使用 XML 工具： dom

介绍 java 原始的、不经过封装的 xml 操作方式。

Java 中遵循 w3c（World Wide Web Consortium） 标准实现了各种 dom（Document Object Model，在 org.w3c.dom 包下） 类来抽象描述 XML（Extensible Markup Langurage） 文件。 Java 提供了 javax.xml 包下的各种工具来操作这些 dom 类。

https://github.com/LawssssCat/blog/tree/master/code/demo-java-xml/n01-original-usage/test/java/org/example/

读

XML 文件

<?xml version="1.0" encoding="utf-8" ?>
<my-content>
    <web-site>http://www.example.org</web-site>
    <owner>steven</owner>
    <description>原生 java xml 操作测试消息</description>
    <posts>
        <!-- 我是注释 -->
        <post id="P001">
            <title>文章标题01</title>
            <content>hello world 01！</content>
        </post>
        <post id="P002">
            <title>文章标题02</title>
            <content>hello world 02！</content>
        </post>
    </posts>
</my-content>

测试用例

package org.example;

import lombok.extern.slf4j.Slf4j;
import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.BeforeAll;
import org.junit.jupiter.api.Test;
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.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.xpath.*;
import java.io.IOException;
import java.io.InputStream;

@Slf4j
public class XmlOriginalReadTest {
    static Document document;

    @BeforeAll
    static void initClass() {
        DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
        try {
            DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();
            InputStream resourceAsStream = XmlOriginalReadTest.class.getResourceAsStream("/message001.xml");
            try {
                document = documentBuilder.parse(resourceAsStream);
            } catch (SAXException | IOException e) {
                throw new RuntimeException(e);
            }
        } catch (ParserConfigurationException e) {
            throw new RuntimeException(e);
        }
    }

    /**
     * 测试 dom 基本使用
     */
    @Test
    void test_getElementsByTagName_and_getChildNodes() {
        NodeList posts = document.getElementsByTagName("post");
        Assertions.assertEquals(2, posts.getLength());
        for (int i = 0; i < posts.getLength(); i++) {
            // Element 专指 “标签” 元素
            Element post = (Element) posts.item(i);
            // 👆 Node 实现有： Element Attr Comment Text ...
            log.info("{} class={}", i, post.getClass());
            log.info("{} nodeName={}", i, post.getNodeName());
            log.info("{} attrId={}", i, post.getAttribute("id"));
            NodeList childNodes = post.getChildNodes();
            Assertions.assertEquals(5, childNodes.getLength());
            // 👆 有 5 个子 Node，因为除了 2 个 Element 外，它们中间的空间会被识别成 Text
            // Text Comment（忽略） Text（如入上一个text） Element Text Element Text
            for (int j = 0; j < childNodes.getLength(); j++) {
                Node postDefinition = childNodes.item(j);
                log.info("{}-{} class={}", i, j, postDefinition.getClass());
                if (postDefinition instanceof Element) {
                    log.info("{}-{} nodeName={}", i, j, postDefinition.getNodeName());
                    log.info("{}-{} text={}", i, j, postDefinition.getTextContent());
                    // 💡 获取文本内容，也可以 postDefinition.getFirstChild().getNodeValue()
                }
            }
        }
    }

    /**
     * 测试 xpath 用法
     * 封装： jaxen.jaxen:1.2.0
     */
    @Test
    void test_xpath() {
        XPathFactory xPathFactory = XPathFactory.newInstance();
        XPath xPath = xPathFactory.newXPath();
        try {
            // xpath 语法
            XPathExpression xPathExpression = xPath.compile("//posts//post[@id='P002']//title//text()");
            Node node = (Node) xPathExpression.evaluate(document, XPathConstants.NODE);
            Assertions.assertEquals("文章标题02", node.getNodeValue());
        } catch (XPathExpressionException e) {
            throw new RuntimeException(e);
        }
    }
}

写

测试用例

package org.example;

import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import utils.IOUtils;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.*;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import java.io.File;
import java.io.IOException;
import java.io.OutputStream;
import java.nio.file.Files;
import java.util.Objects;

public class XmlOriginalWriteTest {
    Document document;
    Transformer transformer;
    @BeforeEach
    void initEach() {
        // 格式
        DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
        try {
            DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();
            document = documentBuilder.newDocument();
        } catch (ParserConfigurationException e) {
            throw new RuntimeException(e);
        }
        // 输出
        TransformerFactory transformerFactory = TransformerFactory.newInstance();
        try {
            transformer = transformerFactory.newTransformer();
        } catch (TransformerConfigurationException e) {
            throw new RuntimeException(e);
        }
    }
    @Test
    void test_write() throws IOException {
        // 内容
        Element posts = document.createElement("posts");
        {
            Element post = document.createElement("post");
            post.setTextContent("hello world!");
            post.setAttribute("id", "P001");
            posts.appendChild(post);
        }
        document.appendChild(posts);
        // 输出
        String outputTargetFilename = getClass().getName() + ".xml";
        File outputTargetFile = new File(Objects.requireNonNull(getClass().getResource("/")).getPath(), outputTargetFilename);
        try (OutputStream outputStream = Files.newOutputStream(outputTargetFile.toPath())) {
            try {
                transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8"); // 指定编码
                // transformer.setOutputProperty(OutputKeys.INDENT, "yes"); // 美化输出
                transformer.transform(new DOMSource(document), new StreamResult(outputStream));
            } catch (TransformerException e) {
                throw new RuntimeException(e);
            }
        }
        Assertions.assertTrue(outputTargetFile.exists());
        // validate
        Assertions.assertEquals("<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"no\"?><posts><post id=\"P001\">hello world!</post></posts>",
                IOUtils.readFile(outputTargetFile));
    }
}