Java 如何处理 XML 注释和CDATA节

在 Java 中处理 XML 注释和 CDATA 节，可以使用以下方法：

1. 使用 Java 自带的 DOM (Document Object Model) 解析器。

DOM 解析器会将 XML 文档解析为一个树形结构，允许你访问和操作文档的各个部分。要处理 XML 注释和 CDATA 节，你需要遍历 DOM 树并检查节点的类型。

以下是一个简单的示例，演示如何使用 DOM 解析器处理 XML 注释和 CDATA 节：

import org.w3c.dom.*;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import java.io.StringReader;

public class XMLProcessor {
    public static void main(String[] args) throws Exception {
        String xml = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n" +
                "<root>\n" +
                "  <!-- This is a comment -->\n" +
                "  <content><![CDATA[This is a CDATA section]]></content>\n" +
                "</root>";

        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document document = builder.parse(new StringReader(xml));

        processCommentsAndCDATAContent(document);
    }

    private static void processCommentsAndCDATAContent(Document document) {
        // Process comments
        NodeList commentNodes = document.getElementsByTagName("*");
        for (int i = 0; i < commentNodes.getLength(); i++) {
            Node node = commentNodes.item(i);
            if (node.getNodeType() == Node.COMMENT_NODE) {
                System.out.println("Comment: " + node.getTextContent());
            }
        }

        // Process CDATA sections
        NodeList contentNodes = document.getElementsByTagName("content");
        for (int i = 0; i < contentNodes.getLength(); i++) {
            Node node = contentNodes.item(i);
            if (node.getNodeType() == Node.ELEMENT_NODE) {
                Element element = (Element) node;
                String cdataContent = element.getTextContent();
                System.out.println("CDATA content: " + cdataContent);
            }
        }
    }
}

2. 使用第三方库，如 JAXP (Java API for XML Processing) 或 Jackson XML。

这些库提供了更高级的 XML 处理功能，可以更方便地处理注释和 CDATA 节。以下是使用 JAXP 处理 XML 注释和 CDATA 节的示例：

import javax.xml.XMLConstants;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import javax.xml.xpath.*;
import org.w3c.dom.*;
import java.io.StringReader;

public class XMLProcessor {
    public static void main(String[] args) throws Exception {
        String xml = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n" +
                "<root>\n" +
                "  <!-- This is a comment -->\n" +
                "  <content><![CDATA[This is a CDATA section]]></content>\n" +
                "</root>";

        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        factory.setFeature(XMLConstants.FEATURE_PROCESSING_INSTRUCTIONS, true);
        factory.setFeature(XMLConstants.FEATURE_COMMENT_PROCESSING, true);
        factory.setFeature(XMLConstants.FEATURE_CDATA_SECTION_ELEMENTS, "content");

        DocumentBuilder builder = factory.newDocumentBuilder();
        Document document = builder.parse(new StringReader(xml));

        processCommentsAndCDATAContent(document);

        // Output the modified XML
        TransformerFactory transformerFactory = TransformerFactory.newInstance();
        Transformer transformer = transformerFactory.newTransformer();
        transformer.setOutputProperty(OutputKeys.INDENT, "yes");
        DOMSource source = new DOMSource(document);
        StreamResult result = new StreamResult(System.out);
        transformer.transform(source, result);
    }

    private static void processCommentsAndCDATAContent(Document document) {
        // Process comments
        XPathFactory xPathFactory = XPathFactory.newInstance();
        XPath xpath = xPathFactory.newXPath();
        NodeList commentNodes = (NodeList) xpath.evaluate("//comment()", document, XPathConstants.NODESET);
        for (int i = 0; i < commentNodes.getLength(); i++) {
            System.out.println("Comment: " + commentNodes.item(i).getTextContent());
        }

        // Process CDATA sections
        NodeList contentNodes = (NodeList) xpath.evaluate("//content", document, XPathConstants.NODESET);
        for (int i = 0; i < contentNodes.getLength(); i++) {
            System.out.println("CDATA content: " + contentNodes.item(i).getTextContent());
        }
    }
}

这个示例使用了 JAXP 的 XPath 支持来查找和输出注释和 CDATA 节的内容。注意，要使用 JAXP，你需要将其添加到项目的依赖项中。如果你使用 Maven，可以在 pom.xml 文件中添加以下依赖：

<dependency>
    <groupId>javax.xml.parsers</groupId>
    <artifactId>jaxb-api</artifactId>
    <version>2.3.1</version>
</dependency>
<dependency>
    <groupId>org.glassfish.jaxb</groupId>
    <artifactId>jaxb-runtime</artifactId>
    <version>2.3.1</version>
</dependency>
<dependency>
    <groupId>org.glassfish.jaxb</groupId>
    <artifactId>jaxb-xjc</artifactId>
    <version>2.3.1</version>
</dependency>
<dependency>
    <groupId>com.sun.xml.bind</groupId>
    <artifactId>jaxb-core</artifactId>
    <version>2.3.1</version>
</dependency>
<dependency>
    <groupId>javax.activation</groupId>
    <artifactId>activation</artifactId>
    <version>1.1.1</version>
</dependency>