1.项目结构

源码地址：
项目结构：

2. 源码分析

2.1.SqlSessionFactoryBuilder#build(java.io.InputStream)

public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
    try {
      XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
      return build(parser.parse());
    } catch (Exception e) {
      throw ExceptionFactory.wrapException("Error building SqlSession.", e);
    } finally {
      ErrorContext.instance().reset();
      try {
        inputStream.close();
      } catch (IOException e) {
        // Intentionally ignore. Prefer previous error.
      }
    }
  }

1. 创建XMLConfigBuilder对象。Mybatis的xml分为两种，一种是配置文件xml，主要是用来全局配置，比如拦截器、别名、还有mapper文件路径或包名路径等（官网列出了所有的配置属性）。还有一种是Mapper.xml，也是用来声明要执行的Sql，一般会与Mapper接口进行绑定。从名字上来看，XMLConfigBuilder显然就是用来解析第一种xml的对象。
2. XMLConfigBuilder#parse对配置文件进行解析，将解析的数据封装到Configuration对象里面。最终将全局配置Configuration封装DefaultSqlSessionFactory对象里面返回。

2.2 XMLConfigBuilder构造器

public XMLConfigBuilder(InputStream inputStream, String environment, Properties props) {
 this(new XPathParser(inputStream, true, props, new XMLMapperEntityResolver()), environment, props);
}
 
public XPathParser(InputStream inputStream, boolean validation, Properties variables, EntityResolver entityResolver) {
  commonConstructor(validation, variables, entityResolver);
  this.document = createDocument(new InputSource(inputStream));
}

private XMLConfigBuilder(XPathParser parser, String environment, Properties props) {
 super(new Configuration());
  ErrorContext.instance().resource("SQL Mapper Configuration");
  this.configuration.setVariables(props);
  this.parsed = false;
  this.environment = environment;
  this.parser = parser;
}

1. XMLConfigBuilder构造器创建了XPathParser。而XPathParser里面的xpath是通过jdk里面rt.jar实现的，xpath主要是对xml文档进行解析（可以理解为从Document对象中获信息，比如子节点、当前节点的属性等）。在XPathParser对象创建的过程中也调用了XPathParser#createDocument方法，将配置文件流解析成了Document对象。
2. XMLConfigBuilder里面创建了全局的Configuration对象，这个对象在Mybatis整个流程中都被使用

2.3 解析XMLConfigBuilder#parse

public Configuration parse() {
   if (parsed) {
     throw new BuilderException("Each XMLConfigBuilder can only be used once.");
   }
   parsed = true;
   parseConfiguration(parser.evalNode("/configuration"));
   return configuration;
 }

1. XPathParser#evalNode(java.lang.String) 方法通过xpath解析configuration根节点，将解析出的节点信息封装成mybatis的XNode对象，方便后续获取当前节点的属性和子节点的信息。
2. 对文档的节点信息进行解析，封装在全局配置Configuration里面

2.4 解析配置 XMLConfigBuilder#parseConfiguration

private void parseConfiguration(XNode root) {
    try {
      //issue #117 read properties first
      propertiesElement(root.evalNode("properties"));
      Properties settings = settingsAsProperties(root.evalNode("settings"));
      loadCustomVfs(settings);
      loadCustomLogImpl(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);
    }
  }

1. 该方法主要是从XNode中读取config.xml配置，并且将配置封装到全局变量Configuration里面，包含了别名、拦截器、反射工厂、数据源、类型转换器、mapper的资源信息等，这里就不一一说明了。这些配置为后面Sql的执行奠定了基础。
2. 后面会对mapperElement(root.evalNode(“mappers”))方法解析