用Java读取XML文件

Question

我正在从XML文件读取特定信息。我在尝试读取某些元素（例如DataDate）时遇到问题。我收到了NullPointerException。我认为这是因为在XML文件中有两个带有单词“ Project”的节点，而第一个没有DataDate。

我不知道如何解决此错误。

这是我正在阅读的XML文件的一部分：

package testReadXML;

import java.io.File;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.DocumentBuilder;
import org.w3c.dom.Document;
import org.w3c.dom.NodeList;
import org.w3c.dom.Node;
import org.w3c.dom.Element;

public class TestReadXML {

    public static void main(String[] args) {

        try {   

            File xmlFile = new File("C:/Users/diani/Downloads/XML Files/CS01.xml");

            DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
            DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
            Document doc = dBuilder.parse(xmlFile);

            doc.getDocumentElement().normalize();
            System.out.println("Root element:" + doc.getDocumentElement().getNodeName());

                NodeList nList = doc.getElementsByTagName("Project");

                for (int i = 0; i < nList.getLength(); i ++) {

                    Node nNode = nList.item(i);
                    System.out.println("\n" + nNode.getNodeName());

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

                            Element eElement = (Element) nNode;

                            System.out.println("Object Id : " + eElement.getAttribute("ObjectId"));
                            System.out.println("Id : " + eElement.getElementsByTagName("Id").item(0).getTextContent());
                            System.out.println("Name : " + eElement.getElementsByTagName("Name").item(0).getTextContent());         
                            System.out.println("Data Date : " + eElement.getElementsByTagName("DataDate").item(0).getTextContent());  
                        }
                }

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

Answer 1

在获取元素时只需添加此If条件

 if(eElement.getElementsByTagName("DataDate").getLength() > 0) {

                        System.out.println("Object Id : " + eElement.getAttribute("ObjectId"));
                        System.out.println("Id : " + eElement.getElementsByTagName("Id").item(0).getTextContent());
                        System.out.println("Name : " + eElement.getElementsByTagName("Name").item(0).getTextContent());
                        System.out.println("Data Date : " + eElement.getElementsByTagName("DataDate").item(0).getTextContent());
                    }