启动项目时报：Could not create connection to database server.

报错信息：

2019-07-18 15:38:23.309 [Druid-ConnectionPool-Create-562481542] ERROR c.alibaba.druid.pool.DruidDataSource - create connection error, url: jdbc:mysql://localhost:3306/gxs_sms?allowMultiQueries=true&useUnicode=true&characterEncoding=UTF-8&useSSL=false, errorCode 0, state 08001
com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Could not create connection to database server.
	at sun.reflect.GeneratedConstructorAccessor55.newInstance(Unknown Source)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
	at com.mysql.jdbc.Util.handleNewInstance(Util.java:404)
	at com.mysql.jdbc.Util.getInstance(Util.java:387)
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:917)
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:896)
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:885)
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:860)
	at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2332)
	at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2085)
	at com.mysql.jdbc.ConnectionImpl.(ConnectionImpl.java:795)
	at com.mysql.jdbc.JDBC4Connection.(JDBC4Connection.java:44)
	at sun.reflect.GeneratedConstructorAccessor52.newInstance(Unknown Source)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
	at com.mysql.jdbc.Util.handleNewInstance(Util.java:404)
	at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:400)
	at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:327)
	at com.alibaba.druid.filter.FilterChainImpl.connection_connect(FilterChainImpl.java:149)
	at com.alibaba.druid.filter.stat.StatFilter.connection_connect(StatFilter.java:217)
	at com.alibaba.druid.filter.FilterChainImpl.connection_connect(FilterChainImpl.java:143)
	at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1466)
	at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1529)
	at com.alibaba.druid.pool.DruidDataSource$CreateConnectionThread.run(DruidDataSource.java:2185)
Caused by: java.lang.NullPointerException: null
	at com.mysql.jdbc.ConnectionImpl.getServerCharset(ConnectionImpl.java:3005)
	at com.mysql.jdbc.MysqlIO.sendConnectionAttributes(MysqlIO.java:1916)
	at com.mysql.jdbc.MysqlIO.proceedHandshakeWithPluggableAuthentication(MysqlIO.java:1845)
	at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1215)
	at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2255)
	at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2286)
	... 15 common frames omitted

原因：这是因为数据库版本和代码使用的版本不对应导致的。

数据库版本使用的是

代码使用的数据库链接版本是：

5.1.38

所以修改两处的代码：

一、数据库链接驱动

老的：
driverClassName: com.mysql.jdbc.Driver
新的：
driverClassName: com.mysql.cj.jdbc.Driver

二、修改maven的jar包版本

8.0.16