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.<init>(ConnectionImpl.java:795) at com.mysql.jdbc.JDBC4Connection.<init>(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：

<mysql.version>5.1.38</mysql.version>

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

<mysql.version>8.0.16</mysql.version>