Java的报错解决： Cause: com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure

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本文介绍了在学习MyBatis时遇到的CommunicationsLinkFailure问题，该问题导致数据库更新失败。作者提供了详细的错误日志，并指出问题可能与SSL连接有关。通过在jdbc.properties的URL中添加`useSSL=false`参数，成功解决了该问题，确保了与MySQL8服务器的连接。此解决方案适用于遇到相同警告信息的开发者。

我们在学习mybatis中会出现Communications link failure报错，我当时找了一天都没有找到合适的解决方案

Sun Aug 07 08:30:43 CST 2022 WARN: Establishing SSL connection without server's identity verification is not recommended. 
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.
 
org.apache.ibatis.exceptions.PersistenceException: 
 Error updating database.  Cause: com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure
 
The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
 The error may exist in mappers/userMapper.xml
The error may involve com.example.mapper.userMapper.insertUser
The error occurred while executing an update
Cause: com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure

下面是我的jdbc.properties中的内容

driver=com.mysql.cj.jdbc.Driver
url=jdbc:mysql://localhost:3306/ssm?serverTimezone=UTC
username=root
password=123456

解决方法：在url中添加useSSL=false,就可以解决，不知道你们的是否和我的一样，我的mysql是8版本的。

driver=com.mysql.cj.jdbc.Driver
url=jdbc:mysql://localhost:3306/ssm?useSSL=false&serverTimezone=UTC
username=root
password=123456

我感觉可能是下面这个代码的报错引起Communications link failure，在url中添加useSSL=false就是解决下面的报错的，如果你没有下面的报错，可能这个方法就不好使了

Sun Aug 07 08:30:43 CST 2022 WARN: Establishing SSL connection without server's identity verification is not recommended. 
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.