双机热备份的切换时间是怎么确定的?

JFreeChart实现热点功能后会在页面上产生map信息
<map id="map0" name="map0">
<area shape="poly" coords="552,21,551,23,549,24,547,23,546,21,547,19,549,18,551,19,552,21,552,21" title="(上限, 12) = 200" alt="" href="displayPieAction.do?checkid=83&series=%C9%CF%CF%DE&section=12"/>
<area shape="poly" coords="546,322,552,322,552,328,546,328,546,322,546,322" title="(下限, 12) = 0" alt="" href="displayPieAction.do?checkid=83&series=%CF%C2%CF%DE&section=12"/>
<area shape="poly" coords="101,21,100,23,98,24,96,23,95,21,96,19,98,18,100,19,101,21,101,21" title="(上限, 1) = 200" alt="" href="displayPieAction.do?checkid=83&series=%C9%CF%CF%DE&section=1"/>
<area shape="poly" coords="95,322,101,322,101,328,95,328,95,322,95,322" title="(下限, 1) = 0" alt="" href="displayPieAction.do?checkid=83&series=%CF%C2%CF%DE&section=1"/>
</map>

但是我不知道是那个类可以给alt或target赋值，能在一个新的窗口中打开，怎样实现此功能