MyBatis SQL执行流程与结果映射源码分析-优快云博客

一、MyBatis核心执行流程概述

MyBatis作为一款优秀的ORM框架，其SQL执行流程主要围绕SqlSession、Executor、StatementHandler、ParameterHandler和ResultSetHandler五大核心组件展开。从用户调用Mapper接口方法到最终返回Java对象，整体流程可分为初始化、SQL解析、参数处理、SQL执行和结果映射五个阶段。

二、初始化阶段：构建执行环境

2.1 SqlSessionFactory的创建

MyBatis的入口是SqlSessionFactory，其通过SqlSessionFactoryBuilder解析配置文件（mybatis-config.xml）构建。关键源码位于SqlSessionFactoryBuilder.build()方法：

// SqlSessionFactoryBuilder.java
public SqlSessionFactory build(InputStream inputStream) {
   
   
  return build(inputStream, null, null);
}

public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
   
   
  try {
   
   
    XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
    return build(parser.parse()); // 解析配置文件并构建SqlSessionFactory
  } 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.
    }
  }
}

XMLConfigBuilder.parse() 方法会解析全局配置文件和所有Mapper映射文件，最终生成Configuration对象，包含MyBatis的所有配置信息。

2.2 SqlSession的获取

SqlSession是MyBatis与数据库交互的会话接口，通过SqlSessionFactory获取：

// DefaultSqlSessionFactory.java
@Override
public SqlSession openSession() {
   
   
  return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, false);
}

private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
   
   
  Transaction tx = null;
  try {
   
   
    final Environment environment = configuration.getEnvironment();
    final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
    tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
    final Executor executor = configuration.newExecutor(tx, execType); // 创建Executor
    return new DefaultSqlSession(configuration, executor, autoCommit);
  } catch (Exception e) {
   
   
    closeTransaction(tx); // may have fetched a connection so lets call close()
    throw ExceptionFactory.wrapException("Error opening session.  Cause: " + e, e);
  } finally {
   
   
    ErrorContext.instance().reset();
  }
}