基于Java实现XML文件的解析与更新攻略

XML简介

Xml是一种用于存储和传输数据的标记语言。在Web应用程序中，Xml数据被用于交换数据、配置Web应用程序环境和表示Web应用程序状态等。

Xml文档的结构很类似于HTML，是由标签组成的。Xml文档需要遵循一定的语法规则，否则解析会出现错误。在Xml解析与更新中，Java提供了自带API和第三方库供我们使用。

使用Java自带API解析XML

在Java中，Xml文档的解析可以使用javax的xml.parsers包下的SAXParser和DocumentBuilder等类，也可以使用org.w3c.dom包下的Document接口等。下面是解析Xml并读取其内容的示例代码：

import org.w3c.dom.Document;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import java.io.InputStream;
import org.xml.sax.InputSource;

public class XmlParser {
    public void parse(InputStream inputStream) throws Exception {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        InputSource inputSource = new InputSource(inputStream);
        Document document = builder.parse(inputSource);
        Element rootElement = document.getDocumentElement();
        NodeList childNodes = rootElement.getChildNodes();
        for (int i = 0; i < childNodes.getLength(); i++) {
            Node node = childNodes.item(i);
            if (node.getNodeType() == Node.ELEMENT_NODE) {
                Element childElement = (Element) node;
                //你的代码逻辑
            }
        }
    }
}

使用第三方库解析XML

除了Java自带的Xml解析API外，我们还可以使用像DOM4J、JDOM、XStream等第三方Xml解析库来解析Xml。这些库都提供了比Java自带API更为易用、更加灵活的Xml解析方式。比如下面是使用DOM4J库来解析Xml的代码示例：

import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
import java.io.InputStream;
import java.util.List;

public class XmlParser {
    public void parse(InputStream inputStream) throws DocumentException {
        SAXReader reader = new SAXReader();
        Document document = reader.read(inputStream);
        Element rootElement = document.getRootElement();
        List<Element> elements = rootElement.elements();
        for (Element element : elements) {
            //你的代码逻辑
        }
    }
}

使用Java自带API更新XML

在Java中，更新Xml文档也可以使用javax.xml.transform包下的Transformer和TransformerFactory类。下面是向Xml文档中添加一个新的节点的示例代码：

import javax.xml.transform.Transformer;
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 java.io.File;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathFactory;

public class XmlUpdater {
    public void update() throws Exception {
        DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
        DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();
        Document document = documentBuilder.parse(new File("example.xml"));
        Element newElement = document.createElement("newNode");
        newElement.appendChild(document.createTextNode("newNode content"));
        XPath xPath = XPathFactory.newInstance().newXPath();
        Element parentNode = (Element) xPath.evaluate("/root", document, XPathConstants.NODE);
        parentNode.appendChild(newElement);
        TransformerFactory transformerFactory = TransformerFactory.newInstance();
        Transformer transformer = transformerFactory.newTransformer();
        DOMSource source = new DOMSource(document);
        StreamResult result = new StreamResult(new File("example.xml"));
        transformer.transform(source, result);
    }
}

使用第三方库更新XML

和解析Xml一样，我们同样可以使用像DOM4J、JDOM、XStream等第三方Xml库来更新Xml文档。比如下面是使用DOM4J库来向Xml文档中添加一个新的节点的示例代码：

import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.DocumentHelper;
import org.dom4j.Element;
import org.dom4j.io.OutputFormat;
import org.dom4j.io.XMLWriter;
import java.io.FileOutputStream;
import java.io.IOException;

public class XmlUpdater {
    public void update() throws IOException, DocumentException {
        Document document = DocumentHelper.createDocument();
        Element rootElement = DocumentHelper.createElement("root");
        document.add(rootElement);
        Element newNode = rootElement.addElement("newNode");
        newNode.setText("newNode content");
        OutputFormat outputFormat = OutputFormat.createPrettyPrint();
        outputFormat.setEncoding("UTF-8");
        XMLWriter xmlWriter = new XMLWriter(new FileOutputStream("example.xml"), outputFormat);
        xmlWriter.write(document);
        xmlWriter.close();
    }
}

示例说明1

假设我们有如下Xml文档：

<?xml version="1.0" encoding="UTF-8"?>
<root>
    <user id="1">
        <name>张三</name>
        <gender>男</gender>
        <age>20</age>
    </user>
    <user id="2">
        <name>李四</name>
        <gender>女</gender>
        <age>25</age>
    </user>
</root>

我们想解析它并读取其中每个user节点中的信息，可以使用像DOM4J、JDOM、XStream等第三方库解析Xml，也可以使用Java自带API解析Xml文档。最终我们可以将解析得到的每个user节点信息打印出来。比如使用Java自带API解析Xml的示例代码：

import org.w3c.dom.Document;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import java.io.InputStream;
import org.xml.sax.InputSource;

public class XmlParser {
    public void parse(InputStream inputStream) throws Exception {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        InputSource inputSource = new InputSource(inputStream);
        Document document = builder.parse(inputSource);
        Element rootElement = document.getDocumentElement();
        NodeList childNodes = rootElement.getChildNodes();
        for (int i = 0; i < childNodes.getLength(); i++) {
            Node node = childNodes.item(i);
            if (node.getNodeType() == Node.ELEMENT_NODE) {
                Element userElement = (Element) node;
                String id = userElement.getAttribute("id");
                String name = userElement.getElementsByTagName("name").item(0).getTextContent();
                String gender = userElement.getElementsByTagName("gender").item(0).getTextContent();
                String age = userElement.getElementsByTagName("age").item(0).getTextContent();
                System.out.println("id: " + id + ", name: " + name + ", gender: " + gender + ", age: " + age);
            }
        }
    }
}

示例说明2

假设我们有如下Xml文档：

<?xml version="1.0" encoding="UTF-8"?>
<root>
    <user id="1">
        <name>张三</name>
        <gender>男</gender>
        <age>20</age>
    </user>
    <user id="2">
        <name>李四</name>
        <gender>女</gender>
        <age>25</age>
    </user>
</root>

我们想向Xml文档中添加一个新的user节点，可以使用像DOM4J、JDOM、XStream等第三方库或Java自带API来更新Xml文档。最终我们可以在Xml文档中添加一个新的user节点。比如使用Java自带API更新Xml的示例代码：

import javax.xml.transform.Transformer;
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 java.io.File;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathFactory;

public class XmlUpdater {
    public void update() throws Exception {
        DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
        DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();
        Document document = documentBuilder.parse(new File("example.xml"));
        Element newUser = document.createElement("user");
        newUser.setAttribute("id", "3");
        Element name = document.createElement("name");
        name.appendChild(document.createTextNode("王五"));
        newUser.appendChild(name);
        Element gender = document.createElement("gender");
        gender.appendChild(document.createTextNode("男"));
        newUser.appendChild(gender);
        Element age = document.createElement("age");
        age.appendChild(document.createTextNode("30"));
        newUser.appendChild(age);
        XPath xPath = XPathFactory.newInstance().newXPath();
        Element parentNode = (Element) xPath.evaluate("/root", document, XPathConstants.NODE);
        parentNode.appendChild(newUser);
        TransformerFactory transformerFactory = TransformerFactory.newInstance();
        Transformer transformer = transformerFactory.newTransformer();
        DOMSource source = new DOMSource(document);
        StreamResult result = new StreamResult(new File("example.xml"));
        transformer.transform(source, result);
    }
}

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基于Java实现XML文件的解析与更新