Is there a way to re-use the MySQL Db connection in Java App Engine

Question

I want to re-use a java.sql.Connection object. It is with Google App Engine so connection pooling is not an option (I think?). Normally I just create a new connection per servlet call, but now I have functions being called from the servlet and I don't want to create a new connection on each function call (unless I know it will be very fast), e.g.

    public void someServlet() { // Called from web page - speed is thus of concern
        try (Connection con = DriverManager.getConnection("connection string")) { // might be slow - want to re-use con
            // Do something with connection, e.g. run some queries
            someSQLFunction();
            someSQLFunction();
            someSQLFunction();
        } catch (SQLException e) {
            // Some error handling
        }
    }

    public void someSQLFunction() throws SQLException {
        // I don't want to re-create another Connection here, but use the one from the servlet.
        try (Connection con = DriverManager.getConnection("connection string")) { // might be slow - want to re-use con
            // Do something with connection, e.g. run some queries
            return;
        }
    }

How can I re-use the Connection object of the servlet within someSQLFunction()?

Mario · Accepted Answer · 2014-09-01 14:05:43Z

1

In App Engine, the front end is thought to serve web requests, and part of the design is its ability to be moved among instances, deleted or started as needed. That means that your connection object could be invalid when used from another method in your Servlet.

As an alternative you could use Datastore where you don't need to set up connections or Google Cloud SQL

On the other hand, if you need it so much to use your own MySQL, you could keep the connection alive in a module [1] that may outlive front-end requests. As an example you could add tasks to a pull queue, and the module would consume the nexts tasks from it, while keeping the connection.

In this case, the response speed wouldn't be as fast as using Datastore.

[1] App Engine Modules - https://developers.google.com/appengine/docs/java/modules/

answered Sep 1, 2014 at 14:05

Mario

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2 Comments

Floris Over a year ago

Thanks for your reply. I only need to re-use the connection during a single request though as shown in my code snippet.

Mario Over a year ago

Why don't you assign it to a local class variable that is accessible from any method?

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