開心一刻
今天，老婆給我發訊息
老婆：老公，兒子從隔壁鄰居家回來了
老婆：是先打還是先洗？
我：先洗吧，萬一打錯人了呢
老婆：先洗臉吧，沒錯就邊打邊洗
起因
在我們的固有認知中， mysql-connector-java-5.x.x 連線的是 MySQL5 ，而 mysql-connector-java-8.x.x 連線的是 MySQL8
如果用 mysql-connector-java-5.x.x 連線 MySQL8 ，或者用 mysql-connector-java-8.x.x 連線 MySQL5 ，會出問題
至於出什麼問題，呃...，我沒想過，也沒試過，我相信你們也是一樣的
但無意間，我嘗試了下，確實有問題
一開始，我的一個 demo 是基於 MySQL 5.7.36 、 mysql-connector-java 5.1.26 、 MyBatis-Plus 3.1.0
示例程式碼：play_it_safe
因為 MySQL 5.7.36 被我刪了，而本機（ windows 10 ）上正好有 MySQL 8.0.26
那就用 MySQL 8.0.26 來跑 demo 唄，只修改資料庫連線的 url 、 username 和 password
然後就出現了一系列的異常
java.math.BigInteger cannot be cast to java.lang.Long
啟動直接異常
java.sql.SQLException: java.lang.ClassCastException: java.math.BigInteger cannot be cast to java.lang.Long at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1078) ~[mysql-connector-java-5.1.26.jar:na] at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:989) ~[mysql-connector-java-5.1.26.jar:na] at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:975) ~[mysql-connector-java-5.1.26.jar:na] at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:920) ~[mysql-connector-java-5.1.26.jar:na] at com.mysql.jdbc.ConnectionImpl.buildCollationMapping(ConnectionImpl.java:1074) ~[mysql-connector-java-5.1.26.jar:na] at com.mysql.jdbc.ConnectionImpl.initializePropsFromServer(ConnectionImpl.java:3593) ~[mysql-connector-java-5.1.26.jar:na] at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2534) ~[mysql-connector-java-5.1.26.jar:na] at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2304) ~[mysql-connector-java-5.1.26.jar:na] at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:834) ~[mysql-connector-java-5.1.26.jar:na] at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47) ~[mysql-connector-java-5.1.26.jar:na] at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:1.8.0_91] at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) ~[na:1.8.0_91] at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:1.8.0_91] at java.lang.reflect.Constructor.newInstance(Constructor.java:423) ~[na:1.8.0_91] at com.mysql.jdbc.Util.handleNewInstance(Util.java:411) ~[mysql-connector-java-5.1.26.jar:na] at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:416) ~[mysql-connector-java-5.1.26.jar:na] at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:346) ~[mysql-connector-java-5.1.26.jar:na] at com.zaxxer.hikari.util.DriverDataSource.getConnection(DriverDataSource.java:138) ~[HikariCP-3.4.5.jar:na] at com.zaxxer.hikari.pool.PoolBase.newConnection(PoolBase.java:358) ~[HikariCP-3.4.5.jar:na] at com.zaxxer.hikari.pool.PoolBase.newPoolEntry(PoolBase.java:206) ~[HikariCP-3.4.5.jar:na] at com.zaxxer.hikari.pool.HikariPool.createPoolEntry(HikariPool.java:477) [HikariCP-3.4.5.jar:na] at com.zaxxer.hikari.pool.HikariPool.checkFailFast(HikariPool.java:560) [HikariCP-3.4.5.jar:na] at com.zaxxer.hikari.pool.HikariPool.<init>(HikariPool.java:115) [HikariCP-3.4.5.jar:na] at com.zaxxer.hikari.HikariDataSource.getConnection(HikariDataSource.java:112) [HikariCP-3.4.5.jar:na] at com.baomidou.mybatisplus.extension.spring.MybatisSqlSessionFactoryBean.buildSqlSessionFactory(MybatisSqlSessionFactoryBean.java:486) [mybatis-plus-extension-3.1.1.jar:3.1.1] at com.baomidou.mybatisplus.extension.spring.MybatisSqlSessionFactoryBean.afterPropertiesSet(MybatisSqlSessionFactoryBean.java:434) [mybatis-plus-extension-3.1.1.jar:3.1.1] at com.baomidou.mybatisplus.extension.spring.MybatisSqlSessionFactoryBean.getObject(MybatisSqlSessionFactoryBean.java:633) [mybatis-plus-extension-3.1.1.jar:3.1.1] at com.baomidou.mybatisplus.autoconfigure.MybatisPlusAutoConfiguration.sqlSessionFactory(MybatisPlusAutoConfiguration.java:190) [mybatis-plus-boot-starter-3.1.1.jar:3.1.1] at com.baomidou.mybatisplus.autoconfigure.MybatisPlusAutoConfiguration$$EnhancerBySpringCGLIB$$8802fc19.CGLIB$sqlSessionFactory$1(<generated>) [mybatis-plus-boot-starter-3.1.1.jar:3.1.1] at com.baomidou.mybatisplus.autoconfigure.MybatisPlusAutoConfiguration$$EnhancerBySpringCGLIB$$8802fc19$$FastClassBySpringCGLIB$$f9d1deeb.invoke(<generated>) [mybatis-plus-boot-starter-3.1.1.jar:3.1.1] at org.springframework.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:244) [spring-core-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.context.annotation.ConfigurationClassEnhancer$BeanMethodInterceptor.intercept(ConfigurationClassEnhancer.java:331) [spring-context-5.2.9.RELEASE.jar:5.2.9.RELEASE] at com.baomidou.mybatisplus.autoconfigure.MybatisPlusAutoConfiguration$$EnhancerBySpringCGLIB$$8802fc19.sqlSessionFactory(<generated>) [mybatis-plus-boot-starter-3.1.1.jar:3.1.1] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_91] at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_91] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_91] at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_91] at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:154) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.ConstructorResolver.instantiate(ConstructorResolver.java:650) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:635) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1336) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1176) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:556) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:516) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:324) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:322) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:276) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1307) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1227) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireByType(AbstractAutowireCapableBeanFactory.java:1509) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1404) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:593) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:516) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:324) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:322) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:878) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:879) ~[spring-context-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:551) ~[spring-context-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:141) ~[spring-boot-2.2.10.RELEASE.jar:2.2.10.RELEASE] at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:747) ~[spring-boot-2.2.10.RELEASE.jar:2.2.10.RELEASE] at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397) ~[spring-boot-2.2.10.RELEASE.jar:2.2.10.RELEASE] at org.springframework.boot.SpringApplication.run(SpringApplication.java:315) ~[spring-boot-2.2.10.RELEASE.jar:2.2.10.RELEASE] at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226) ~[spring-boot-2.2.10.RELEASE.jar:2.2.10.RELEASE] at org.springframework.boot.SpringApplication.run(SpringApplication.java:1215) ~[spring-boot-2.2.10.RELEASE.jar:2.2.10.RELEASE] at com.qsl.PlayItSafeApplication.main(PlayItSafeApplication.java:16) ~[classes/:na] Caused by: java.lang.ClassCastException: java.math.BigInteger cannot be cast to java.lang.Long at com.mysql.jdbc.ConnectionImpl.buildCollationMapping(ConnectionImpl.java:1019) ~[mysql-connector-java-5.1.26.jar:na] ... 64 common frames omitted
這確實出乎了我的意料，我認為的是：啟動不會異常，執行中出現異常
既然異常來了，那就好好看看唄
怎麼看？直接從異常堆疊中看，找到 Caused by
直接點選框住的，來到 mysql-connector-java 5.1.26 的原始碼
這個 for 迴圈遍歷的是 sortedCollationMap ， indexEntry 則表示遍歷的當前元素
我問個問題： java.math.BigInteger cannot be cast to java.lang.Long 異常是誰丟擲來的， getKey() 還是 intValue() ？
很簡單，用排除法嘛
Long 是有 intValue() 方法的，只會 NPE ，不會 java.math.BigInteger cannot be cast to java.lang.Long
那就是 getKey() 丟擲的異常唄，我們猜想下什麼情況會丟擲這個異常
indexEntry 宣告的型別雖然是 Map.Entry<Long, String> ，但實際它的 key 不是 Long 型別，而是 BigInteger 型別？
再往上追溯一下， sortedCollationMap 宣告的型別是 TreeMap<Long, String> ，但實際存放元素的 key 是 BigInteger 型別？
此時你們對這個猜想肯定有疑問：這編譯不會報錯嗎
直接 put 是會編譯報錯的，但是如果我變通下呢
編譯沒問題，但是執行會有如下異常
同樣也是 int collationIndex = entry.getKey().intValue(); 丟擲的異常
但兩者原因是否一致，我們還需要對 play_it_safe 驗證
如何驗證， debug 除錯唄
斷點不能打在 connectionimpl.java:1019 這一行，因為此時是遍歷 sortedCollationMap ，而非往裡面 put 元素
我們需要看，往 sortedCollationMap 裡面 put 的 key 具體是什麼型別，所以斷點打在 1002 行
會走 if 分支
F7 跟進去
key 的型別就是 BigInteger ，證明我們的猜想是對的！
但是大家別高興的太早，根因還沒找到，我們得繼續跟進 com.mysql.jdbc.ResultSetImpl#getObject(int)
重點看這個 switch
繼續跟進，你會發現來到 BIGINT 分支
注意，重點來了
這段程式碼很簡單，相信大家都能看到，但我還是分 3 塊給大家說明下
1、 unsigned 表示無符號，然後再取反則表示有符號，也就是說如果資料庫欄位型別是有符號的 bigint ，則用 java.lang.Long 接收欄位值並返回
2、如果資料庫欄位型別是無符號的 bigint ，則用 java.lang.String 來接收欄位值，如果值為 null 則直接返回 null
3、如果資料庫欄位型別是無符號的 bigint ，並且欄位值不是 null ，則用 java.math.BigInteger 來接收欄位值並返回
此刻相信大家對異常的根因有點明白了，但又沒有完全明白，為什麼了？
因為沒有弄清楚來龍去脈，我給大家捋一下：
1、程式啟動過程（初始化）中，mysql-connector-java 5.1.26 會構建欄位級字符集/字元序到java字元編碼名稱的對映
也就是會執行 com.mysql.jdbc.ConnectionImpl#buildCollationMapping 方法
2、 buildCollationMapping 方法中會執行 SQL SHOW COLLATION 來獲取 MySQL 的字符集和字元序
Id：字元序id
Charset：字符集名稱
關於 MySQL 的字符集和字元序的更多資訊，可檢視記一次字串末尾空白丟失的排查 → MySQL 是會玩的！
3、從查詢結果集中，逐行取第 3 列（ Id ）作為 key ，取第 2 列（ Charset ）作為 value ， put 到 sortedCollationMap 中
對應程式碼就是： Util.resultSetToMap(sortedCollationMap, results, 3, 2);
4、在取 Id 列值的時候，會根據資料庫列型別，用不同的 java 型別來接收列值
MySQL 8.0.26 中， COLLATIONS 表的 ID 列的型別是 bigint unsigned
那麼用什麼 java 型別來接收？往上面翻一翻，是不是用 java.math.BigInteger 來接收？
MySQL 5.7.36 中， COLLATIONS 表的 ID 列的型別卻是 bigint(11)
所以用 java.lang.Long 來接收
5、 for 迴圈遍歷 sortedCollationMap ，完成資料庫欄位級字符集/字元序到java字元編碼名稱的對映
indexEntry.getKey() 在 MySQL 8.0.26 會丟擲異常： java.math.BigInteger cannot be cast to java.lang.Long
而在 MySQL 5.7.36 則正常，不丟擲異常
至此，大家對根因是不是完全明白了？
說的簡單點就是： mysql-connector-java 5.1.26 配不上 MySQL 8 ！
說的詳細點就是： mysql-connector-java 5.1.26 適配的是 COLLATIONS 的 bigint 型別的 ID ，而非 bigint unsigned 型別的 ID
說的抽象點就是：上岸第一劍 先斬意中人， MySQL 從 5 上岸到了 8， mysql-connector-java 如果不跟著上岸的話，會被第一個斬殺
Unknown system variable 'query_cache_size'
因為用的是都說了能不動就別動，非要去調整，出生產事故了吧中的 demo ：play_it_safe
所以我順手將 mysql-connector-java 調整到了 5.1.37 ， MySQL 還是 8.0.26 ，結果啟動出現了另一個異常
java.sql.SQLException: Unknown system variable 'query_cache_size' at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:959) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3870) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3806) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2470) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2617) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2546) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2504) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.StatementImpl.executeQuery(StatementImpl.java:1370) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.ConnectionImpl.loadServerVariables(ConnectionImpl.java:3861) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.ConnectionImpl.initializePropsFromServer(ConnectionImpl.java:3289) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2298) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2084) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:795) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:44) ~[mysql-connector-java-5.1.37.jar:5.1.37] at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:1.8.0_91] at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) ~[na:1.8.0_91] at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:1.8.0_91] at java.lang.reflect.Constructor.newInstance(Constructor.java:423) ~[na:1.8.0_91] at com.mysql.jdbc.Util.handleNewInstance(Util.java:404) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:400) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:327) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.zaxxer.hikari.util.DriverDataSource.getConnection(DriverDataSource.java:138) ~[HikariCP-3.4.5.jar:na] at com.zaxxer.hikari.pool.PoolBase.newConnection(PoolBase.java:358) ~[HikariCP-3.4.5.jar:na] at com.zaxxer.hikari.pool.PoolBase.newPoolEntry(PoolBase.java:206) ~[HikariCP-3.4.5.jar:na] at com.zaxxer.hikari.pool.HikariPool.createPoolEntry(HikariPool.java:477) [HikariCP-3.4.5.jar:na] at com.zaxxer.hikari.pool.HikariPool.checkFailFast(HikariPool.java:560) [HikariCP-3.4.5.jar:na] at com.zaxxer.hikari.pool.HikariPool.<init>(HikariPool.java:115) [HikariCP-3.4.5.jar:na] at com.zaxxer.hikari.HikariDataSource.getConnection(HikariDataSource.java:112) [HikariCP-3.4.5.jar:na] at com.baomidou.mybatisplus.extension.spring.MybatisSqlSessionFactoryBean.buildSqlSessionFactory(MybatisSqlSessionFactoryBean.java:591) [mybatis-plus-extension-3.1.0.jar:3.1.0] at com.baomidou.mybatisplus.extension.spring.MybatisSqlSessionFactoryBean.afterPropertiesSet(MybatisSqlSessionFactoryBean.java:422) [mybatis-plus-extension-3.1.0.jar:3.1.0] at com.baomidou.mybatisplus.extension.spring.MybatisSqlSessionFactoryBean.getObject(MybatisSqlSessionFactoryBean.java:636) [mybatis-plus-extension-3.1.0.jar:3.1.0] at com.baomidou.mybatisplus.autoconfigure.MybatisPlusAutoConfiguration.sqlSessionFactory(MybatisPlusAutoConfiguration.java:172) [mybatis-plus-boot-starter-3.1.0.jar:3.1.0] at com.baomidou.mybatisplus.autoconfigure.MybatisPlusAutoConfiguration$$EnhancerBySpringCGLIB$$eeb10e55.CGLIB$sqlSessionFactory$2(<generated>) [mybatis-plus-boot-starter-3.1.0.jar:3.1.0] at com.baomidou.mybatisplus.autoconfigure.MybatisPlusAutoConfiguration$$EnhancerBySpringCGLIB$$eeb10e55$$FastClassBySpringCGLIB$$de0ae008.invoke(<generated>) [mybatis-plus-boot-starter-3.1.0.jar:3.1.0] at org.springframework.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:244) [spring-core-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.context.annotation.ConfigurationClassEnhancer$BeanMethodInterceptor.intercept(ConfigurationClassEnhancer.java:331) [spring-context-5.2.9.RELEASE.jar:5.2.9.RELEASE] at com.baomidou.mybatisplus.autoconfigure.MybatisPlusAutoConfiguration$$EnhancerBySpringCGLIB$$eeb10e55.sqlSessionFactory(<generated>) [mybatis-plus-boot-starter-3.1.0.jar:3.1.0] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_91] at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_91] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_91] at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_91] at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:154) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.ConstructorResolver.instantiate(ConstructorResolver.java:650) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:635) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1336) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1176) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:556) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:516) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:324) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:322) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:276) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1307) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1227) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireByType(AbstractAutowireCapableBeanFactory.java:1509) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1404) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:593) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:516) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:324) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:322) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:878) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:879) ~[spring-context-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:551) ~[spring-context-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:141) ~[spring-boot-2.2.10.RELEASE.jar:2.2.10.RELEASE] at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:747) ~[spring-boot-2.2.10.RELEASE.jar:2.2.10.RELEASE] at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397) ~[spring-boot-2.2.10.RELEASE.jar:2.2.10.RELEASE] at org.springframework.boot.SpringApplication.run(SpringApplication.java:315) ~[spring-boot-2.2.10.RELEASE.jar:2.2.10.RELEASE] at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226) ~[spring-boot-2.2.10.RELEASE.jar:2.2.10.RELEASE] at org.springframework.boot.SpringApplication.run(SpringApplication.java:1215) ~[spring-boot-2.2.10.RELEASE.jar:2.2.10.RELEASE] at com.qsl.PlayItSafeApplication.main(PlayItSafeApplication.java:16) ~[classes/:na]
看到這個異常，不知道你們第一反應想到的是什麼？
我第一反應想到的是 MySQL 8 取消了查詢快取，而 MySQL 5 是有查詢快取的
異常提示的已經很明顯了，我們來驗證下
MySQL 5.7.36 是有系統變數 query_cache_size
而 MySQL 8.0.26 是沒有的
後面我又將 mysql-connector-java 升級到 5.1.42 ，啟動還是異常： Unknown system variable 'query_cache_size'
Could not create connection to database server
因為需要用 MySQL 5.7.36 做對比，所以還是 Docker 快速安裝了一個 MySQL 5.7.36
順帶也安裝了 MySQL 8.0.26 （前面用的是 Win10 版，這個相當於是 Linux 版本）
然後我又鬼使神差的將連線調整到了 Linux 版的 MySQL 8.0.26
當 mysql-connector-java 是 5.1.42 時，啟動異常是： Unknown system variable 'query_cache_size'
當 mysql-connector-java 是 5.1.37 時，啟動異常是： Could not create connection to database server
com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Could not create connection to database server. at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:1.8.0_91] at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) ~[na:1.8.0_91] at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:1.8.0_91] at java.lang.reflect.Constructor.newInstance(Constructor.java:423) ~[na:1.8.0_91] at com.mysql.jdbc.Util.handleNewInstance(Util.java:404) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.Util.getInstance(Util.java:387) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:919) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:898) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:887) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:862) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2331) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2084) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:795) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:44) ~[mysql-connector-java-5.1.37.jar:5.1.37] at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:1.8.0_91] at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) ~[na:1.8.0_91] at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:1.8.0_91] at java.lang.reflect.Constructor.newInstance(Constructor.java:423) ~[na:1.8.0_91] at com.mysql.jdbc.Util.handleNewInstance(Util.java:404) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:400) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:327) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.zaxxer.hikari.util.DriverDataSource.getConnection(DriverDataSource.java:138) ~[HikariCP-3.4.5.jar:na] at com.zaxxer.hikari.pool.PoolBase.newConnection(PoolBase.java:358) ~[HikariCP-3.4.5.jar:na] at com.zaxxer.hikari.pool.PoolBase.newPoolEntry(PoolBase.java:206) ~[HikariCP-3.4.5.jar:na] at com.zaxxer.hikari.pool.HikariPool.createPoolEntry(HikariPool.java:477) [HikariCP-3.4.5.jar:na] at com.zaxxer.hikari.pool.HikariPool.checkFailFast(HikariPool.java:560) [HikariCP-3.4.5.jar:na] at com.zaxxer.hikari.pool.HikariPool.<init>(HikariPool.java:115) [HikariCP-3.4.5.jar:na] at com.zaxxer.hikari.HikariDataSource.getConnection(HikariDataSource.java:112) [HikariCP-3.4.5.jar:na] at com.baomidou.mybatisplus.extension.spring.MybatisSqlSessionFactoryBean.buildSqlSessionFactory(MybatisSqlSessionFactoryBean.java:591) [mybatis-plus-extension-3.1.0.jar:3.1.0] at com.baomidou.mybatisplus.extension.spring.MybatisSqlSessionFactoryBean.afterPropertiesSet(MybatisSqlSessionFactoryBean.java:422) [mybatis-plus-extension-3.1.0.jar:3.1.0] at com.baomidou.mybatisplus.extension.spring.MybatisSqlSessionFactoryBean.getObject(MybatisSqlSessionFactoryBean.java:636) [mybatis-plus-extension-3.1.0.jar:3.1.0] at com.baomidou.mybatisplus.autoconfigure.MybatisPlusAutoConfiguration.sqlSessionFactory(MybatisPlusAutoConfiguration.java:172) [mybatis-plus-boot-starter-3.1.0.jar:3.1.0] at com.baomidou.mybatisplus.autoconfigure.MybatisPlusAutoConfiguration$$EnhancerBySpringCGLIB$$b0a04890.CGLIB$sqlSessionFactory$2(<generated>) [mybatis-plus-boot-starter-3.1.0.jar:3.1.0] at com.baomidou.mybatisplus.autoconfigure.MybatisPlusAutoConfiguration$$EnhancerBySpringCGLIB$$b0a04890$$FastClassBySpringCGLIB$$b0fb4ddc.invoke(<generated>) [mybatis-plus-boot-starter-3.1.0.jar:3.1.0] at org.springframework.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:244) [spring-core-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.context.annotation.ConfigurationClassEnhancer$BeanMethodInterceptor.intercept(ConfigurationClassEnhancer.java:331) [spring-context-5.2.9.RELEASE.jar:5.2.9.RELEASE] at com.baomidou.mybatisplus.autoconfigure.MybatisPlusAutoConfiguration$$EnhancerBySpringCGLIB$$b0a04890.sqlSessionFactory(<generated>) [mybatis-plus-boot-starter-3.1.0.jar:3.1.0] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_91] at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_91] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_91] at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_91] at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:154) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.ConstructorResolver.instantiate(ConstructorResolver.java:650) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:635) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1336) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1176) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:556) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:516) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:324) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:322) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:276) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1307) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1227) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireByType(AbstractAutowireCapableBeanFactory.java:1509) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1404) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:593) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:516) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:324) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:322) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:878) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:879) ~[spring-context-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:551) ~[spring-context-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:141) ~[spring-boot-2.2.10.RELEASE.jar:2.2.10.RELEASE] at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:747) ~[spring-boot-2.2.10.RELEASE.jar:2.2.10.RELEASE] at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397) ~[spring-boot-2.2.10.RELEASE.jar:2.2.10.RELEASE] at org.springframework.boot.SpringApplication.run(SpringApplication.java:315) ~[spring-boot-2.2.10.RELEASE.jar:2.2.10.RELEASE] at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226) ~[spring-boot-2.2.10.RELEASE.jar:2.2.10.RELEASE] at org.springframework.boot.SpringApplication.run(SpringApplication.java:1215) ~[spring-boot-2.2.10.RELEASE.jar:2.2.10.RELEASE] at com.qsl.PlayItSafeApplication.main(PlayItSafeApplication.java:16) ~[classes/:na] Caused by: java.lang.NullPointerException: null at com.mysql.jdbc.ConnectionImpl.getServerCharset(ConnectionImpl.java:3004) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.MysqlIO.sendConnectionAttributes(MysqlIO.java:1908) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.MysqlIO.proceedHandshakeWithPluggableAuthentication(MysqlIO.java:1837) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1207) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2254) ~[mysql-connector-java-5.1.37.jar:5.1.37] at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2285) ~[mysql-connector-java-5.1.37.jar:5.1.37] ... 62 common frames omitted
關鍵異常堆疊是：
真正的異常其實是 NPE ，大家可以參考前面講到的方法去分析
當 mysql-connector-java 是 5.1.26 時，啟動異常也是： Could not create connection to database server
com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Could not create connection to database server. at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:1.8.0_91] at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) ~[na:1.8.0_91] at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:1.8.0_91] at java.lang.reflect.Constructor.newInstance(Constructor.java:423) ~[na:1.8.0_91] at com.mysql.jdbc.Util.handleNewInstance(Util.java:411) ~[mysql-connector-java-5.1.26.jar:na] at com.mysql.jdbc.Util.getInstance(Util.java:386) ~[mysql-connector-java-5.1.26.jar:na] at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1015) ~[mysql-connector-java-5.1.26.jar:na] at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:989) ~[mysql-connector-java-5.1.26.jar:na] at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:975) ~[mysql-connector-java-5.1.26.jar:na] at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:920) ~[mysql-connector-java-5.1.26.jar:na] at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2568) ~[mysql-connector-java-5.1.26.jar:na] at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2304) ~[mysql-connector-java-5.1.26.jar:na] at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:834) ~[mysql-connector-java-5.1.26.jar:na] at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47) ~[mysql-connector-java-5.1.26.jar:na] at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:1.8.0_91] at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) ~[na:1.8.0_91] at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:1.8.0_91] at java.lang.reflect.Constructor.newInstance(Constructor.java:423) ~[na:1.8.0_91] at com.mysql.jdbc.Util.handleNewInstance(Util.java:411) ~[mysql-connector-java-5.1.26.jar:na] at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:416) ~[mysql-connector-java-5.1.26.jar:na] at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:346) ~[mysql-connector-java-5.1.26.jar:na] at com.zaxxer.hikari.util.DriverDataSource.getConnection(DriverDataSource.java:138) ~[HikariCP-3.4.5.jar:na] at com.zaxxer.hikari.pool.PoolBase.newConnection(PoolBase.java:358) ~[HikariCP-3.4.5.jar:na] at com.zaxxer.hikari.pool.PoolBase.newPoolEntry(PoolBase.java:206) ~[HikariCP-3.4.5.jar:na] at com.zaxxer.hikari.pool.HikariPool.createPoolEntry(HikariPool.java:477) [HikariCP-3.4.5.jar:na] at com.zaxxer.hikari.pool.HikariPool.checkFailFast(HikariPool.java:560) [HikariCP-3.4.5.jar:na] at com.zaxxer.hikari.pool.HikariPool.<init>(HikariPool.java:115) [HikariCP-3.4.5.jar:na] at com.zaxxer.hikari.HikariDataSource.getConnection(HikariDataSource.java:112) [HikariCP-3.4.5.jar:na] at com.baomidou.mybatisplus.extension.spring.MybatisSqlSessionFactoryBean.buildSqlSessionFactory(MybatisSqlSessionFactoryBean.java:591) [mybatis-plus-extension-3.1.0.jar:3.1.0] at com.baomidou.mybatisplus.extension.spring.MybatisSqlSessionFactoryBean.afterPropertiesSet(MybatisSqlSessionFactoryBean.java:422) [mybatis-plus-extension-3.1.0.jar:3.1.0] at com.baomidou.mybatisplus.extension.spring.MybatisSqlSessionFactoryBean.getObject(MybatisSqlSessionFactoryBean.java:636) [mybatis-plus-extension-3.1.0.jar:3.1.0] at com.baomidou.mybatisplus.autoconfigure.MybatisPlusAutoConfiguration.sqlSessionFactory(MybatisPlusAutoConfiguration.java:172) [mybatis-plus-boot-starter-3.1.0.jar:3.1.0] at com.baomidou.mybatisplus.autoconfigure.MybatisPlusAutoConfiguration$$EnhancerBySpringCGLIB$$8bb2ad81.CGLIB$sqlSessionFactory$1(<generated>) [mybatis-plus-boot-starter-3.1.0.jar:3.1.0] at com.baomidou.mybatisplus.autoconfigure.MybatisPlusAutoConfiguration$$EnhancerBySpringCGLIB$$8bb2ad81$$FastClassBySpringCGLIB$$fce7a55a.invoke(<generated>) [mybatis-plus-boot-starter-3.1.0.jar:3.1.0] at org.springframework.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:244) [spring-core-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.context.annotation.ConfigurationClassEnhancer$BeanMethodInterceptor.intercept(ConfigurationClassEnhancer.java:331) [spring-context-5.2.9.RELEASE.jar:5.2.9.RELEASE] at com.baomidou.mybatisplus.autoconfigure.MybatisPlusAutoConfiguration$$EnhancerBySpringCGLIB$$8bb2ad81.sqlSessionFactory(<generated>) [mybatis-plus-boot-starter-3.1.0.jar:3.1.0] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_91] at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_91] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_91] at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_91] at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:154) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.ConstructorResolver.instantiate(ConstructorResolver.java:650) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:635) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1336) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1176) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:556) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:516) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:324) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:322) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:276) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1307) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1227) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireByType(AbstractAutowireCapableBeanFactory.java:1509) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1404) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:593) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:516) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:324) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:322) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) [spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:878) ~[spring-beans-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:879) ~[spring-context-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:551) ~[spring-context-5.2.9.RELEASE.jar:5.2.9.RELEASE] at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:141) ~[spring-boot-2.2.10.RELEASE.jar:2.2.10.RELEASE] at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:747) ~[spring-boot-2.2.10.RELEASE.jar:2.2.10.RELEASE] at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397) ~[spring-boot-2.2.10.RELEASE.jar:2.2.10.RELEASE] at org.springframework.boot.SpringApplication.run(SpringApplication.java:315) ~[spring-boot-2.2.10.RELEASE.jar:2.2.10.RELEASE] at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226) ~[spring-boot-2.2.10.RELEASE.jar:2.2.10.RELEASE] at org.springframework.boot.SpringApplication.run(SpringApplication.java:1215) ~[spring-boot-2.2.10.RELEASE.jar:2.2.10.RELEASE] at com.qsl.PlayItSafeApplication.main(PlayItSafeApplication.java:16) ~[classes/:na] Caused by: java.lang.NullPointerException: null at com.mysql.jdbc.ConnectionImpl.getServerCharacterEncoding(ConnectionImpl.java:3279) ~[mysql-connector-java-5.1.26.jar:na] at com.mysql.jdbc.MysqlIO.sendConnectionAttributes(MysqlIO.java:1940) ~[mysql-connector-java-5.1.26.jar:na] at com.mysql.jdbc.MysqlIO.proceedHandshakeWithPluggableAuthentication(MysqlIO.java:1866) ~[mysql-connector-java-5.1.26.jar:na] at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1252) ~[mysql-connector-java-5.1.26.jar:na] at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2486) ~[mysql-connector-java-5.1.26.jar:na] at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2519) ~[mysql-connector-java-5.1.26.jar:na] ... 62 common frames omitted
關鍵異常堆疊是：
總結
MySQL 驅動版本和 MySQL 版本一定要門當戶對，否則就會錯付
要升就一起升，只升一邊，就會出現升的一方看不上沒升的那方：上岸第一劍 先斬意中人