当 mysql-connector-java-5 遇上 MySQL8，终究还是错付了 → 门当户对真的很重要！

Posted on by hackdl

开心一刻

　　今天，老婆给我发消息

　　老婆：老公，儿子从隔壁邻居家回来了

　　老婆：是先打还是先洗？

　　我：先洗吧，万一打错人了呢

　　老婆：先洗脸吧，没错就边打边洗

起因

　　在我们的固有认知中，mysql-connector-java-5.x.x连接的是MySQL5，而mysql-connector-java-8.x.x连接的是MySQL8

　　如果用mysql-connector-java-5.x.x连接MySQL8，或者用mysql-connector-java-8.x.x连接MySQL5，会出问题

　　至于出什么问题，呃…，我没想过，也没试过，我相信你们也是一样的

　　但无意间，我尝试了下，确实有问题

　　一开始，我的一个demo是基于MySQL 5.7.36、mysql-connector-java 5.1.26、MyBatis-Plus 3.1.0

　　示例代码：play_it_safe

　　因为MySQL 5.7.36被我删了，而本机（windows 10）上正好有MySQL 8.0.26

　　那就用MySQL 8.0.26来跑demo呗，只修改数据库连接的url、username和password

　　然后就出现了一系列的异常

java.math.BigInteger cannot be cast to java.lang.Long

　　启动直接异常

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.(ConnectionImpl.java:834) ~[mysql-connector-java-5.1.26.jar:na]
    at com.mysql.jdbc.JDBC4Connection.(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.(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() [mybatis-plus-boot-starter-3.1.1.jar:3.1.1]
    at com.baomidou.mybatisplus.autoconfigure.MybatisPlusAutoConfiguration$$EnhancerBySpringCGLIB$$8802fc19$$FastClassBySpringCGLIB$$f9d1deeb.invoke() [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() [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.RELEA服务器托管SE]
    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

View Code

　　这确实出乎了我的意料，我认为的是：启动不会异常，运行中出现异常

　　既然异常来了，那就好好看看呗

　　怎么看？直接从异常堆栈中看，找到Caused by

　　直接点击框住的，来到mysql-connector-java 5.1.26的源码

　　这个for循环遍历的是sortedCollationMap，indexEntry则表示遍历的当前元素

　　我问个问题：java.math.BigInteger cannot be cast to java.lang.Long异常是谁抛出来的，getKey()还是intValue()？

　　很简单，用排除法嘛

　　Long是有intValue()方法的，只会NPE，不会java.math.BigInteger cannot be cast to java.lang.Long

　　那就是getKey()抛出的异常呗，我们猜想下什么情况会抛出这个异常

　　indexEntry声明的类型虽然是Map.Entry，但实际它的key不是Long类型，而是BigInteger类型？

　　再往上追溯一下，sortedCollationMap声明的类型是TreeMap，但实际存放元素的key是BigInteger类型？

　　此时你们对这个猜想肯定有疑问：这编译不会报错吗

　　直接put是会编译报错的，但是如果我变通下呢

　　编译没问题，但是执行会有如下异常

　　同样也是int collationIndex = entry.getKey().intValue();抛出的异常

　　但两者原因是否一致，我们还需要对play_it_safe验证

　　如何验证，debug调试呗

　　断点不能打在connectionimpl.java:1019这一行，因为此时是遍历sortedCollationMap，而非往里面put元素

　　我们需要看，往sortedCollationMap里面put的key具体是什么类型，所以断点打在1002行

　　会走 if 分支

　　F7 跟进去

　　key的类型就是BigInteger，证明我们的猜想是对的！

　　但是大家别高兴的太早，根因还没找到，我们得继续跟进com.mysql.jdbc.ResultSetImpl#getObject(int)

　　重点看这个switch

　　继续跟进，你会发现来到BIGINT分支

　　注意，重点来了

　　这段代码很简单，相信大家都能看到，但我还是分 3 块给大家说明下

　　1、unsigned表示无符号，然后再取反则表示有符号，也就是说如果数据库字段类型是有符号的bigint，则用java.lang.Long接收字段值并返回

　　2、如果数据库字段类型是无符号的bigint，则用java.lang.String来接收字段值，如果值为null则直接返回null

　　3、如果数据库字段类型是无符号的bigint，并且字段值不是null，则用java.math.BigInteger来接收字段值并返回

　　此刻相信大家对异常的根因有点明白了，但又没有完全明白，为什么了？

　　因为没有弄清楚来龙去脉，我给大家捋一下：

　　1、程序启动过程（初始化）中，mysql-connector-java 5.1.26 会构建字段级字符集/字符序到java字符编码名称的映射

　　　　也就是会执行com.mysql.jdbc.ConnectionImpl#buildCollationMapping方法

　　2、buildCollationMapping方法中会执行 SQLSHOW COLLATION来获取MySQL的字符集和字符序

　　　　Id：字符序id

　　　　Charset：字符集名称

　　　　关于MySQL的字符集和字符序的更多信息，可查看记一次字符串末尾空白丢失的排查 → MySQL 是会玩的！

　　3、从查询结果集中，逐行取第 3 列（Id ）作为key，取第 2 列（Charset）作为value，put到sortedCollationMap中

　　　　对应代码就是：Util.resultSetToMap(sortedCollationMap, results, 3, 2);

　　4、在取Id列值的时候，会根据数据库列类型，用不同的java类型来接收列值

　　　　MySQL 8.0.26中，COLLATIONS表的ID列的类型是 bigint unsigned

　　　　那么用什么java类型来接收？往上面翻一翻，是不是用java.math.BigInteger来接收？

　　　　MySQL 5.7.36中，COLLATIONS表的ID列的类型却是bigint(11)

　　　　所以用java.lang.Long来接收

　　5、for循环遍历sortedCollationMap，完成数据库字段级字符集/字符序到java字符编码名称的映射

　　　　indexEntry.getKey()在MySQL 8.0.26会抛出异常：java.math.BigInteger cannot be cast to java.lang.Long

　　　　而在MySQL 5.7.36则正常，不抛出异常

　　至此，大家对根因是不是完全明白了？

　　说的简单点就是：mysql-connector-java 5.1.26配不上MySQL 8！

　　说的详细点就是：mysql-connector-java 5.1.26适配的是COLLATIONS的bigint类型的ID，而非bigint unsigned类型的ID

　　说的抽象点就是：上岸第一剑 先斩意中人，MySQL从 5 上岸到了 8，mysql-connector-java如果不跟着上岸的话，会被第一个斩杀

Unknown system variable ‘query_cache_size’

　　因为用的是都说了能不动就别动，非要去调整，出生产事故了吧中的demo：play_it_safe

　　所以我顺手将mysql-connector-java调整到了5.1.37，MySQL还是8.0.26，结果启动出现了另一个异常

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.(ConnectionImpl.java:795) ~[mysql-connector-java-5.1.37.jar:5.1.37]
    at com.mysql.jdbc.JDBC4Connection.(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.(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() [mybatis-plus-boot-starter-3.1.0.jar:3.1.0]
    at com.baomidou.mybatisplus.autoconfigure.MybatisPlusAutoConfiguration$$EnhancerBySpringCGLIB$$eeb10e55$$FastClassBySpringCGLIB$$de0ae008.invoke() [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() [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]

View Code

　　看到这个异常，不知道你们第一反应想到的是什么？

　　我第一反应想到的是MySQL 8取消了查询缓存，而MySQL 5是有查询缓存的

　　异常提示的已经很明显了，我们来验证下

　　MySQL 5.7.36是有系统变量query_cache_size

　　而MySQL 8.0.26是没有的

　　后面我又将mysql-connector-java升级到5.1.42，启动还是异常：Unknown system variable ‘query_cache_size’

Could not create connection to database server

　　因为需要用MySQL 5.7.36做对比，所以还是Docker快速安装了一个MySQL 5.7.36

　　顺带也安装了MySQL 8.0.26（前面用的是Win10版，这个相当于是Linux版本）

　　然后我又鬼使神差的将连接调整到了Linux版的MySQL 8.0.26

　　当mysql-connector-java是5.1.42时，启动异常是：Unknown system variable ‘query_cache_size’

　　当mysql-connector-java是5.1.37时，启动异常是：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.(ConnectionImpl.java:795) ~[mysql-connector-java-5.1.37.jar:5.1.37]
    at com.mysql.jdbc.JDBC4Connection.(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.(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() [mybatis-plus-boot-starter-3.1.0.jar:3.1.0]
    at com.baomidou.mybatisplus.autoconfigure.MybatisPlusAutoConfiguration$$EnhancerBySpringCGLIB$$b0a04890$$FastClassBySpringCGLIB$$b0fb4ddc.invoke() [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() [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

View Code

　　关键异常堆栈是：

　　真正的异常其实是NPE，大家可以参考前面讲到的方法去分析

　　当mysql-connector-java是5.1.26时，启动异常也是：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.(ConnectionImpl.java:834) ~[mysql-connector-java-5.1.26.jar:na]
    at com.mysql.jdbc.JDBC4Connection.(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.(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() [mybatis-plus-boot-starter-3.1.0.jar:3.1.0]
    at com.baomidou.mybatisplus.autoconfigure.MybatisPlusAutoConfiguration$$EnhancerBySpringCGLIB$$8bb2ad81$$FastClassBySpringCGLIB$$fce7a55a.invoke() [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() [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(ServletWebSer服务器托管verApplicationContext.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

View Code

　　关键异常堆栈是：

总结

　　MySQL驱动版本和MySQL版本一定要门当户对，否则就会错付

　　要升就一起升，只升一边，就会出现升的一方看不上没升的那方：上岸第一剑 先斩意中人

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