caused by: com.mysql.cj.exceptions.cjcommunicationsexception: communications link failure

这是一个 MySQL 通信链接错误异常，通常是由于与 MySQL 服务器的连接中断导致的。可能的原因包括 MySQL 服务器暂时不可用、连接超时、用户名或密码错误等。建议检查服务器的连接状态以及配置信息，并确保所有必要的端口都已打开。

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Caused by: com.mysql.cj.exceptions.CJCommunicationsException: Communications link failure

这个错误通常是由于无法建立到 MySQL 服务器的连接引起的。这可能是由于以下原因之一：

1. MySQL 服务器已关闭或无法访问。请确保您的 MySQL 服务器正在运行并且可以通过网络连接访问。

2. 您的连接字符串中的主机名或 IP 地址不正确。请确保您的连接字符串正确，主机名或 IP 地址正确。

3. 您的 MySQL 服务器配置不正确。请检查您的 MySQL 服务器配置，并确保它允许远程连接。

4. 您的数据库连接池配置不正确。请检查您的数据库连接池配置，并确保最大连接数等属性正确设置。

您可以尝试使用 MySQL 命令行工具或其他 MySQL 客户端测试您的 MySQL 服务器是否正常运行，并能够通过网络连接访问。如果您能够成功连接到 MySQL 服务器，则可以尝试重新启动您的应用程序或服务器，以解决连接问题。

Caused by: com.mysql.cj.exceptions.CJCommunicationsException: Communications link failure The last

This error message usually indicates a problem with the connection between your application and the MySQL database server. Here are a few things you can try to troubleshoot the issue:

1. Check your network connection: Make sure that your application server can communicate with the MySQL server. Ensure that there are no network issues, such as firewalls or network congestion.

2. Check MySQL server status: Verify that the MySQL server is up and running and that it's listening on the correct port. You can use the command "sudo systemctl status mysql" to check the status of the MySQL server.

3. Check MySQL logs: Check the MySQL error logs for any errors that may be causing the connection failure. The logs are usually located at /var/log/mysql/error.log.

4. Check MySQL configuration: Verify that the MySQL configuration is correct and that the connection parameters in your application code are correct. Check that the database name, username, and password are correct.

5. Increase the connection timeout: If the connection is timing out, increase the connection timeout in your application code or MySQL configuration file.

6. Restart MySQL server: Try restarting the MySQL server to clear any cached connections or other issues that may be causing the problem.

I hope this helps you resolve the issue. Let me know if you have any other questions.