com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet successfully received from the server was XXX milliseconds ago. The last packet sent successfully to the server was XXX milliseconds ago.

[mysqld]
wait_timeout = 28800
interactive_timeout = 28800

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.26</version>
</dependency>

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;

public class MySQLConnectionExample {

    private static final String URL = "jdbc:mysql://localhost:3306/your_database";
    private static final String USER = "your_username";
    private static final String PASSWORD = "your_password";

    private Connection connection;

    public void connect() {
        try {
            // 嘗試建立連接
            connection = DriverManager.getConnection(URL, USER, PASSWORD);
            System.out.println("Connected to the database!");
        } catch (SQLException e) {
            System.err.println("Failed to connect to the database: " + e.getMessage());
            handleCommunicationLinkFailure(e);
        }
    }

    private void handleCommunicationLinkFailure(SQLException e) {
        if (e.getSQLState().equals("08S01")) { // 08S01 是 Communications Link Failure 的 SQLState
            System.err.println("Detected Communications Link Failure. Attempting to reconnect...");
            try {
                Thread.sleep(5000); // 等待 5 秒后重試
                connect(); // 重新嘗試連接
            } catch (InterruptedException ie) {
                Thread.currentThread().interrupt();
                System.err.println("Reconnection attempt interrupted: " + ie.getMessage());
            }
        } else {
            throw new RuntimeException("Unexpected SQL exception", e);
        }
    }

    public void executeQuery(String query) {
        try (Statement statement = connection.createStatement()) {
            statement.executeUpdate(query);
            System.out.println("Query executed successfully: " + query);
        } catch (SQLException e) {
            System.err.println("Failed to execute query: " + e.getMessage());
            handleCommunicationLinkFailure(e);
        }
    }

    public void close() {
        if (connection != null) {
            try {
                connection.close();
                System.out.println("Connection closed.");
            } catch (SQLException e) {
                System.err.println("Failed to close connection: " + e.getMessage());
            }
        }
    }

    public static void main(String[] args) {
        MySQLConnectionExample example = new MySQLConnectionExample();
        example.connect();

        // 執(zhí)行一個(gè)查詢
        example.executeQuery("INSERT INTO your_table (column1, column2) VALUES ('value1', 'value2')");

        // 關(guān)閉連接
        example.close();
    }
}

ping your_mysql_server_ip

sudo systemctl status mysql

sudo systemctl start mysql

sudo ufw status
sudo ufw allow 3306/tcp

[mysqld]
bind-address = 0.0.0.0

sudo systemctl restart mysql

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class MySQLConnectionExample {
    public static void main(String[] args) {
        String url = "jdbc:mysql://your_mysql_server_ip:3306/your_database_name";
        String user = "your_username";
        String password = "your_password";

        try {
            Connection connection = DriverManager.getConnection(url, user, password);
            System.out.println("Connected to the database!");
            // 進(jìn)行數(shù)據(jù)庫操作
            connection.close();
        } catch (SQLException e) {
            e.printStackTrace();
            System.out.println("Failed to connect to the database.");
        }
    }
}

String url = "jdbc:mysql://your_mysql_server_ip:3306/your_database_name?connectTimeout=10000&socketTimeout=10000";

GRANT ALL PRIVILEGES ON your_database_name.* TO 'your_username'@'your_client_ip' IDENTIFIED BY 'your_password';
FLUSH PRIVILEGES;

cat /var/log/mysql/error.log