Sharing database connection with static methods in Java

Question

I'm working on a java web application using Struts 2. Currently, on each page load, I establish a new db connection, and then close this db connection at the end of the request, just before rendering the resulting HTML. So, each request gets its own db connection.

I want to have a bunch of static methods within my model classes, eg things like User.exists( id ) which would return true if the given user id existed, or false if it didn't. Or other utility methods like User.getEmail(id) or User.disable(id) .

My question is, is there a convenient way to share the db connection with these static methods? Having to pass on the connection as a 2nd argument to all these methods, eg User.exists(id, db) would be ugly, and not too convenient.

What about if I obtain a new db connection in each of these utility methods, and close it before returning the result? Would it have any impact on the perfomance? I could need to call these methods 20-30 times within a request some times (such as when validating user input).

Answer 1

Yes, it is possible. For this case where you want that each Thread has its own Connection, you need to use ThreadLocal , since each request spawn its own Thread. You just need to make sure to close the connection at the end of the request, this is achieved using a Filter .

The filter should be before any other Filter to ensure that the connection is closed at the end of the request.

DBUtil:

public class DBUtil {

    private static ThreadLocal<Connection> connectionHolder = new ThreadLocal<Connection>();

    public static Connection getConnection() {
        Connection connection = connectionHolder.get();
        if (connection == null) {
            //open the connection (lazy loaded)

            //store it
            connectionHolder.set(connection);

        }
        return connectionHolder.get();
    }

    public static void close() {
        Connection connection = connectionHolder.get();
        if (connection != null) {
            //close the connection

            //remove it from the connection holder
            connectionHolder.remove();
        }
    }

}

DBFilter :

public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {       
    try {
        chain.doFilter(request, response);
    } finally {
        DBUtil.close();         
    }
}

It is better if you use a framework for these kind of things, for example Spring Framework already do this by proxying your services and it handles the connection and transaction also gives you a lot of other features.