Mybatis源码解析（一）启动及加载

先上一段最简单的加载代码：

public static void main(String[] args) {
        SqlSession sqlSession = null;
        try {
            InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

            // 查询数据库内容
            sqlSession = sqlSessionFactory.openSession();
            User user = sqlSession.selectOne("test.user",1);
            System.out.println(user);

            // 插入数据库内容

        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            if (sqlSession != null) {
                sqlSession.close();
            }
        }
    }

SqlSessionFactory构造：

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

核心配置：Configuration
至于如何生成的Configuration就不展开了，从xml，注解中解析，或者给默认配置项。

再看如何创建一个sqlSession:

DefaultSqlSessionFactory

@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();
    //事务工厂类
    final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
    //事务
    tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
    //执行器
    final Executor executor = configuration.newExecutor(tx, execType);
    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();
  }
}

DefaultSqlSession：执行一个最简单的select操作

@Override
public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
  try {
    MappedStatement ms = configuration.getMappedStatement(statement);
    return executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER);
  } catch (Exception e) {
    throw ExceptionFactory.wrapException("Error querying database.  Cause: " + e, e);
  } finally {
    ErrorContext.instance().reset();
  }
}

其实很简单了，通过executor去执行，具体执行器中怎么执行的，后面再讲。

执行顺序：

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