Java

DOM | SAX | JDOM

详情可参考：Java解析XML方法总结
★₯₰☆ DOM
树模型，支持双向访问和数据修改，占内存

/* parse入参其他形式 eg："cof/11.xml"
* 1. File file = new File(filepath)
* 2. InputStream xmlIns = new FileInputStream(filepath)
* 3. InputSource is = new InputSource(filepath)
* 4. InputStream in = Thread.currentThread().getContextClassLoader().getResourceAsStream(filepath) 
* 5. ByteArrayInputStream bais = new ByteArrayInputStream(xml_str.getBytes())//适应于xml格式字符串 */
public static Document getDocument(String filepath) throws ParserConfigurationException, IOException, SAXException {
	//创建DOM解析器的工厂
	DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
	//DOM解析器对象
	DocumentBuilder builder = factory.newDocumentBuilder();
	//解析XML文档得到整个Document对象
	Document doc = builder.parse(filepath);
	return doc;
}

其中，1-3默认类文件相对路径，getResourceAsStream()默认从ClassPath根下获取，不能以/开头
注意parse()不能直接传xml字符串，否则报错：java.net.MalformedURLException: no protocol

Element root = doc.getDocumentElement();
NodeList list = doc.getElementsByTagName("nodename");

提供参考DocumentBuilderFactory的几个属性设置

factory.setValidating(true);//在文档解析时验证文档
factory.setIgnoringComments(true);//忽略注释
factory.setIgnoringElementContentWhitespace(false);//在解析XML文档时消除元素内容中的空格（“可忽略的空白”）
factory.setCoalescing(false);//将CDATA节点转换为文本节点并将其附加到相邻文本节点

★₯₰☆ SAX
"推"式流模型，事件驱动，无需加载整个xml文档、消耗内存少，但是查询结点需从头遍历，且不支持修改
需重写DefaultHandler接口，实现结点处理方法

public class MySaxHandler extends DefaultHandler {
   @Override
   public void characters(char[] ch, int start, int length) throws SAXException {
      super.characters(ch, start, length);
}}

public static void saxParse(String filepath) throws ParserConfigurationException, SAXException {
    SAXParserFactory factory = SAXParserFactory.newInstance();
    SAXParser sax = factory.newSAXParser();
    sax.parse(filepath, new MySaxHandler());
}

详情自行百度之...

★₯₰☆ JDOM
Java-based Document Object Model，树模型

/* build入参其他形式 eg："cof/11.xml" 
* 1. ByteArrayInputStream bais = new ByteArrayInputStream(xml_str.getBytes())
* 2. File file = new File(filepath)
* 3. InputSource is = new InputSource(new StringReader(xml_str)) */
public static Element getRootElement(String filepath) throws JDOMException, IOException {
    SAXBuilder builder = new SAXBuilder();
    Document doc = builder.build(filepath);
    return doc.getRootElement();
}

注意build()也不能直接传xml字符串，否则报错：java.net.MalformedURLException: no protocol

DOM4J

Document Object Model for Java，采用Java集合框架，并完全支持DOM、SAX，推荐

/* read入参其他形式 eg："cof/11.xml" 
* 其他方式请移步上方 */
public static Document getDocument(String filepath) throws DocumentException {
    SAXReader reader = new SAXReader();
    Document doc = reader.read(filepath);
    return doc;
}

Element root = doc.getRootElement();
Element el = root.element("xxx");
List<Element> list = root.elements("xx");

需引入包：<groupId>org.dom4j</groupId><artifactId>dom4j</artifactId><version>2.1.1</version>
通过结合xpath快速定位元素，默认dom4j不支持，需引入：jaxen-1.1.6

List selectNodes("/xx/aa");
Node selectSingleNode("/xx/aa");
List<Node> selectNodes("/xx/aa/*"); //结点aa的所有子结点

提供部分常用方法：基于dom4j解析xml

public static void createEmptyXmlFile(String xmlPath) {
    Document document = DocumentHelper.createDocument();
	doc2XML(document, xmlPath); //将doc转换为xml文档
}
public static void doc2XML(Document doc, String fileName) {
    OutputFormat format = OutputFormat.createPrettyPrint();
    format.setEncoding("UTF-8");
    XMLWriter writer = null;
    try {
        writer = new XMLWriter(new FileWriter(new File(fileName)), format);
        writer.write(doc);
        writer.close();
    } catch (IOException e) { ... }
}
 

此外，javax.xml.xpath也提供了xpath功能，了解之

XPathFactory factory = XPathFactory.newInstance();
XPath xpath = factory.newXPath();

StAX

Streaming API for XML：XmlStreamReader + XmlStreamWriter，"拉"式流模型，JDK1.6新特性
两套处理XML文档的API：

• 基于指针的API，效率高、抽象化程度低
• 基于事件迭代器的API，效率低、抽象化程序高

InputStream in = XMLParseUtils.getXmlInputStream("filepath");      
XMLInputFactory factory = XMLInputFactory.newFactory();
XMLStreamReader parser = factory.createXMLStreamReader(in);

基于woodstox的StAX2解析XML，参见：高铁直达

Jackson

准备：jackson-core，jackson-dataformat-xml，jackson-databind
参考：jackson序列化xml，jackson快速学习
提供一个xml工具类

public static String jacksonBean2XML(Object obj) throws JsonProcessingException {
    JacksonXmlModule module = new JacksonXmlModule();
    module.setDefaultUseWrapper(false);
    XmlMapper xmlMapper = new XmlMapper(module);
    return xmlMapper.writeValueAsString(obj);
}
public static <T> T jacksonXML2Bean(String xml, Class<T> cls) throws IOException {
    JacksonXmlModule module = new JacksonXmlModule();
    module.setDefaultUseWrapper(false);
    XmlMapper xmlMapper = new XmlMapper(module);
    //自动忽略无法对应pojo的字段
    xmlMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
    return xmlMapper.readValue(xml, cls);
}

注意，要求类T必须要有默认构造方法。
若辅以属性注解，再引入jar包：jackson-annotations，详情请坐高铁
若需格式化输出，要加woodstox-core：high-performance XML processor, implement Stax,SAX2 and Stax2 APIs
相关示例参考：writerWithDefaultPrettyPrinter()