xml 读写 demo

以下是一个简单的Java XML读写示例：

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;

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;

public class XmlDemo {
    
    public static void main(String[] args) {
        try {
            // 创建XML文档
            DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
            DocumentBuilder builder = factory.newDocumentBuilder();
            Document doc = builder.newDocument();
            
            // 创建根元素
            Element root = doc.createElement("books");
            doc.appendChild(root);
            
            // 创建子元素
            Element book1 = doc.createElement("book");
            book1.setAttribute("id", "1");
            Element name1 = doc.createElement("name");
            name1.setTextContent("Java编程思想");
            Element author1 = doc.createElement("author");
            author1.setTextContent("Bruce Eckel");
            book1.appendChild(name1);
            book1.appendChild(author1);
            
            Element book2 = doc.createElement("book");
            book2.setAttribute("id", "2");
            Element name2 = doc.createElement("name");
            name2.setTextContent("Java核心技术");
            Element author2 = doc.createElement("author");
            author2.setTextContent("Cay Horstmann");
            book2.appendChild(name2);
            book2.appendChild(author2);
            
            // 添加子元素到根元素
            root.appendChild(book1);
            root.appendChild(book2);
            
            // 将XML文档写入文件
            TransformerFactory transformerFactory = TransformerFactory.newInstance();
            Transformer transformer = transformerFactory.newTransformer();
            DOMSource source = new DOMSource(doc);
            StreamResult result = new StreamResult(new File("books.xml"));
            transformer.transform(source, result);
            
            // 读取XML文档
            File xmlFile = new File("books.xml");
            DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
            DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
            Document xml = dBuilder.parse(xmlFile);
            xml.getDocumentElement().normalize();
            
            // 获取所有book元素
            NodeList nList = xml.getElementsByTagName("book");
            List<Book> books = new ArrayList<>();
            for (int i = 0; i < nList.getLength(); i++) {
                Node nNode = nList.item(i);
                if (nNode.getNodeType() == Node.ELEMENT_NODE) {
                    Element eElement = (Element) nNode;
                    String id = eElement.getAttribute("id");
                    String name = eElement.getElementsByTagName("name").item(0).getTextContent();
                    String author = eElement.getElementsByTagName("author").item(0).getTextContent();
                    books.add(new Book(id, name, author));
                }
            }
            
            // 打印所有book元素
            for (Book book : books) {
                System.out.println(book);
            }
        } catch (ParserConfigurationException | SAXException | IOException | TransformerException e) {
            e.printStackTrace();
        }
    }
    
    static class Book {
        private String id;
        private String name;
        private String author;
        
        public Book(String id, String name, String author) {
            this.id = id;
            this.name = name;
            this.author = author;
        }
        
        public String getId() {
            return id;
        }
        
        public void setId(String id) {
            this.id = id;
        }
        
        public String getName() {
            return name;
        }
        
        public void setName(String name) {
            this.name = name;
        }
        
        public String getAuthor() {
            return author;
        }
        
        public void setAuthor(String author) {
            this.author = author;
        }
        
        @Override
        public String toString() {
            return "Book [id=" + id + ", name=" + name + ", author=" + author + "]";
        }
    }
}

该示例创建了一个XML文档，包含两本书的信息，并将文档写入文件。然后它从文件中读取XML文档，解析出所有的book元素，并将它们打印出来。在这个示例中，我们使用了Java自带的DOM API来读写XML文件，同时也使用了XPath来查找元素。