SimpleDateFormat matter1=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");//格式化时间格式
               Date nowTime=new Date();//获取当前时间
                String   tmf= matter1.format(nowTime);


                             Date now=matter1.parse(tmf);
                                Date end=matter1.parse(atime);//atime是数据库中事前存的时间
                               long cha=(now.getTime()-end.getTime())/ (1000 * 60 * 60 * 24);//计算时间差
                            
                             System.out.println("一号时间差事："+cha);

------解决方案--------------------
可以将时间存的时候存成long型，算时间差就简单多了，这是存放时间值的方法
public static long getLongTime()
   {
       try
       {
           long l = 0L;
           Calendar calendar = Calendar.getInstance();
           String s = String.valueOf(calendar.get(1));
           String s1 = String.valueOf(calendar.get(2) + 1);
           String s2 = String.valueOf(calendar.get(5));
           String s3 = String.valueOf(calendar.get(10));
           String s4 = String.valueOf(calendar.get(9));
           String s5 = String.valueOf(calendar.get(12));
           String s6 = String.valueOf(calendar.get(13));
           if(s4.equals("1"))
               s3 = String.valueOf(Long.parseLong(s3) + 12L);
           if(s1.length() < 2)
               s1 = "0" + s1;
           if(s2.length() < 2)
               s2 = "0" + s2;
           if(s3.length() < 2)
               s3 = "0" + s3;
           if(s5.length() < 2)
               s5 = "0" + s5;
           if(s6.length() < 2)
               s6 = "0" + s6;
           l = Long.parseLong(s + s1 + s2 + s3 + s5 + s6);
           return l;
       }
       catch(Exception exception)
       {
           return 0L;
       }
   }

------解决方案--------------------
SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
  java.util.Date now = df.parse("2008-03-26 13:31:40");
  java.util.Date date=df.parse("2008-01-02 11:30:24");
  long l=now.getTime()-date.getTime();
  long day=l/(24*60*60*1000);
  long hour=(l/(60*60*1000)-day*24);
  long min=((l/(60*1000))-day*24*60-hour*60);
  long s=(l/1000-day*24*60*60-hour*60*60-min*60);
  System.out.println(""+day+"天"+hour+"小时"+min+"分"+s+"秒");