MyBatis源码-解读Executor的三个实现类之ReuseExecutor(重用执行器)

亦凉 2023-02-17 14:53 39阅读 0赞

### 文章目录 ###

*  Pre
 *  Executor 执行器
 *  接口继承关系
 *  ReuseExecutor(重用执行器)
 *   *  入门小demo
     *  源码实现

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmdzaGFuZ3dlaQ_size_16_color_FFFFFF_t_70]

# Pre #

[MyBatis源码-深入理解MyBatis Executor的设计思想][MyBatis_-_MyBatis Executor]

工程部分见  
[MyBatis源码- SqlSession门面模式 & selectList 源码解析][MyBatis_- SqlSession_ _ selectList]

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmdzaGFuZ3dlaQ_size_16_color_FFFFFF_t_70 1]

实际中，我们都是面向SqlSession编程的，不会直接调用Executor来执行业务逻辑，这里我们仅仅是为了深入了解下Executor体系架构才这么搞的，切记。

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# Executor 执行器 #

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmdzaGFuZ3dlaQ_size_16_color_FFFFFF_t_70 2]

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# 接口继承关系 #

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmdzaGFuZ3dlaQ_size_16_color_FFFFFF_t_70 3]

这里我们重点看下Executor的 三个实现子类。

分别是：SimpleExecutor(简单执行器)、ReuseExecutor(重用执行器)、BatchExecutor(批处理执行器)。

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# ReuseExecutor(重用执行器) #

回归下JDBC中的 Statement ， 再和MyBatis 所封装的 对比一下

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmdzaGFuZ3dlaQ_size_16_color_FFFFFF_t_70 4]

PreparedStatement 支持预编译参数

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmdzaGFuZ3dlaQ_size_16_color_FFFFFF_t_70 5]

MyBatis的ReuseExecutor就是利用了JDBC Statement的这个特点 来处理的。

## 入门小demo ##

@Test
        public void testReuseExecutor() throws SQLException { 
            // 通过factory.openSession().getConnection()实例化JdbcTransaction ，用于构建ReuseExecutor
            jdbcTransaction = new JdbcTransaction(factory.openSession().getConnection());
            // 映射SQL
            ms = configuration.getMappedStatement("com.artisan.UserMapper.selectByid");
    
            // 实例化ReuseExecutor
            ReuseExecutor executor = new ReuseExecutor(configuration, jdbcTransaction);
            // 调用doQuery执行查询
            List<User> userList = executor.doQuery(ms, 1, RowBounds.DEFAULT, Executor.NO_RESULT_HANDLER, ms.getBoundSql(1));
            System.out.println(userList.get(0));
    
    
            List<User> userList2 = executor.doQuery(ms, 1, RowBounds.DEFAULT, Executor.NO_RESULT_HANDLER, ms.getBoundSql(1));
            System.out.println(userList2.get(0));
    
        }

执行结果

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmdzaGFuZ3dlaQ_size_16_color_FFFFFF_t_70 6]  
可以看到 相同的SQL语句 会缓存对应的PrepareStatement , 缓存的生命周期： 会话有效期

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## 源码实现 ##

![在这里插入图片描述][20200614182427520.png]

Key 是 sql , Value 是 Statement

执行过程：

executor.doQuery ----> prepareStatement(handler, ms.getStatementLog())

\---------> 见下方源码

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;
      }

先判断本地缓存statementMap是否有数据，有的话从statementMap获取，没有的话建立Statement，并存入本地缓存statementMap 。

注意这个缓存的声明周期 是仅限于本次会话。 会话结束后，这些缓存都会被销毁掉。

区别于SimpleExecutor的实现，多了个本地缓存。 推荐使用ReuseExecutor 。

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[MyBatis_-_MyBatis Executor]: https://artisan.blog.csdn.net/article/details/106560762
[MyBatis_- SqlSession_ _ selectList]: https://artisan.blog.csdn.net/article/details/106740995
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[20200614182427520.png]: https://img-blog.csdnimg.cn/20200614182427520.png