About troubleshooting MySQL driver version errors, cause: com mysql. jdbc. exceptions. jdbc4、Unknown system variable ‘query_ cache_ size

Error01 in the light of Maven Project dependence mysql Driver version mismatch

querying database. Cause: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Could not create connection to database server. Attempted reconnect 3 times. Giving up.

ERR02 mysql Driver version mismatch

java.sql.Exception in thread “main” java.sql.SQLException: Unknown system variable ‘query_cache_size’

mysql-connecter-java The version of is too low , The database driver does not correspond to the database version

` error 1：
java.sql.Exception in thread "main" java.sql.SQLException: Unknown system variable 'query_cache_size'
` error 2：
java.sql.SQLException: Unknown system variable 'language'

` reason 
mysql-connecter-java The version of is too low , The database driver does not correspond to the database version 

` solve 
1、 Replace the tool kit 
mysql-connecter-java-5.1.47.jar  Can match  mysql8.0+

2、 modify  pom file 
 Such as mybatis Use  mysql-5.1.14 Driver program , and mybatis The configured data source is connected to  mysql-8.0.11 ,
 modify  pom file , as follows ：
<dependency>    
    <groupId>mysql</groupId>    
    <artifactId>mysql-connector-java</artifactId>   
    <version>8.0.11</version>  #  Change to 8.0+ The version will do .
</dependency>

 Officially ：
The query cache is deprecated as of MySQL 5.7.20, and is removed in MySQL 8.0. Deprecation includes query_cache_size.
 Meaning : Is the query cached in MySQL 5.7.20 Has abandoned , stay MySQL 8.0 Has been removed from . Abandonment includes query_cache_size.

Error03：jdbc Of Aim at mysql8+ Version of URL SSL Verification questions

WARN:hu Apr 15 12:27:34 CST 2021 WARN: Establishing SSL connection Establishing SSL connection without server’s identity verificati

hu Apr 15 12:27:34 CST 2021 WARN: Establishing SSL connection Establishing SSL connection without server's identity verificatio
According to MySQL 5.5.45+, 5.6.26+ and 5.7.6+ requirements SSL connection must be established by default if explicit option isn't set. For compliance with existing applications not using SSL the verifyServerCertificate property is set to 'false'. You need either to explicitly disable SSL by setting useSSL=false, or set useSSL=true and provide truststore for server certificate verification.

#  solve ： 
#  stay jdbcURL Adding such a line of code to the attribute tag will skip SSL verification 
?serverTimezone=GMT%2B8&useUnicode=true&characterEncoding=utf8&autoReconnect=true&useSSL=false
 for example ：
Connection connect = DriverManager.getConnection( 
"jdbc:mysql://localhost:3306/ Database name ?serverTimezone=GMT%2B8&useUnicode=true&characterEncoding=utf8&autoReconnect=true&useSSL=false","root","root");

EER04：junit-4.11 The above version does not include hamcrest.

java.lang.NoClassDefFoundError: org/hamcrest/SelfDescribing

junit  Unit test error java.lang.NoClassDefFoundError: org/hamcrest/SelfDescribing

Caused by: java.lang.ClassNotFoundException: org.hamcrest.SelfDescribing
    at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:583)
    at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:178)
    at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:521)
    ... 19 more

 reason 

junit-4.11 The above version does not include hamcrest.
 resolvent 

 Method 1 ：junit Version down to 4.11 following 

 Method 2 ： Join in hamcrest-core-1.3.jar package 

Err05 ： The path in the property set configuration file cannot have spaces , Otherwise, the report will be wrong ： org.apache.ibatis.exceptions.PersistenceException ,Error building SqlSession.

org.apache.ibatis.exceptions.PersistenceException: 
### Error building SqlSession.
### The error may exist in configstatic/UserMapper.xml
### Cause: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: org.apache.ibatis.builder.BuilderException: Error parsing Mapper XML. The XML location is 'configstatic/UserMapper.xml'. Cause: org.apache.ibatis.builder.BuilderException: Error resolving class. Cause: org.apache.ibatis.type.TypeException: Could not resolve type alias ' com.itheima.mb.pojo.User'.  Cause: java.lang.ClassNotFoundException: Cannot find class:  com.itheima.mb.pojo.User

 The file path cannot have spaces