com.mysql.cj.jdbc.exceptions.CommunicationsException：从服务器成功收到的最后一个数据包是XXXXXXXXXXXX毫秒前

Question

I have a spring boot application that does not use connection pool and we didn't want to open a DB connection at every request

So, here is what we have in a class called MySQLService which has methods with DB queries:

    @Autowired
    @Qualifier("mysqlDB")
    private Connection connection;

This connection object is always used in all of the methods with queries.

In MySQLConnection class,

 @Bean(name = "mysqlDB")
    public Connection getConnection() {
        Connection connection = null;
        try {
            Class.forName(mysqlDriver);
            LOGGER.debug("get mysql connection...");
            connection = DriverManager
                    .getConnection(jdbcUrl,
                            user, password);
        } catch (Exception exception) {
            LOGGER.error("ERROR :: {}", exception);
                        }    
        return connection;
    }
}

So, we are never really closing the connection, it is being managed by spring context but since we are not using JDBCTemplates, it does not get closed. We have autoreconnect set to true in connection string.

In a day or two, we get the exception:

com.mysql.cj.jdbc.exceptions.CommunicationsException: The last packet successfully received from the server was 61,183,452 milliseconds ago.

I understand it is because SQL Server has connection lifetime set so it expires the connection but what is a way to handle this without using a connection pool

Answer 1

Schedule a ping to the MySQL Server every 6 hours or so, executing this query: select 1 from dual . For that, you need to enable scheduling:

@Configuration
@EnableScheduling
public class SpringConfig {
    //...
}

then:

@Scheduled(cron = "0 */6 * * *")
public void schedulePingMySQL() {
   // execute `select 1 from dual`
}

Anyway, using a connection pool is the recommended way. This case the code may look like:

 @Autowired
private DataSource dataSource;

public void save (Dto dto) {
    Connection con = dataSource.getConnection();
    // finally, close the connection
}