加载到内存中会生成一个对应的MappedStatement对象，然后会以key="com.louis.mybatis.dao.EmployeesMapper.selectByMinSalary" ，value为MappedStatement对象的形式维护到Configuration的一个Map中。当以后需要使用的时候，只需要通过Id值来获取就可以了。

从上述的代码中我们可以看到SqlSession的职能是：SqlSession根据Statement ID, 在mybatis配置对象Configuration中获取到对应的MappedStatement对象，然后调用mybatis执行器来执行具体的操作。

1. MyBatis执行器Executor根据SqlSession传递的参数执行query()方法（由于代码过长，读者只需阅读我注释的地方即可）：

/** 
   * BaseExecutor 类部分代码 
   * 
   */  
public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {
      // 1. 根据具体传入的参数，动态地生成需要执行的SQL语句，用BoundSql对象表示    
      BoundSql boundSql = ms.getBoundSql(parameter);  
      // 2. 为当前的查询创建一个缓存Key  
      CacheKey key = createCacheKey(ms, parameter, rowBounds, boundSql);  
      return query(ms, parameter, rowBounds, resultHandler, key, boundSql);  
}  
 
@SuppressWarnings("unchecked")  
public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {  
       ErrorContext.instance().resource(ms.getResource()).activity("executing a query").object(ms.getId());  
       if (closed) throw new ExecutorException("Executor was closed.");  
       if (queryStack == 0 && ms.isFlushCacheRequired()) {  
           clearLocalCache();  
       }  
       List<E> list;  
       try {  
           queryStack++;  
           list = resultHandler == null ? (List<E>) localCache.getObject(key) : null;  
           if (list != null) {  
               handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);  
           } else {  
               // 3.缓存中没有值，直接从数据库中读取数据    
               list = queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql);  
           }  
       } finally {  
           queryStack--;  
       }  
       if (queryStack == 0) {  
           for (DeferredLoad deferredLoad : deferredLoads) {  
               deferredLoad.load();  
           }  
           deferredLoads.clear(); // issue #601  
           if (configuration.getLocalCacheScope() == LocalCacheScope.STATEMENT) {  
               clearLocalCache(); // issue #482  
           }  
       }  
       return list;  
}

private <E> List<E> queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {  
      List<E> list;  
      localCache.putObject(key, EXECUTION_PLACEHOLDER);  
      try {  
         
          //4. 执行查询，返回List 结果，然后    将查询的结果放入缓存之中  
          list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql);  
      } finally {  
          localCache.removeObject(key);  
      }  
      localCache.putObject(key, list);  
      if (ms.getStatementType() == StatementType.CALLABLE) {  
          localOutputParameterCache.putObject(key, parameter);  
      }  
      return list;  
}