Mybaits源码分析三之XMLConfigBuilder类properties 标签解析

在解析mybatis配置文件中，各个类型的配置顺序依次为

private void parseConfiguration(XNode root) {
    try {
      //issue #117 read properties first
      propertiesElement(root.evalNode("properties"));
      Properties settings = settingsAsProperties(root.evalNode("settings"));
      loadCustomVfs(settings);
      typeAliasesElement(root.evalNode("typeAliases"));
      pluginElement(root.evalNode("plugins"));
      objectFactoryElement(root.evalNode("objectFactory"));
      objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
      reflectorFactoryElement(root.evalNode("reflectorFactory"));
      settingsElement(settings);
      // read it after objectFactory and objectWrapperFactory issue #631
      environmentsElement(root.evalNode("environments"));
      databaseIdProviderElement(root.evalNode("databaseIdProvider"));
      typeHandlerElement(root.evalNode("typeHandlers"));
      mapperElement(root.evalNode("mappers"));
    } catch (Exception e) {
      throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
    }
  }

首先是配置文件加载properties类型的配置 propertiesElement(root.evalNode("properties"));

对应的mybatis配置文件为      

 <properties resource="db.properties">
2      </properties>

等价于 

<properties url="file:///D:workspaceideagitdemo_01srcmain
esourcesdb.properties">
</properties>

两种写法均可以在其中<properties> 标签下可以添加<property>键值对

写法：

<property name="driver" value="com.mysql.cj.jdbc.Driver"/>

针对 propertiesElement(root.evalNode("properties"));方法分析为

private void propertiesElement(XNode context) throws Exception {
  //判断mybatis配置文件是否有properties节点
    if (context != null) {
       //properties节点下的节点,即对应的键值对 
      Properties defaults = context.getChildrenAsProperties();
      //获取对应resource的值，对应这个例子为 db.properties
      String resource = context.getStringAttribute("resource");
      //在properties节点中也可以根据src获取配置文件，需要使用配置文件绝对路径
      String url = context.getStringAttribute("url");
      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.");
      }
      //将对应配置文件中的属性放到Properties类中
      if (resource != null) {
        defaults.putAll(Resources.getResourceAsProperties(resource));
      } else if (url != null) {
        defaults.putAll(Resources.getUrlAsProperties(url));
      }
      //获取Configuration配置，放入到 Properties 对象中
      Properties vars = configuration.getVariables();
      if (vars != null) {
        defaults.putAll(vars);
      }
      //将Properties 对象赋值于xml路径解析中
      parser.setVariables(defaults);
      //将Properties 对象赋值于全局配置Configuration文件中
      configuration.setVariables(defaults);
    }
  }