Mybatis工作机制源码分析—初始化—sax解析

     本文以解析Mybatis config配置文件中"/configuration"元素为例进行说明Mybatis是如何进行sax解析工作的。

Mybatis配置文件解析流程图

时序图

相关源码

/** XMLConfigBuilder.java */// 以解析Mybatis config配置文件"/configuration"元素为例说明sax解析机制：parser.evalNode("/configuration")；/** XPathParser.java */// 解析"/configuration"根节点为XNodepublic XNode evalNode(String expression) {return evalNode(document, expression);}public XNode evalNode(Object root, String expression) {// NODE = new QName("http://www.w3.org/1999/XSL/Transform", "NODE");// 解析"/configuration"根节点为NodeNode node = (Node) evaluate(expression, root, XPathConstants.NODE);if (node == null) {  return null;}// 包装为XNodereturn new XNode(this, node, variables);}// 利用Xpath类解析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);}}/** XPathImpl.java */// XPathImpl解析实现public Object evaluate(String expression, Object item, QName returnType)throws XPathExpressionException {if ( expression == null ) {String fmsg = XSLMessages.createXPATHMessage(XPATHErrorResources.ER_ARG_CANNOT_BE_NULL,new Object[] {"XPath expression"} );throw new NullPointerException ( fmsg );}if ( returnType == null ) {String fmsg = XSLMessages.createXPATHMessage(XPATHErrorResources.ER_ARG_CANNOT_BE_NULL,new Object[] {"returnType"} );throw new NullPointerException ( fmsg );}// Checking if requested returnType is supported. returnType need to// be defined in XPathConstantsif ( !isSupported ( returnType ) ) {String fmsg = XSLMessages.createXPATHMessage(XPATHErrorResources.ER_UNSUPPORTED_RETURN_TYPE,new Object[] { returnType.toString() } );throw new IllegalArgumentException ( fmsg );}try {// Xpath实际解析XObject resultObject = eval( expression, item );// 返回Node节点return getResultAsType( resultObject, returnType );} catch ( java.lang.NullPointerException npe ) {// If VariableResolver returns null Or if we get// NullPointerException at this stage for some other reason// then we have to reurn XPathExceptionthrow new XPathExpressionException ( npe );} catch ( javax.xml.transform.TransformerException te ) {Throwable nestedException = te.getException();if ( nestedException instanceof javax.xml.xpath.XPathFunctionException ) {throw (javax.xml.xpath.XPathFunctionException)nestedException;} else {// For any other exceptions we need to throw// XPathExpressionException ( as per spec )throw new XPathExpressionException ( te );}}}private XObject eval(String expression, Object contextItem)throws javax.xml.transform.TransformerException {// 构造XPathcom.sun.org.apache.xpath.internal.XPath xpath = new com.sun.org.apache.xpath.internal.XPath( expression,null, prefixResolver, com.sun.org.apache.xpath.internal.XPath.SELECT );com.sun.org.apache.xpath.internal.XPathContext xpathSupport = null;if ( functionResolver != null ) {JAXPExtensionsProvider jep = new JAXPExtensionsProvider(functionResolver, featureSecureProcessing, featureManager );xpathSupport = new com.sun.org.apache.xpath.internal.XPathContext( jep );} else {xpathSupport = new com.sun.org.apache.xpath.internal.XPathContext();}XObject xobj = null;xpathSupport.setVarStack(new JAXPVariableStack(variableResolver));// If item is null, then we will create a a Dummy contextNodeif ( contextItem instanceof Node ) {// 实例利用XPath解析xml元素为Node节点xobj = xpath.execute (xpathSupport, (Node)contextItem,prefixResolver );} else {xobj = xpath.execute ( xpathSupport, DTM.NULL, prefixResolver );}return xobj;}// 根据返回的解析类型获取结果private Object getResultAsType( XObject resultObject, QName returnType )throws javax.xml.transform.TransformerException {// XPathConstants.STRINGif ( returnType.equals( XPathConstants.STRING ) ) {return resultObject.str();}// XPathConstants.NUMBERif ( returnType.equals( XPathConstants.NUMBER ) ) {return new Double ( resultObject.num());}// XPathConstants.BOOLEANif ( returnType.equals( XPathConstants.BOOLEAN ) ) {return new Boolean( resultObject.bool());}// XPathConstants.NODESET ---ORdered, UNOrdered???if ( returnType.equals( XPathConstants.NODESET ) ) {return resultObject.nodelist();}// XPathConstants.NODE// 返回Node节点if ( returnType.equals( XPathConstants.NODE ) ) {NodeIterator ni = resultObject.nodeset();//Return the first node, or nullreturn ni.nextNode();}String fmsg = XSLMessages.createXPATHMessage(XPATHErrorResources.ER_UNSUPPORTED_RETURN_TYPE,new Object[] { returnType.toString()});throw new IllegalArgumentException( fmsg );}/** XNode.java */// XNode构造函数public XNode(XPathParser xpathParser, Node node, Properties variables) {this.xpathParser = xpathParser;this.node = node;this.name = node.getNodeName();this.variables = variables;// 获取node节点的属性Propertiesthis.attributes = parseAttributes(node);// 获取node节点的Contentthis.body = parseBody(node);}