导致的异常

2021-07-14 14:45:13.294 ERROR 16356 --- [eate-2061818462] com.alibaba.druid.pool.DruidDataSource   : create connection error, url: jdbc:mysql://127.0.0.1:3306/college?characterEncoding=utf-8, errorCode 0, state 08001

com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Could not create connection to database server.
	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:1.8.0_291]
	at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) ~[na:1.8.0_291]
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:1.8.0_291]
	at java.lang.reflect.Constructor.newInstance(Constructor.java:423) ~[na:1.8.0_291]
	at com.mysql.jdbc.Util.handleNewInstance(Util.java:411) ~[mysql-connector-java-5.1.25.jar:na]
	at com.mysql.jdbc.Util.getInstance(Util.java:386) ~[mysql-connector-java-5.1.25.jar:na]
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1015) ~[mysql-connector-java-5.1.25.jar:na]
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:989) ~[mysql-connector-java-5.1.25.jar:na]
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:975) ~[mysql-connector-java-5.1.25.jar:na]
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:920) ~[mysql-connector-java-5.1.25.jar:na]
	at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2565) ~[mysql-connector-java-5.1.25.jar:na]
	at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2301) ~[mysql-connector-java-5.1.25.jar:na]
	at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:834) ~[mysql-connector-java-5.1.25.jar:na]
	at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47) ~[mysql-connector-java-5.1.25.jar:na]
	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:1.8.0_291]
	at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) ~[na:1.8.0_291]
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:1.8.0_291]
	at java.lang.reflect.Constructor.newInstance(Constructor.java:423) ~[na:1.8.0_291]
	at com.mysql.jdbc.Util.handleNewInstance(Util.java:411) ~[mysql-connector-java-5.1.25.jar:na]
	at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:416) ~[mysql-connector-java-5.1.25.jar:na]
	at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:346) ~[mysql-connector-java-5.1.25.jar:na]
	at com.alibaba.druid.filter.FilterChainImpl.connection_connect(FilterChainImpl.java:148) ~[druid-1.1.0.jar:1.1.0]
	at com.alibaba.druid.filter.stat.StatFilter.connection_connect(StatFilter.java:217) ~[druid-1.1.0.jar:1.1.0]
	at com.alibaba.druid.filter.FilterChainImpl.connection_connect(FilterChainImpl.java:142) ~[druid-1.1.0.jar:1.1.0]
	at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1466) ~[druid-1.1.0.jar:1.1.0]
	at com.alibaba.druid.pool.DruidAbstractDataSource.createPhysicalConnection(DruidAbstractDataSource.java:1529) ~[druid-1.1.0.jar:1.1.0]
	at com.alibaba.druid.pool.DruidDataSource$CreateConnectionThread.run(DruidDataSource.java:2178) ~[druid-1.1.0.jar:1.1.0]
Caused by: java.lang.NullPointerException: null
	at com.mysql.jdbc.ConnectionImpl.getServerCharacterEncoding(ConnectionImpl.java:3276) ~[mysql-connector-java-5.1.25.jar:na]
	at com.mysql.jdbc.MysqlIO.sendConnectionAttributes(MysqlIO.java:1940) ~[mysql-connector-java-5.1.25.jar:na]
	at com.mysql.jdbc.MysqlIO.proceedHandshakeWithPluggableAuthentication(MysqlIO.java:1866) ~[mysql-connector-java-5.1.25.jar:na]
	at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1252) ~[mysql-connector-java-5.1.25.jar:na]
	at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2483) ~[mysql-connector-java-5.1.25.jar:na]
	at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2516) ~[mysql-connector-java-5.1.25.jar:na]
	... 16 common frames omitted

遇到这种情况的一般是MySQL版本冲突，检查pom中数据库的版本

pom.xml

<dependency>
	<groupId>mysql</groupId>
	<artifactId>mysql-connector-java</artifactId>
	<version>5.1.25</version>
</dependency>

我导入的是5.1.25版本 但是我的是MySQL8版本，所以出现了错误，改成和版本对应的即可

解决方式

1.查看数据库版本

--查看数据库版本
select version(); 
-- 我查询的结果 8.0.25

2.根据版本修改pom文件

<!-- 改成和数据库对应的版本即可 -->
<dependency>
	<groupId>mysql</groupId>
	<artifactId>mysql-connector-java</artifactId>
	<version>8.0.25</version>
</dependency>