公司新来一个干练小伙，把 MyBatis 替换成 MyBatis-Plus，上线后哭晕在厕所。。。

2024-02-21码农

大家好，我是鹏磊！

一个老项目，数据库用的是 MySQL 5.7 . 36 ， ORM 框架用的 MyBatis 3.5 . 0 ， mysql-connector-java 版本是 5.1 . 26

新来了一个干练的小伙，精力充沛，看着就是一个喜欢折腾的主

他就觉得 MyBatis 使用起来不够简单，要写的代码还比较多，觉得有必要替换成 MyBatis-Plus

Mybatis-Plus 替换 Mybatis

先准备一张表 tbl_order ，然后初始化 2 条数据

DROP TABLE IF EXISTS tbl_order; CREATE TABLE tbl_order( id bigint(0) UNSIGNED NOT NULL AUTO_INCREMENT COMMENT '自增主键', order_no varchar(50) NOT NULL COMMENT '订单号', pay_time datetime(3) DEFAULT NULL COMMENT '付款时间', created_at datetime(3) NOT NULL DEFAULT CURRENT_TIMESTAMP(3) COMMENT '创建时间', updated_at datetime(3) NOT NULL DEFAULT CURRENT_TIMESTAMP(3) ON UPDATE CURRENT_TIMESTAMP(3) COMMENT '最终修改时间', PRIMARY KEY(id) USING BTREE ) ENGINE = InnoDB COMMENT = '订单'; INSERT INTO tbl_order VALUES(1, '123456', '2024-02-21 18:38:32.000', '2024-02-21 18:37:34.000', '2024-02-21 18:40:01.720'); INSERT INTO tbl_order VALUES(2, '654321', '2024-02-21 19:33:32.000','2024-02-21 19:32:12.020', '2024-02-21 19:34:03.727');

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为了简化演示，我就直接用 Mybatis-Plus 搭建一个示例 demo ，以此来模拟下 "小伙" 替换的过程

只是用 MyBatis-Plus 替换 MyBatis ，其他组件的版本暂不动

Mybatis-Plus 版本就用 "小伙" 引用的版本： 3.1 . 1 ， mysql-connector-java 版本

保持不变还是 5.1 . 26

示例代码：play_it_safe

此时运行 com.qsl.OrderTest#orderListAllTest ，会报错，异常信息如下

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org.springframework.dao.TransientDataAccessResourceException: Error attempting to get column 'pay_time' from result set. Cause: java.sql.SQLException: Conversion not supported for type java.time.LocalDateTime ; Conversion not supported for type java.time.LocalDateTime; nested exception is java.sql.SQLException: Conversion not supported for type java.time.LocalDateTime at org.springframework.jdbc.support.SQLStateSQLExceptionTranslator.doTranslate(SQLStateSQLExceptionTranslator.java:110) at org.springframework.jdbc.support.AbstractFallbackSQLExceptionTranslator.translate(AbstractFallbackSQLExceptionTranslator.java:72) at org.springframework.jdbc.support.AbstractFallbackSQLExceptionTranslator.translate(AbstractFallbackSQLExceptionTranslator.java:81) at org.springframework.jdbc.support.AbstractFallbackSQLExceptionTranslator.translate(AbstractFallbackSQLExceptionTranslator.java:81) at org.mybatis.spring.MyBatisExceptionTranslator.translateExceptionIfPossible(MyBatisExceptionTranslator.java:73) at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:446) at com.sun.proxy.$Proxy53.selectList(Unknown Source) at org.mybatis.spring.SqlSessionTemplate.selectList(SqlSessionTemplate.java:230) at com.baomidou.mybatisplus.core.override.MybatisMapperMethod.executeForMany(MybatisMapperMethod.java:158) at com.baomidou.mybatisplus.core.override.MybatisMapperMethod.execute(MybatisMapperMethod.java:76) at com.baomidou.mybatisplus.core.override.MybatisMapperProxy.invoke(MybatisMapperProxy.java:62) at com.sun.proxy.$Proxy59.selectList(Unknown Source) at com.qsl.OrderTest.orderListAllTest(OrderTest.java:28) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12) at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47) at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17) at org.springframework.test.context.junit4.statements.RunBeforeTestExecutionCallbacks.evaluate(RunBeforeTestExecutionCallbacks.java:74) at org.springframework.test.context.junit4.statements.RunAfterTestExecutionCallbacks.evaluate(RunAfterTestExecutionCallbacks.java:84) at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:75) at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:86) at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:84) at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325) at org.springframework.test.context.junit4.SpringJUnit4 classRunner.runChild(SpringJUnit4 classRunner.java:251) at org.springframework.test.context.junit4.SpringJUnit4 classRunner.runChild(SpringJUnit4 classRunner.java:97) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268) at org.springframework.test.context.junit4.statements.RunBeforeTest classCallbacks.evaluate(RunBeforeTest classCallbacks.java:61) at org.springframework.test.context.junit4.statements.RunAfterTest classCallbacks.evaluate(RunAfterTest classCallbacks.java:70) at org.junit.runners.ParentRunner.run(ParentRunner.java:363) at org.springframework.test.context.junit4.SpringJUnit4 classRunner.run(SpringJUnit4 classRunner.java:190) at org.junit.runner.JUnitCore.run(JUnitCore.java:137) at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69) at com.intellij.rt.junit.IdeaTestRunner$Repeater$1.execute(IdeaTestRunner.java:38) at com.intellij.rt.execution.junit.TestsRepeater.repeat(TestsRepeater.java:11) at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:35) at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:232) at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:55) Caused by: java.sql.SQLException: Conversion not supported for type java.time.LocalDateTime at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1078) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:989) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:975) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:920) at com.mysql.jdbc.ResultSetImpl.getObject(ResultSetImpl.java:5126) at com.mysql.jdbc.JDBC4ResultSet.getObject(JDBC4ResultSet.java:547) at com.mysql.jdbc.ResultSetImpl.getObject(ResultSetImpl.java:5133) at com.zaxxer.hikari.pool.HikariProxyResultSet.getObject(HikariProxyResultSet.java) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.apache.ibatis.logging.jdbc.ResultSetLogger.invoke(ResultSetLogger.java:69) at com.sun.proxy.$Proxy71.getObject(Unknown Source) at org.apache.ibatis.type.LocalDateTimeTypeHandler.getNullableResult(LocalDateTimeTypeHandler.java:38) at org.apache.ibatis.type.LocalDateTimeTypeHandler.getNullableResult(LocalDateTimeTypeHandler.java:28) at org.apache.ibatis.type.BaseTypeHandler.getResult(BaseTypeHandler.java:81) at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.applyAutomaticMappings(DefaultResultSetHandler.java:521) at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.getRowValue(DefaultResultSetHandler.java:402) at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleRowValuesForSimpleResultMap(DefaultResultSetHandler.java:354) at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleRowValues(DefaultResultSetHandler.java:328) at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleResultSet(DefaultResultSetHandler.java:301) at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleResultSets(DefaultResultSetHandler.java:194) at org.apache.ibatis.executor.statement.PreparedStatementHandler.query(PreparedStatementHandler.java:65) at org.apache.ibatis.executor.statement.RoutingStatementHandler.query(RoutingStatementHandler.java:79) at com.baomidou.mybatisplus.core.executor.MybatisSimpleExecutor.doQuery(MybatisSimpleExecutor.java:67) at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:324) at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:156) at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:109) at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:83) at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:147) at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:140) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:433) ... 39 more

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注意看 Caused by

不支持的转换类型：java.time.LocalDateTime

谁不支持？mysql-connector-java 不支持！

那mysql-connector-java 哪个版本支持了，答案是：5.1.37

升级mysql-connector-java

将 mysql-connector-java 升级到 5.1.37 ，再执行下 com.qsl.OrderTest#orderListAllTest

不再报异常，查询结果也正确

MyBatis-Plus 替换 Mybatis 似乎就完成了

顺的让人有点怀疑

Conversion not supported for type java.time.LocalDateTime

我们再回过头去看看前面说到的异常：Conversion not supported for type java.time.LocalDateTime

Mybatis-Plus 替换 MyBatis 之前没这个异常，替换之后就有了这个异常，这不是 Mybatis-Plus 的问题？

如何找这个异常的根因了？

很简单，直接从异常堆栈入手

点了之后，你会发现方法很简单

这么简单的代码能有什么问题？

大家注意看图中左上角 MyBatis 的版本，是 3.5.1 ，并不是最初的 3.5.0

有小伙伴可能会问了：不是用 MyBatis-Plus 替换了 MyBatis 吗，怎么还有 Mybatis ？

这个问题问的真的好，我只想给你个大嘴巴子

你看下 MyBatis-Plus 的官方说明

既然基于 Mybatis 3.5.0 没有抛异常，而基于 3.5.1 抛了异常， LocalDateTimeTypeHandler 在 3.5.1 肯定做了调整

我们来看下调整了什么？

看出什么了？

MyBatis 3.5.0 会处理 LocalDateTime 类型的转换（将 java.sql.Timestamp 转换成 java.time.LocalDateTime ）

然而，注意了，然而来了！！!

然而从 MyBatis 3.5.1 开始，不再处理 LocalDateTime （还包括：LocalDate 、 LocalTime ）类型的转换

而是交由 JDBC 组件，也就是 mysql-connector-java 来实现

而巧的是， mysql-connector-java 5.1.26 不支持类型 LocalDateTime

那它支持哪些类型了？

我们同样从异常堆栈入手

点了之后，可以看到下图

往上滑动鼠标，就可以看到支持的类型了

public <T> T getObject(int columnIndex, class<T> type)throws SQLException { if (type == null) { throw SQLError.createSQLException("Type parameter can not be null", SQLError.SQL_STATE_ILLEGAL_ARGUMENT, getExceptionInterceptor()); } if (type.equals(String. class)) { return (T) getString(columnIndex); } elseif (type.equals(BigDecimal. class)) { return (T) getBigDecimal(columnIndex); } elseif (type.equals(Boolean. class) || type.equals(Boolean.TYPE)) { return (T) Boolean.valueOf(getBoolean(columnIndex)); } elseif (type.equals(Integer. class) || type.equals(Integer.TYPE)) { return (T) Integer.valueOf(getInt(columnIndex)); } elseif (type.equals(Long. class) || type.equals(Long.TYPE)) { return (T) Long.valueOf(getLong(columnIndex)); } elseif (type.equals(Float. class) || type.equals(Float.TYPE)) { return (T) Float.valueOf(getFloat(columnIndex)); } elseif (type.equals(Double. class) || type.equals(Double.TYPE)) { return (T) Double.valueOf(getDouble(columnIndex)); } elseif (type.equals(byte[]. class)) { return (T) getBytes(columnIndex); } elseif (type.equals(java.sql.Date. class)) { return (T) getDate(columnIndex); } elseif (type.equals(Time. class)) { return (T) getTime(columnIndex); } elseif (type.equals(Timestamp. class)) { return (T) getTimestamp(columnIndex); } elseif (type.equals(Clob. class)) { return (T) getClob(columnIndex); } elseif (type.equals(Blob. class)) { return (T) getBlob(columnIndex); } elseif (type.equals(Array. class)) { return (T) getArray(columnIndex); } elseif (type.equals(Ref. class)) { return (T) getRef(columnIndex); } elseif (type.equals(URL. class)) { return (T) getURL(columnIndex); // } else if (type.equals(Struct. class)) { // // } // } else if (type.equals(RowId. class)) { // // } else if (type.equals(NClob. class)) { // // } else if (type.equals(SQLXML. class)) { } else { if (this.connection.getAutoDeserialize()) { try { return (T) getObject(columnIndex); } catch ( classCastException cce) { SQLException sqlEx = SQLError.createSQLException("Conversion not supported for type " + type.getName(), SQLError.SQL_STATE_ILLEGAL_ARGUMENT, getExceptionInterceptor()); sqlEx.initCause(cce); throw sqlEx; } } throw SQLError.createSQLException("Conversion not supported for type " + type.getName(), SQLError.SQL_STATE_ILLEGAL_ARGUMENT, getExceptionInterceptor()); } }