使用dom4j的xpath读取XML文件

在java中，使用dom4j读一个XML文件，该文件的格式很简单，如下：
<?xml version="1.0" ?>
<CityDetails>
<CityDetail>
<CityCode>BJS</CityCode>
<City>1</City>
<CityName>北京</CityName>
<CityEName>Beijing</CityEName>
<Country>1</Country>
<Province>1</Province>
<Airport>NAY,PEK</Airport>
</CityDetail>
<CityDetail>
<CityCode>SHA</CityCode>
<City>2</City>
<CityName>上海</CityName>
<CityEName>Shanghai</CityEName>
<Country>1</Country>
<Province>2</Province>
<Airport>PVG,SHA</Airport>
</CityDetail>
<CityDetail>
<CityCode>TSN</CityCode>
<City>3</City>
<CityName>天津</CityName>
<CityEName>Tianjin</CityEName>
<Country>1</Country>
<Province>3</Province>
<Airport>TSN</Airport>
</CityDetail>
<CityDetails>

读这个文件方法如下：

public static void main(String args[]) throws Exception {

SAXReader reader = new SAXReader();

String filePath = "src/resources/国内城市.xml";

File file = new File(filePath);

ArrayList<String> cityList = new ArrayList<String>();

        if (file.exists()) {
            Document document = reader.read(file);// 读取XML文件
            Element root = document.getRootElement();// 得到根节点

            String xPathString = "//CityDetails/CityDetail";
            List list = root.selectNodes(xPathString);
            Element cityDetail, city, cityName, province, country;
            Node cityNode, cityNameNode;
            int i = 0;

for (Object obj : list) {

cityDetail = (Element) obj;

//方法一，使用 elementText可以显示出子元素的text。
System.out.println(cityDetail.elementText("City")+":"+cityDetail.elementText("CityName"));

                //方法二，继续使用xpath，则只能显示第一个节点的元素，循环下面的都没变化，还是第一个节点。
                xPathString = "//CityDetail/City";
                cityNode = cityDetail.selectSingleNode(xPathString);

                city = (Element) cityNode;
                System.out.println(city.asXML());
                // System.out.println(city.getText());

                xPathString = "//CityDetail/CityName";
                cityNameNode = cityDetail.selectSingleNode(xPathString);
                cityName = (Element) cityNameNode;
                System.out.println(cityName.asXML());
                // System.out.println(cityName.getText());

                i++;
                if (i > 2)
                    break;

}

} else {
System.out.println("file not exists");

}

    }

    显示的结果是这样：

1:北京
<City>1</City>
<CityName>北京</CityName>
2:上海
<City>1</City>
<CityName>北京</CityName>
3:天津
<City>1</City>
<CityName>北京</CityName>

问题在于，在xpath读取到一个节点后，继续使用xpath读取子节点时，出现问题。所有循环读取的结果都是第一个子节点的值。如本测试中的“<City>1</City><CityName>北京/CityName>”。

补充：软件开发 , Java ,