MyBatis-3.4.2-源码分析1：解析XML之propertiesElement(root.evalNode("properties"))

最新推荐文章于 2024-01-03 08:22:48 发布

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最新推荐文章于 2024-01-03 08:22:48 发布

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文章标签： java 数据库 python

原文链接：https://my.oschina.net/qiangzigege/blog/867307

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上面，拿到了XML文件流，下面开始解析这个文件流。

解析的入口是

public Configuration parse() {
		
		if (parsed) {
			throw new BuilderException("Each XMLConfigBuilder can only be used once.");
		}

		parsed = true;
		// 开始解析XML内容
		parseConfiguration(parser.evalNode("/configuration"));
		return configuration;
	}

public XNode evalNode(String expression) {
		// 从XML文档中抽取expression对应的内容
		return evalNode(document, expression);
	}

Step completed: "thread=main", org.apache.ibatis.parsing.XPathParser.evalNode(), line=217 bci=0
217    		Node node = (Node) evaluate(expression, root, XPathConstants.NODE);

main[1] step
> 
Step completed: "thread=main", org.apache.ibatis.parsing.XPathParser.evaluate(), line=226 bci=0
226    			return xpath.evaluate(expression, root, returnType);

main[1] print xpath
 xpath = "com.sun.org.apache.xpath.internal.jaxp.XPathImpl@3891771e"
main[1] print expression
 expression = "/configuration"
main[1] print root
 root = "[#document: null]"
main[1] print root.getClass()
 root.getClass() = "class com.sun.org.apache.xerces.internal.dom.DeferredDocumentImpl"
main[1]

返回结果

Step completed: "thread=main", org.apache.ibatis.parsing.XPathParser.evalNode(), line=217 bci=9
217    		Node node = (Node) evaluate(expression, root, XPathConstants.NODE);

main[1] step
> 
Step completed: "thread=main", org.apache.ibatis.parsing.XPathParser.evalNode(), line=218 bci=13
218    		if (node == null) {

main[1] print node
 node = "[configuration: null]"
main[1] print node.getClass()
 node.getClass() = "class com.sun.org.apache.xerces.internal.dom.DeferredElementImpl"
main[1]

拿到Configuration之后，第一步就是先执行

propertiesElement(root.evalNode("properties"));

我们来看看里面发生了什么？

public List<XNode> getChildren() {
		//开始
		List<XNode> children = new ArrayList<XNode>();
		//遍历每一个Property节点
		NodeList nodeList = node.getChildNodes();
		if (nodeList != null) {
			for (int i = 0, n = nodeList.getLength(); i < n; i++) {
				Node node = nodeList.item(i);
				//符合条件的话
				if (node.getNodeType() == Node.ELEMENT_NODE) {
					children.add(new XNode(xpathParser, node, variables));
				}
			}
		}
		return children;
		//
	}

children结果如下：

main[1] print children
 children = "[<property name="driver" value="com.mysql.jdbc.Driver"/>
, <property name="url" value="jdbc:mysql://localhost:3306/test1"/>
, <property name="username" value="root"/>
, <property name="password" value="root"/>
]"

---

public Properties getChildrenAsProperties() {
		//看到这里了
		Properties properties = new Properties();
		//开始遍历每一个child节点
		for (XNode child : getChildren()) {
			//取出name & value
			String name = child.getStringAttribute("name");
			String value = child.getStringAttribute("value");
			if (name != null && value != null) {
				//加入到properties中
				properties.setProperty(name, value);
			}
		}
		//返回
		return properties;
	}

最终properties结果为：

Step completed: "thread=main", org.apache.ibatis.parsing.XNode.getChildrenAsProperties(), line=313 bci=76
313        return properties;

main[1] print properties
 properties = "{password=root, url=jdbc:mysql://localhost:3306/test1, driver=com.mysql.jdbc.Driver, username=root}"
main[1]

继续处理

private void propertiesElement(XNode context) throws Exception {
		//看到这里了
		if (context != null) {
			//看到这里了
			Properties defaults = context.getChildrenAsProperties();
			//获取Properties中 resource属性值
			String resource = context.getStringAttribute("resource");
			//获取Properties中 url属性值
			String url = context.getStringAttribute("url");
			//竟然不可以同时存在
			if (resource != null && url != null) {
				throw new BuilderException(
						"The properties element cannot specify both a URL and a resource based property file reference.  Please specify one or the other.");
			}
			//如果resource合法
			if (resource != null) {
				//加入resource对应的属性
				defaults.putAll(Resources.getResourceAsProperties(resource));
			} else if (url != null) {
				defaults.putAll(Resources.getUrlAsProperties(url));
			}
			//合入完毕

还剩下几行没有处理，继续

//合入完毕,还可以从configuration中获取啊...
			Properties vars = configuration.getVariables();
			if (vars != null) {
				defaults.putAll(vars);
			}
			//继续处理
			//回填
			parser.setVariables(defaults);
			//回填
			configuration.setVariables(defaults);
			//结束了

至此，Properties就处理完毕

总结如下：

1)从Properties块重构造
2)插入属性resource的值对应的文件内容
3)Properties vars = configuration.getVariables();
			if (vars != null) {
				defaults.putAll(vars);
			}
依次执行构造内容，然后回填到需要的对象里。

转载于:https://my.oschina.net/qiangzigege/blog/867307