一个日期帮助类

package com.fh.util;

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

public class DateUtil {
   private final static SimpleDateFormat sdfYear = new SimpleDateFormat("yyyy");

   private final static SimpleDateFormat sdfDay = new SimpleDateFormat(
         "yyyy-MM-dd");
   
   private final static SimpleDateFormat sdfDays = new SimpleDateFormat(
   "yyyyMMdd");

   private final static SimpleDateFormat sdfTime = new SimpleDateFormat(
         "yyyy-MM-dd HH:mm:ss");

   /**
    * 获取YYYY格式
    * 
    * @return
    */
   public static String getYear() {
      return sdfYear.format(new Date());
   }

   /**
    * 获取YYYY-MM-DD格式
    * 
    * @return
    */
   public static String getDay() {
      return sdfDay.format(new Date());
   }
   
   /**
    * 获取YYYYMMDD格式
    * 
    * @return
    */
   public static String getDays(){
      return sdfDays.format(new Date());
   }

   /**
    * 获取YYYY-MM-DD HH:mm:ss格式
    * 
    * @return
    */
   public static String getTime() {
      return sdfTime.format(new Date());
   }

   /**
   * @Title: compareDate
   * @Description: TODO(日期比较，如果s>=e 返回true 否则返回false)
   * @param s
   * @param e
   * @return boolean  
   * @throws
   * @author luguosui
    */
   public static boolean compareDate(String s, String e) {
      if(fomatDate(s)==null||fomatDate(e)==null){
         return false;
      }
      return fomatDate(s).getTime() >=fomatDate(e).getTime();
   }

   /**
    * 格式化日期
    * 
    * @return
    */
   public static Date fomatDate(String date) {
      DateFormat fmt = new SimpleDateFormat("yyyy-MM-dd");
      try {
         return fmt.parse(date);
      } catch (ParseException e) {
         e.printStackTrace();
         return null;
      }
   }

   /**
    * 校验日期是否合法
    * 
    * @return
    */
   public static boolean isValidDate(String s) {
      DateFormat fmt = new SimpleDateFormat("yyyy-MM-dd");
      try {
         fmt.parse(s);
         return true;
      } catch (Exception e) {
         // 如果throw java.text.ParseException或者NullPointerException，就说明格式不对
         return false;
      }
   }
   public static int getDiffYear(String startTime,String endTime) {
      DateFormat fmt = new SimpleDateFormat("yyyy-MM-dd");
      try {
         long aa=0;
         int years=(int) (((fmt.parse(endTime).getTime()-fmt.parse(startTime).getTime())/ (1000 * 60 * 60 * 24))/365);
         return years;
      } catch (Exception e) {
         // 如果throw java.text.ParseException或者NullPointerException，就说明格式不对
         return 0;
      }
   }
     /**
     * <li>功能描述：时间相减得到天数
     * @param beginDateStr
     * @param endDateStr
     * @return
     * long 
     * @author Administrator
     */
    public static long getDaySub(String beginDateStr,String endDateStr){
        long day=0;
        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
        Date beginDate = null;
        Date endDate = null;
        
            try {
            beginDate = format.parse(beginDateStr);
            endDate= format.parse(endDateStr);
         } catch (ParseException e) {
            e.printStackTrace();
         }
            day=(endDate.getTime()-beginDate.getTime())/(24*60*60*1000);
            //System.out.println("相隔的天数="+day);
      
        return day;
    }
    
    /**
     * 得到n天之后的日期
     * @param days
     * @return
     */
    public static String getAfterDayDate(String days) {
       int daysInt = Integer.parseInt(days);
       
        Calendar canlendar = Calendar.getInstance(); // java.util包
        canlendar.add(Calendar.DATE, daysInt); // 日期减 如果不够减会将月变动
        Date date = canlendar.getTime();
        
//        SimpleDateFormat sdfd = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String dateStr = sdfDay.format(date);
        
        return dateStr;
    }
    
    /**
     * 得到n天之后是周几
     * @param days
     * @return
     */
    public static String getAfterDayWeek(String days) {
       int daysInt = Integer.parseInt(days);
       
        Calendar canlendar = Calendar.getInstance(); // java.util包
        canlendar.add(Calendar.DATE, daysInt); // 日期减 如果不够减会将月变动
        Date date = canlendar.getTime();
        
        SimpleDateFormat sdf = new SimpleDateFormat("E");
        String dateStr = sdf.format(date);
        
        return dateStr;
    }


    //获取上月前一天日期
    public static String getLastMonthDate(){
      Calendar c = Calendar.getInstance();
      c.add(Calendar.MONTH, -1);
      c.add(Calendar.DATE,+1);
      return  sdfDay.format(c.getTime());
   }

    public static void main(String[] args) {
       System.out.println(getLastMonthDate());
//     System.out.println(getAfterDayWeek("3"));
    }

}