Tomcat doesn't sync with the mysql database

I'm currently working on a college project, and I'm creating a very simple e-commerce style website.

I'm using JDBC driver manager and connection pool for the connection to the db, while using Tomcat 9.0 as the container.

The problem is: when I modify some product through the website (let's say the amount available for example), the website doesn't always reflect the changes, while I can always see the data correctly in MySql Workbench.

It actually works one time out of two on the same query:

1. I run the query for the first time after the changes -> it shows the old value
2. I run the query for the second time after the changes -> it shows the new value
3. I run the query for the third time after the changes -> it shows the old value

And so on.

I've already tried to set caching off (from the query, using the SQL_NO_CACHE), but it didn't seem to solve the problem, I've tried to use Datasource instead, but it causes other problems that most likely I won't have the time to solve.

This is the connection pool file, which I think might be problem, I'm not that sure tho:

public class DriverManagerConnectionPool  {

private static List<Connection> freeDbConnections;

static {
	freeDbConnections = new LinkedList<Connection>();
	try {
		Class.forName("com.mysql.cj.jdbc.Driver");
	} catch (ClassNotFoundException e) {
		System.out.println("DB driver not found:"+ e.getMessage());
	} 
}

private static synchronized Connection createDBConnection() throws SQLException {
	Connection newConnection = null;
	String ip = "localhost";
	String port = "3306";
	String db = "storage";
	String username = "root";
	String password = "1234";

	newConnection = DriverManager.getConnection("jdbc:mysql://"+ ip+":"+ port+"/"+db+"?useUnicode=true&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC", username, password);

	newConnection.setAutoCommit(false);
	return newConnection;
}


public static synchronized Connection getConnection() throws SQLException {
	Connection connection;

	if (!freeDbConnections.isEmpty()) {
		connection = (Connection) freeDbConnections.get(0);
		freeDbConnections.remove(0);

		try {
			if (connection.isClosed())
				connection = getConnection();
		} catch (SQLException e) {
			connection.close();
			connection = getConnection();
		}
	} else {
		connection = createDBConnection();		
	}

	return connection;
}

public static synchronized void releaseConnection(Connection connection) throws SQLException {
	if(connection != null) freeDbConnections.add(connection);
}

}

I really hope you can help me, I haven't found any solution online!

I guess it is because of auto-commit is disabled. Please try using @Transactional or set auto-commit to true. You can also try to use db.commit after each statement.

As per your connection pool implementation, all connection in your pool seems to be auto committed false. <br>
Please check you have properly committed the connection after executing the query or not. <br>
So it might be the case that, when executing the query after changes with same connection it reflects those changes, done earlier and on other connections, old values are might get returned.