StatementHandler接口定义为
Statement prepare(Connection connection, Integer transactionTimeout) throws SQLException; void parameterize(Statement statement) throws SQLException; void batch(Statement statement) throws SQLException; int update(Statement statement) throws SQLException; <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException; <E> Cursor<E> queryCursor(Statement statement) throws SQLException; BoundSql getBoundSql(); ParameterHandler getParameterHandler();类结构图为
RoutingStatementHandler起代理作用，根据不同的语句类型创建不同BaseStatementHandler子类。
PreparedStatementHandler用于处理带有占位符的语句，SimpleStatementHandler处理不带占位符的，CallableStatementHandler处理存储过程调用语句
