从 XML 文件获取数据时出现问题

问：

我尝试过使用 DOM、Xpath，目前我只成功地使用流来遍历每一行并以这种方式获取数据。显然，我的 shelfNodeLists.getAttributes.getNamedItem 会产生它，我不明白它为什么要这样做。在任何当前论坛上都找不到任何相关信息。

我真的在努力让 DOM 工作，因为我有大量的 XML 文件要迭代，而且我听说它对大量数据很有效。

这是我得到的 NPE。

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "org.w3c.dom.Node.getTextContent()" because the return value of "org.w3c.dom.NamedNodeMap.getNamedItem(String)" is null
    at ReadXmlDomParser.main(ReadXmlDomParser.java:75)

下面是产生异常的代码：

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

import org.xml.sax.SAXException;

import javax.xml.XMLConstants;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;

import java.io.File;
import java.io.IOException;


public class ReadXmlDomParser {

    private static final String FILENAME = "src/main/resources/TestXML.xml";

    public static void main(String[] args) {
        // Instantiate the Factory
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        try {

            // process XML
            dbf.setFeature(XMLConstants.FEATURE_SECURE_PROCESSING, true);

            // parse XML file
            DocumentBuilder db = dbf.newDocumentBuilder();
            Document doc = db.parse(new File(FILENAME));
            doc.getDocumentElement().normalize();

            System.out.println("Root Element :" + doc.getDocumentElement().getNodeName());
            System.out.println("------");

            // get <Shelf>
            NodeList list = doc.getElementsByTagName("Shelf");

            for (int temp = 0; temp < list.getLength(); temp++) {

                Node node = list.item(temp);

                if (node.getNodeType() == Node.ELEMENT_NODE) {

                    Element element = (Element) node;

                    // get shelf's attribute
                    String id = element.getAttribute("ShelfID");

                    // get text
                    String positionText = element.getElementsByTagName("Position").item(0).getTextContent();
                    String dangerLevelText = element.getElementsByTagName("DangerLevel").item(0).getTextContent();
                    String coffeeText = element.getElementsByTagName("Coffee").item(0).getTextContent();

                    NodeList shelfNodeList = element.getElementsByTagName("Position");
                    NodeList shelfNodeList1 = element.getElementsByTagName("DangerLevel");
                    NodeList shelfNodeList2 = element.getElementsByTagName("Coffee");

                    //get attributes
                    String position = shelfNodeList.item(0).getAttributes().getNamedItem("Position").getTextContent();
                    String dangerLevel = shelfNodeList1.item(0).getAttributes().getNamedItem("DangerLevel").getTextContent();
                    String coffee = shelfNodeList2.item(0).getAttributes().getNamedItem("Coffee").getTextContent();


                    System.out.println("Current Element :" + node.getNodeName());
                    System.out.println("Player Id : " + id);
                    System.out.printf("Position : %,.2f [%s]%n%n", Float.parseFloat(positionText), position);
                    System.out.printf("DangerLevel [Stat] : %,.2f [%s]%n%n", Float.parseFloat(dangerLevelText), dangerLevel);
                    System.out.printf("Coffee [Stat] : %,.2f [%s]%n%n", Float.parseFloat(coffeeText), coffee);
                }
            }
        } catch (ParserConfigurationException | SAXException | IOException e) {
            e.printStackTrace();
        }

    }

}

这是我尝试从中提取数据的XML文件：

<Section>
    <Shelf ShelfID="p60772">
        <Position BioChemicalID="Bio1523">1</Position>
        <Position BioChemicalID="Bio9612">4</Position>
        <DangerLevel scale="1-10"> 6</DangerLevel>
        <DangerLevel scale="1-10"> 2</DangerLevel>
        <Coffee java="Yes"> 100%</Coffee>
    </Shelf>
</Section>