XPath 从父节点和子节点中选择属性值

Question

以下是我的 XML 文件：

<?xml version="1.0" encoding="UTF-8"?>
   <query xmlns:yahoo="http://www.yahooapis.com/v1/base.rng" yahoo:lang="en-GB">
      <results>

        <sector sectorid="1" sectorname="Basic Materials">
          <industry id="112" name="Agricultural Chemicals"/>
          <industry id="132" name="Aluminum"/>
          <industry id="110" name="Chemicals - Major Diversified"/>
          <industry id="131" name="Copper"/>
          <industry id="134" name="Gold"/>
          <industry id="121" name="Independent Oil and Gas"/>
          <industry id="120" name="Major Integrated Oil and Gas"/>
        </sector>

        <sector sectorid="2" sectorname="Conglomerates">
          <industry id="210" name="Conglomerates"/>
        </sector>

        <sector sectorid="7" sectorname="Services">
          <industry id="720" name="Advertising Agencies"/>
          <industry id="773" name="Air Delivery and Freight Services"/>
          <industry id="772" name="Air Services and Others"/>
          <industry id="730" name="Apparel Stores"/>
          <industry id="744" name="Auto Dealerships"/>
        </sector>

     </results>
   </query>

从上面的 XML 文件中，我希望将属性值：sectorid、id 和 name 存储在适当的变量中（我正在使用 Java）。我一直在查看不同的 XPath 表达式，并想出了以下代码，但是，在存储 id 属性的值时会引发 java.lang.NumberFormatException: For input string: "" 异常。这是我的代码：

public class XMLToDatabase {

    private static int __SectorID;
    private static int __IndustryID;
    private static String __IndustryName;

    public static void main(String[] args) throws SQLException, UnsupportedEncodingException, ParserConfigurationException, SAXException, IOException, XPathExpressionException {

        try {               
            File _XMLFile = new File("SectorsAndIndustries.xml");

            DocumentBuilderFactory _DocumentBuilderFactory = DocumentBuilderFactory.newInstance();
            _DocumentBuilderFactory.setNamespaceAware(true);

            DocumentBuilder _DocumentBuilder = _DocumentBuilderFactory.newDocumentBuilder();
            Document _Document = _DocumentBuilder.parse(_XMLFile);  

            _Document.getDocumentElement().normalize();

            XPath _XPath = XPathFactory.newInstance().newXPath();

            XPathExpression _XPathExpression = _XPath.compile("//sector | //industry");

            NodeList _NodeList = (NodeList) _XPathExpression.evaluate(_Document, XPathConstants.NODESET);


            for (int i = 0; i < _NodeList.getLength(); i++) {
                Node _Node = _NodeList.item(i);

                if(_Node.getNodeType() == Node.ELEMENT_NODE) {
                    Element _Element = (Element) _Node;

                    __SectorID = Integer.parseInt(_Element.getAttribute("sectorid"));
                    __IndustryID = Integer.parseInt(_Element.getAttribute("id"));
                    __IndustryName = _Element.getAttribute("name");
                }

            System.out.println(__SectorID + ", " + __IndustryID + ", " + __IndustryName);
            }
        } catch (Exception e) {
             e.printStackTrace();
        }

    }

}

有人可以帮我确定是XPath Expression 我犯了错误，还是我存储第二个变量__IndustryID 的方式？因为第一个变量__SectorID 正确存储了值1，但是对于__IndustryID 抛出了上面提到的异常。理想情况下，我希望在每次执行 for 循环时存储所有 3 个属性的值，以将它们保存到数据库表中。如果需要更多信息，请告诉我。

Answer 1

据我所知，您正在编译一个节点列表，其中包含sector 或industry 元素的节点。对于其中的每一个，您都希望检索 sectorid 和 id 属性 - 但显然，没有任何元素同时具有这两个属性。

更好的方法是

• 找到所有 sector 元素并为每个元素打印出扇区 ID
• 对于每个 sector 元素，遍历其所有称为 industry 的子元素（这需要对每个 sector 元素应用第二个 XPath 表达式，但这是一个微不足道的表达式："industry"）
• 并输出每个industry的ID属性

Answer 2

Mathias 提出了正确的方法，我提出了一个稍作修改的解决方案：

public class XMLToDatabase {

    private static int __SectorID;
    private static int __IndustryID;
    private static String __IndustryName;

    public static void main(String[] args) throws SQLException,
            UnsupportedEncodingException, ParserConfigurationException,
            SAXException, IOException, XPathExpressionException {

        try {
            File _XMLFile = new File("C:/Users/Sachin/Desktop/SectorsAndIndustries.xml");
            DocumentBuilderFactory _DocumentBuilderFactory = DocumentBuilderFactory.newInstance();
            DocumentBuilder _DocumentBuilder = _DocumentBuilderFactory.newDocumentBuilder();
            Document _Document = _DocumentBuilder.parse(_XMLFile);
            _Document.getDocumentElement().normalize();

            XPath _XPath = XPathFactory.newInstance().newXPath();

            NodeList _NodeList1 = (NodeList) _XPath.evaluate("/results/sector", _Document, XPathConstants.NODESET);

            for (int i = 0; i < _NodeList1.getLength(); i++) {
                Element _Element1 = (Element) _NodeList1.item(i);

                __SectorID = Integer.parseInt(_Element1.getAttribute("sectorid"));

                NodeList _NodeList2 = (NodeList) _XPath.evaluate("industry", _Element1, XPathConstants.NODESET);

                for (int k=0; k < _NodeList2.getLength(); k++) {
                    __IndustryID = Integer.parseInt(_XPath.evaluate("industry[position()=" + (k + 1) + "]/@id", _Element1));
                    __IndustryName = _XPath.evaluate("industry[position()=" + (k + 1) + "]/@name", _Element1);

                    System.out.println(__SectorID + ", " + __IndustryID + ", " + __IndustryName);
                }
                System.out.println("\n-----------\n");
            }

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}