怎么抓取alexaz的排名数据。

比如:DayRank,WeekRank等都不能通过网页源代码找到。
<tr>
<td class="rank_left"><span id="DayRank"><img src="/Images/Load.gif" border="0"></span></td>
<td class="rank"><img src="http://alexa.chinaz.com/Images/Up_arrow.gif" border="0"> <font color="#329A02">15593</font></td>
<td class="rank"><span id="WeekRank"><img src="/Images/Load.gif" border="0"></span></td>
<td class="rank"><img src="http://alexa.chinaz.com/Images/Up_arrow.gif" border="0"> <font color="#329A02">1898</font></td>
<td class="rank"><span id="MonthRank"><img src="/Images/Load.gif" border="0"></span></td>
<td class="rank"><img src="http://alexa.chinaz.com/Images/Down_arrow.gif" border="0">  <font color="#FF0000">54257</font></td>
<td class="rank"><span id="QuarterRank"><img src="/Images/Load.gif" border="0"></span></td>
<td class="rank"><img src="http://alexa.chinaz.com/Images/Down_arrow.gif" border="0">  <font color="#FF0000">15981</font></td>
</tr>

补充：Java ,  Web 开发