	today.set(Calendar.MONTH, 3); 
	            else if (currentMonth >= 7 && currentMonth <= 9) 
	            	today.set(Calendar.MONTH, 4); 
	            else if (currentMonth >= 10 && currentMonth <= 12) 
	            	today.set(Calendar.MONTH, 9); 
	        } catch (Exception e) { 
	            e.printStackTrace(); 
	        } 
		return today;
	}
	/**
	 * 获取当季的结束时间
	 */
	public static Calendar getEndQuarter(Calendar today){
	        int currentMonth = today.get(Calendar.MONTH) + 1; 
	        try { 
	            if (currentMonth >= 1 && currentMonth <= 3) { 
	            	today.set(Calendar.MONTH, 2); 
	            	today.set(Calendar.DATE, 31); 
	            } else if (currentMonth >= 4 && currentMonth <= 6) { 
	            	today.set(Calendar.MONTH, 5); 
	            	today.set(Calendar.DATE, 30); 
	            } else if (currentMonth >= 7 && currentMonth <= 9) { 
	            	today.set(Calendar.MONTH,8); 
	            	today.set(Calendar.DATE, 30); 
	            } else if (currentMonth >= 10 && currentMonth <= 12) { 
	            	today.set(Calendar.MONTH, 11); 
	            	today.set(Calendar.DATE, 31); 
	            } 
	        } catch (Exception e) { 
	            e.printStackTrace(); 
	        } 
	        return today; 
	}
	/**
	 * 获取当年起始时间
	 */
	public static Calendar getStartYear(Calendar today){
        try { 
        	today.set(Calendar.MONTH, 0); 
        	today.set(Calendar.DAY_OF_MONTH, today.getActualMinimum(Calendar.DAY_OF_MONTH)); 
        } catch (Exception e) { 
            e.printStackTrace(); 
        } 
        return today; 
	}
	/**
	 * 获取当年结束时间
	 */
	public static Calendar getEndYear(Calendar today){
		 try { 
	        	today.set(Calendar.MONTH, 11); 
	            today.set(Calendar.DAY_OF_MONTH, today.getMaximum(Calendar.DAY_OF_MONTH)); 
	      } catch (Exception e) { 
	            e.printStackTrace(); 
	      } 
	      return today; 
	}