MyBatis实现配置加载的步骤

InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

public SqlSessionFactory build(InputStream inputStream) {
    return build(inputStream, null, null);
}

public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
    try {
        // XMLConfigBuilder会解析配置文件并生成Configuration类
        XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
        // 调用入参为Configuration的build()方法构建SqlSessionFactory并返回
        return build(parser.parse());
    } catch (Exception e) {
        throw ExceptionFactory.wrapException("Error building SqlSession.", e);
    } finally {
        ErrorContext.instance().reset();
        try {
            inputStream.close();
        } catch (IOException e) {
        }
    }
}

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

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <settings>
        <setting name="useGeneratedKeys" value="true"/>
    </settings>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/test?characterEncoding=utf-8&amp;serverTimezone=UTC&amp;useSSL=false"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <package name="com.mybatis.learn.dao"/>
    </mappers>
</configuration>

private void parseConfiguration(XNode root) {
    try {
        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);
        // 丰富environments标签及其子标签的属性到Configuration中
        environmentsElement(root.evalNode("environments"));
        databaseIdProviderElement(root.evalNode("databaseIdProvider"));
        typeHandlerElement(root.evalNode("typeHandlers"));
        // 丰富mappers标签的属性到Configuration中
        mapperElement(root.evalNode("mappers"));
    } catch (Exception e) {
        throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);
    }
}

public SqlSessionFactory build(Configuration config) {
    return new DefaultSqlSessionFactory(config);
}