xml结构如下：
<province>
<title>北京</title>
<item>
<city>东城</city>
<city>西城</city>
<city>崇文</city>
<city>宣武</city>
<city>朝阳</city>
<city>丰台</city>
<city>石景山</city>
<city>海淀</city>
<city>门头沟</city>
<city>房山</city>
<city>通州</city>
<city>顺义</city>
<city>昌平</city>
<city>大兴</city>
<city>平谷</city>
<city>怀柔</city>
<city>密云</city>
<city>延庆</city>
</item>
</province>
<province>
<title>上海</title>
<item>
<city>黄浦</city>
<city>卢湾</city>
<city>徐汇</city>
<city>长宁</city>
<city>静安</city>
<city>普陀</city>
<city>闸北</city>
<city>虹口</city>
<city>杨浦</city>
<city>闵行</city>
<city>宝山</city>
<city>嘉定</city>
<city>浦东</city>
<city>金山</city>
<city>松江</city>
<city>青浦</city>
<city>南汇</city>
<city>奉贤</city>
<city>崇明</city>
</item>
</province> <province>
<title>北京</title>
<item>
<city>东城</city>
<city>西城</city>
<city>崇文</city>
<city>宣武</city>
<city>朝阳</city>
<city>丰台</city>
<city>石景山</city>
<city>海淀</city>
<city>门头沟</city>
<city>房山</city>
<city>通州</city>
<city>顺义</city>
<city>昌平</city>
<city>大兴</city>
<city>平谷</city>
<city>怀柔</city>
<city>密云</city>
<city>延庆</city>
</item>
</province>
<province>
<title>上海</title>
<item>
<city>黄浦</city>
<city>卢湾</city>
<city>徐汇</city>
<city>长宁</city>
<city>静安</city>
<city>普陀</city>
<city>闸北</city>
<city>虹口</city>
<city>杨浦</city>
<city>闵行</city>
<city>宝山</city>
<city>嘉定</city>
<city>浦东</city>
<city>金山</city>
<city>松江</city>
<city>青浦</city>
<city>南汇</city>
<city>奉贤</city>
<city>崇明</city>
</item>
</province>