公司新來一個幹練小夥，把 MyBatis 替換成 MyBatis-Plus，上線後哭暈在廁所。。。

2024-02-21碼農

大家好，我是鵬磊。

一個老計畫，資料庫用的是 MySQL 5.7 . 36 ， ORM 框架用的 MyBatis 3.5 . 0 ， mysql-connector-java 版本是 5.1 . 26

新來了一個幹練的小夥，精力充沛，看著就是一個喜歡折騰的主

他就覺得 MyBatis 使用起來不夠簡單，要寫的程式碼還比較多，覺得有必要替換成 MyBatis-Plus

Mybatis-Plus 替換 Mybatis

先準備一張表 tbl_order ，然後初始化 2 條數據

DROP TABLE IF EXISTS tbl_order; CREATE TABLE tbl_order( id bigint(0) UNSIGNED NOT NULL AUTO_INCREMENT COMMENT '自增主鍵', order_no varchar(50) NOT NULL COMMENT '訂單號', pay_time datetime(3) DEFAULT NULL COMMENT '付款時間', created_at datetime(3) NOT NULL DEFAULT CURRENT_TIMESTAMP(3) COMMENT '建立時間', updated_at datetime(3) NOT NULL DEFAULT CURRENT_TIMESTAMP(3) ON UPDATE CURRENT_TIMESTAMP(3) COMMENT '最終修改時間', PRIMARY KEY(id) USING BTREE ) ENGINE = InnoDB COMMENT = '訂單'; 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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為了簡化演示，我就直接用 Mybatis-Plus 搭建一個範例 demo ，以此來模擬下 "小夥" 替換的過程

只是用 MyBatis-Plus 替換 MyBatis ，其他元件的版本暫不動

Mybatis-Plus 版本就用 "小夥" 參照的版本： 3.1 . 1 ， mysql-connector-java 版本

保持不變還是 5.1 . 26

範例程式碼：play_it_safe

此時執行 com.qsl.OrderTest#orderListAllTest ，會報錯，異常資訊如下

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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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註意看 Caused by

不支持的轉換型別：java.time.LocalDateTime

誰不支持？mysql-connector-java 不支持！

那mysql-connector-java 哪個版本支持了，答案是：5.1.37

升級mysql-connector-java

將 mysql-connector-java 升級到 5.1.37 ，再執行下 com.qsl.OrderTest#orderListAllTest

不再報異常，查詢結果也正確

MyBatis-Plus 替換 Mybatis 似乎就完成了

順的讓人有點懷疑

Conversion not supported for type java.time.LocalDateTime

我們再回過頭去看看前面說到的異常：Conversion not supported for type java.time.LocalDateTime

Mybatis-Plus 替換 MyBatis 之前沒這個異常，替換之後就有了這個異常，這不是 Mybatis-Plus 的問題？

如何找這個異常的根因了？

很簡單，直接從異常堆疊入手

點了之後，你會發現方法很簡單

這麽簡單的程式碼能有什麽問題？

大家註意看圖中左上角 MyBatis 的版本，是 3.5.1 ，並不是最初的 3.5.0

有小夥伴可能會問了：不是用 MyBatis-Plus 替換了 MyBatis 嗎，怎麽還有 Mybatis ？

這個問題問的真的好，我只想給你個大嘴巴子

你看下 MyBatis-Plus 的官方說明

既然基於 Mybatis 3.5.0 沒有拋異常，而基於 3.5.1 拋了異常， LocalDateTimeTypeHandler 在 3.5.1 肯定做了調整

我們來看下調整了什麽？

看出什麽了？

MyBatis 3.5.0 會處理 LocalDateTime 型別的轉換（將 java.sql.Timestamp 轉換成 java.time.LocalDateTime ）

然而，註意了，然而來了！！!

然而從 MyBatis 3.5.1 開始，不再處理 LocalDateTime （還包括：LocalDate 、 LocalTime ）型別的轉換

而是交由 JDBC 元件，也就是 mysql-connector-java 來實作

而巧的是， mysql-connector-java 5.1.26 不支持型別 LocalDateTime

那它支持哪些型別了？

我們同樣從異常堆疊入手

點了之後，可以看到下圖

往上滑動滑鼠，就可以看到支持的型別了

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()); } }