04-MyBatis执行器

MyBatis执行器(Executor)

当构建完成SqlSession后，就需要执行SQL语句，MyBatis中的Executor类是执行引擎的核心，是由它来完成跟数据库的交互。Executor类图如下：

从图中可以看出，Executor主要提供的方法如下：

  • query|update(insert和delete也是使用update)。
  • 事务提交/回滚，委派给Transaction对象来完成。
  • 缓存createCacheKey/isCached/clearLocalCache
  • 提交commit，回滚rollback
    重要方法参数上解释：
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/**
 * 
 * @param ms 存储了一个sql对应的所有信息
 * @param parameter 参数
 * @param rowBounds 分页参数
 * @param resultHandler  结果处理
 * @param boundSql sql信息
 * @param <E>
 * @return
 * @throws SQLException
 */
@Override
public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
  Configuration configuration = ms.getConfiguration();
  StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
  Statement stmt = prepareStatement(handler, ms.getStatementLog());
  return handler.query(stmt, resultHandler);
}

执行器分类

  1. SimpleExecutor(简易执行器)
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@Override
public int doUpdate(MappedStatement ms, Object parameter) throws SQLException {
  Statement stmt = null;
  try {
    Configuration configuration = ms.getConfiguration();
    StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, null, null);
    stmt = prepareStatement(handler, ms.getStatementLog());
    return handler.update(stmt);
  } finally {
    closeStatement(stmt);//关闭Statement
  }
}
private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {
  Statement stmt;
  Connection connection = getConnection(statementLog);
  stmt = handler.prepare(connection, transaction.getTimeout());
  handler.parameterize(stmt);
  return stmt;
}
  1. ReuseExecutor(复用型执行器)
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@Override
public int doUpdate(MappedStatement ms, Object parameter) throws SQLException {
  Configuration configuration = ms.getConfiguration();
  StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, null, null);
  Statement stmt = prepareStatement(handler, ms.getStatementLog());
  return handler.update(stmt);
}
private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {
  Statement stmt;
  BoundSql boundSql = handler.getBoundSql();
  String sql = boundSql.getSql();
  if (hasStatementFor(sql)) {
    stmt = getStatement(sql);
    applyTransactionTimeout(stmt);
  } else {
    Connection connection = getConnection(statementLog);
    stmt = handler.prepare(connection, transaction.getTimeout());
    putStatement(sql, stmt);
  }
  handler.parameterize(stmt);
  return stmt;
}

private boolean hasStatementFor(String sql) {
  try {
    return statementMap.keySet().contains(sql) && !statementMap.get(sql).getConnection().isClosed();
  } catch (SQLException e) {
    return false;
  }
}
  1. BatchExecutor（批处理型执行器）
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@Override
public int doUpdate(MappedStatement ms, Object parameterObject) throws SQLException {
  final Configuration configuration = ms.getConfiguration();
  final StatementHandler handler = configuration.newStatementHandler(this, ms, parameterObject, RowBounds.DEFAULT, null, null);
  final BoundSql boundSql = handler.getBoundSql();
  final String sql = boundSql.getSql();
  final Statement stmt;
  if (sql.equals(currentSql) && ms.equals(currentStatement)) {
    int last = statementList.size() - 1;
    stmt = statementList.get(last);
    applyTransactionTimeout(stmt);
    handler.parameterize(stmt);//fix Issues 322
    BatchResult batchResult = batchResultList.get(last);
    batchResult.addParameterObject(parameterObject);
  } else {
    Connection connection = getConnection(ms.getStatementLog());
    stmt = handler.prepare(connection, transaction.getTimeout());
    handler.parameterize(stmt);    //fix Issues 322
    currentSql = sql;
    currentStatement = ms;
    statementList.add(stmt);
    batchResultList.add(new BatchResult(ms, sql, parameterObject));
  }
  handler.batch(stmt);
  return BATCH_UPDATE_RETURN_VALUE;
}

三种执行器执行对比：

doQuery()

环境准备

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SqlSessionFactory sqlSessionFactory;
MappedStatement ms;
BoundSql boundSql;
Configuration configuration;
Transaction transaction;
DataSource dataSource;
@Before
public void init() throws IOException, SQLException {
    // 读取mybatis核心配置文件
    Reader reader = Resources.getResourceAsReader("mybatis-config.xml");
    // 创建会话工厂
    SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
    sqlSessionFactory = sqlSessionFactoryBuilder.build(reader);

    Configuration configuration = sqlSessionFactory.getConfiguration();
    dataSource = configuration.getEnvironment().getDataSource();
    transaction = configuration.getEnvironment().getTransactionFactory().newTransaction(dataSource.getConnection());
    ms = sqlSessionFactory.getConfiguration().getMappedStatement("com.mybatis.mapper.UserMapper.updateUser");
    boundSql = ms.getBoundSql(1);
}
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SqlSessionFactory sqlSessionFactory;
MappedStatement ms;
BoundSql boundSql;
Configuration configuration;
Transaction transaction;
DataSource dataSource;
@Before
public void init() throws IOException, SQLException {
    // 读取mybatis核心配置文件
    Reader reader = Resources.getResourceAsReader("mybatis-config.xml");
    // 创建会话工厂
    SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
    sqlSessionFactory = sqlSessionFactoryBuilder.build(reader);

    Configuration configuration = sqlSessionFactory.getConfiguration();
    dataSource = configuration.getEnvironment().getDataSource();
    transaction = configuration.getEnvironment().getTransactionFactory().newTransaction(dataSource.getConnection());
    ms = sqlSessionFactory.getConfiguration().getMappedStatement("com.mybatis.mapper.UserMapper.findStudentById");
    boundSql = ms.getBoundSql(1);
}

SimpleExecutor

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@Test
public void SimpleExecutorSelect() throws SQLException {
    SimpleExecutor executor = new SimpleExecutor(configuration, transaction);
    executor.doQuery(ms, 1, RowBounds.DEFAULT, Executor.NO_RESULT_HANDLER, boundSql);
    executor.doQuery(ms, 1, RowBounds.DEFAULT, Executor.NO_RESULT_HANDLER, boundSql);
}
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@Test
public void ReuseExecutorSelect() throws SQLException {
    ReuseExecutor executor = new ReuseExecutor(configuration, transaction);
    executor.doQuery(ms, 1, RowBounds.DEFAULT, Executor.NO_RESULT_HANDLER, boundSql);
    executor.doQuery(ms, 1, RowBounds.DEFAULT, Executor.NO_RESULT_HANDLER, boundSql);

}
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@Test
public void BatchExecutorSelect() throws SQLException {
    BatchExecutor executor = new BatchExecutor(configuration, transaction);
    executor.doQuery(ms, 1, RowBounds.DEFAULT, Executor.NO_RESULT_HANDLER, boundSql);
    executor.doQuery(ms, 1, RowBounds.DEFAULT, Executor.NO_RESULT_HANDLER, boundSql);
}

doUpdate()

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@Test
public void SimpleExecutorUpdate() throws SQLException {
    SimpleExecutor executor = new SimpleExecutor(configuration, transaction);
    User user = new User();
    user.setId("10");
    user.setUsername("2323");
    executor.doUpdate(ms, user);
    executor.doUpdate(ms, user);

}
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@Test
public void ReuseExecutorUpdate() throws SQLException {
    ReuseExecutor executor = new ReuseExecutor(configuration, transaction);
    User user = new User();
    user.setId("10");
    user.setUsername("2323");
    executor.doUpdate(ms, user);
    executor.doUpdate(ms, user);

}
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@Test
public void BatchExecutorUpdate() throws SQLException {
    BatchExecutor executor = new BatchExecutor(configuration, transaction);
    User user = new User();
    user.setId("10");
    user.setUsername("2323");
    executor.doUpdate(ms, user);
    executor.doUpdate(ms, user);
    executor.commit(true);
}

结论：

SimpleExecutor

  • 每条SQL都要进行预处理。
  • 每次只执行一条SQL。

ReuseExecutor

  • 相同SQL只需要预处理一次。
  • 每次只执行一条SQL。

BatchExecutor

  • 每条SQL都要处理一次。
  • 多条SQL可以一次批量执行。
  • 最后一定要调用commit()方法，否则不生效。
编程笔记 MyBatis
源码阅读 MyBatis

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