一、异常信息

com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Could not create connection to database server.
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:1.8.0_231]
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) ~[na:1.8.0_231]
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:1.8.0_231]
    at java.lang.reflect.Constructor.newInstance(Constructor.java:423) ~[na:1.8.0_231]
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:389) ~[mysql-connector-java-5.1.35.jar:5.1.35]
    at com.mysql.jdbc.Util.getInstance(Util.java:372) ~[mysql-connector-java-5.1.35.jar:5.1.35]
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:958) ~[mysql-connector-java-5.1.35.jar:5.1.35]
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:937) ~[mysql-connector-java-5.1.35.jar:5.1.35]
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:926) ~[mysql-connector-java-5.1.35.jar:5.1.35]
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:872) ~[mysql-connector-java-5.1.35.
Caused by: java.lang.NullPointerException: null
    at com.mysql.jdbc.ConnectionImpl.getServerCharset(ConnectionImpl.java:2989) ~[mysql-connector-java-5.1.35.jar:5.1.35]
    at com.mysql.jdbc.MysqlIO.sendConnectionAttributes(MysqlIO.java:1873) ~[mysql-connector-java-5.1.35.jar:5.1.35]
    at com.mysql.jdbc.MysqlIO.proceedHandshakeWithPluggableAuthentication(MysqlIO.java:1802) ~[mysql-connector-java-5.1.35.jar:5.1.35]
    at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1206) ~[mysql-connector-java-5.1.35.jar:5.1.35]
    at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2239) ~[mysql-connector-java-5.1.35.jar:5.1.35]
    at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2270) ~[mysql-connector-java-5.1.35.jar:5.1.35]
    ... 105 common frames omitted

二、解决办法

1、查看你的mysql版本

select version();

比如我的版本是：8.0.3

2、更新mysql-connector-java的版本与mysql的版本一致是8版本

<!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.20</version>
</dependency>