Mybatis框架基础支持层——解析器模块
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解析器模块,核心类XPathParser
/** * 封装了用于xml解析的类XPath、Document和EntityResolver */ public class XPathParser { /** * 将xml文件读入内存,并构建一棵树, * 通过树结构对各个节点node进行操作 */ private Document document; /** * 是否开启xml文本格式验证 */ private boolean validation; /** * 用于加载本地DTD文件 * * 默认情况下,对xml文档进行验证时,会根据xml文件开始 * 位置指定的网址加载对应的dtd或xsd文件,当由于网络原因,易导致验证过慢, * 在实践中往往会提前设置EntityResolver接口对象加载本地的dtd文件, * 从而避免联网加载; * * XMLMapperEntityResolver implement EntityResolver */ private EntityResolver entityResolver; /** * mybatis核心配置文件中标签<properties>定义的键值对 */ private Properties variables; /** * 为查询xml文本而设计的语言,配合Document使用 * XPath之于xml好比Sql之于database */ private XPath xpath; public XPathParser(String xml) { commonConstructor(false, null, null); this.document = createDocument(new InputSource(new StringReader(xml))); } //...一系列构造方法(略) public void setVariables(Properties variables) { this.variables = variables; } /** * XPath提供的一系列eval*()方法用于解析boolean、short、int、String、Node等类型信息, * 通过调用XPath.evaluate()方法查找指定路径的节点或者属性,并进行相应的类型转换 */ public String evalString(String expression) { return evalString(document, expression); } public String evalString(Object root, String expression) { String result = (String) evaluate(expression, root, XPathConstants.STRING); result = PropertyParser.parse(result, variables); return result; } public Boolean evalBoolean(String expression) { return evalBoolean(document, expression); } public Boolean evalBoolean(Object root, String expression) { return (Boolean) evaluate(expression, root, XPathConstants.BOOLEAN); } public Short evalShort(String expression) { return evalShort(document, expression); } public Short evalShort(Object root, String expression) { return Short.valueOf(evalString(root, expression)); } public Integer evalInteger(String expression) { return evalInteger(document, expression); } public Integer evalInteger(Object root, String expression) { return Integer.valueOf(evalString(root, expression)); } public Long evalLong(String expression) { return evalLong(document, expression); } public Long evalLong(Object root, String expression) { return Long.valueOf(evalString(root, expression)); } public Float evalFloat(String expression) { return evalFloat(document, expression); } public Float evalFloat(Object root, String expression) { return Float.valueOf(evalString(root, expression)); } public Double evalDouble(String expression) { return evalDouble(document, expression); } public Double evalDouble(Object root, String expression) { return (Double) evaluate(expression, root, XPathConstants.NUMBER); } public List<XNode> evalNodes(String expression) { return evalNodes(document, expression); } public List<XNode> evalNodes(Object root, String expression) { List<XNode> xnodes = new ArrayList<XNode>(); NodeList nodes = (NodeList) evaluate(expression, root, XPathConstants.NODESET); for (int i = 0; i < nodes.getLength(); i++) { xnodes.add(new XNode(this, nodes.item(i), variables)); } return xnodes; } public XNode evalNode(String expression) { return evalNode(document, expression); } public XNode evalNode(Object root, String expression) { Node node = (Node) evaluate(expression, root, XPathConstants.NODE); if (node == null) { return null; } return new XNode(this, node, variables); } private Object evaluate(String expression, Object root, QName returnType) { try { return xpath.evaluate(expression, root, returnType); } catch (Exception e) { throw new BuilderException("Error evaluating XPath. Cause: " + e, e); } } /** * 创建Dom对象,调用此方法之前必须调用commonConstructor方法完成XPathParser初始化 */ private Document createDocument(InputSource inputSource) { // important: this must only be called AFTER common constructor try { //创建DocumentBuilderFactory对象 DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); /** * 对DocumentBuilderFactory对象进行一系列参数配置 */ factory.setValidating(validation); factory.setNamespaceAware(false); factory.setIgnoringComments(true); factory.setIgnoringElementContentWhitespace(false); factory.setCoalescing(false); factory.setExpandEntityReferences(true); //创建DocumentBuilder对象 DocumentBuilder builder = factory.newDocumentBuilder(); /** * 对DocumentBuilder对象进行一系列参数配置 */ builder.setEntityResolver(entityResolver); builder.setErrorHandler(new ErrorHandler() { @Override public void error(SAXParseException exception) throws SAXException { throw exception; } @Override public void fatalError(SAXParseException exception) throws SAXException { throw exception; } @Override public void warning(SAXParseException exception) throws SAXException { } }); //加载xml文件 return builder.parse(inputSource); } catch (Exception e) { throw new BuilderException("Error creating document instance. Cause: " + e, e); } } /** * 初始化XPathParser */ 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(); } }
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