public class SqlSessionFactoryBuilder {

  //Reader读取mybatis配置文件，传入构造方法
  //除了Reader外，其实还有对应的inputStream作为参数的构造方法，
  //这也体现了mybatis配置的灵活性
  public SqlSessionFactory build(Reader reader) {
    return build(reader, null, null);
  }

  public SqlSessionFactory build(Reader reader, String environment) {
    return build(reader, environment, null);
  }
  
  //mybatis配置文件 + properties, 此时mybatis配置文件中可以不配置properties，也能使用${}形式
  public SqlSessionFactory build(Reader reader, Properties properties) {
    return build(reader, null, properties);
  }
  
  //通过XMLConfigBuilder解析mybatis配置，然后创建SqlSessionFactory对象
  public SqlSessionFactory build(Reader reader, String environment, Properties properties) {
    try {
      XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);
      //下面看看这个方法的源码
      return build(parser.parse());
    } catch (Exception e) {
      throw ExceptionFactory.wrapException("Error building SqlSession.", e);
    } finally {
      ErrorContext.instance().reset();
      try {
        reader.close();
      } catch (IOException e) {
        // Intentionally ignore. Prefer previous error.
      }
    }
  }

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

}