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XPathParser类

news 来源：原创 2024/9/19 10:40:20

XPathParser类是mybatis对 javax.xml.xpath.XPath的包装类。
接下来我们来看下XPathParser类的结构

1、属性

  //  存放读取到的整个XML文档private final Document document;//  是否开启验证private boolean validation;// 自定义的DTD约束文件实体解析器，与validation配合使用private EntityResolver entityResolver;// MyBatis配置文件中的properties节点的信息private Properties variables;//  XPath工具private XPath xpath;

2、构造函数

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 public XPathParser(String xml) {commonConstructor(false, null, null);this.document = createDocument(new InputSource(new StringReader(xml)));}

构造方法包含两部分：

初始化属性

private void commonConstructor(boolean validation, Properties variables, EntityResolver entityResolver) {this.validation = validation;this.entityResolver = entityResolver;this.variables = variables;XPathFactory factory = XPathFactory.newInstance();this.xpath = factory.newXPath();
}

构建XML文档对应的Document

private Document createDocument(InputSource inputSource) {// important: this must only be called AFTER common constructortry {DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();factory.setValidating(validation);factory.setNamespaceAware(false);factory.setIgnoringComments(true);factory.setIgnoringElementContentWhitespace(false);factory.setCoalescing(false);factory.setExpandEntityReferences(true);DocumentBuilder builder = factory.newDocumentBuilder();builder.setEntityResolver(entityResolver);builder.setErrorHandler(new ErrorHandler() {@Overridepublic void error(SAXParseException exception) throws SAXException {throw exception;}@Overridepublic void fatalError(SAXParseException exception) throws SAXException {throw exception;}@Overridepublic void warning(SAXParseException exception) throws SAXException {}});return builder.parse(inputSource);} catch (Exception e) {throw new BuilderException("Error creating document instance.  Cause: " + e, e);}
}

3、方法

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基本类型的解析方法，最终调用的都是方法 evalString(Object root, String expression)

  private Properties variables;private XPath xpath;public String evalString(Object root, String expression) {// 解析结果String result = (String) evaluate(expression, root, XPathConstants.STRING);// 对${}变量从Properties配置文件中进行查找相应的属性值替换,若variables为空或未查找到${}直接返回resultresult = PropertyParser.parse(result, variables);return result;}private Object evaluate(String expression, Object root, QName returnType) {try {// 调用XPath进行解析return xpath.evaluate(expression, root, returnType);} catch (Exception e) {throw new BuilderException("Error evaluating XPath.  Cause: " + e, e);}}

4、总结

可使用XPathParser类来解析自己定义的XML文件，同时也可以仿照mybatis定义自己的Properties文件类替换XML文件中的变量值

        String path = "E:\\GitResource\\springboot-bucket\\springboot-mybatis\\src\\main\\resources\\mapper\\20240729.xml";DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();Document document = documentBuilder.parse(path);XPathParser xPathParser = new XPathParser(document,false,null,null);String evalString = xPathParser.evalString("/mapper/sql[1]");System.out.println(evalString);