To prevent a memory leak, the JDBC Driver has been forcibly unregistered

Question

I am getting this message when I run my web application. It runs fine but I get this message during shutdown.

SEVERE: A web application registered the

Answer 1

I see this issue come up a lot. Yes, Tomcat 7 does automatically deregister it, but it that REALLY taking control of your code and a good coding practice? Surely YOU want to know that you have all the correct code in place to close all your objects, shut down database connection pool threads, and get rid of all warnings. I certainly do.

This is how I do it.

Step 1: Register a Listener

web.xml

    com.mysite.MySpecialListener

Step 2: Implement the Listener

com.mysite.MySpecialListener.java

public class MySpecialListener implements ServletContextListener {

    @Override
    public void contextInitialized(ServletContextEvent sce) {
        // On Application Startup, please…

        // Usually I'll make a singleton in here, set up my pool, etc.
    }

    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        // On Application Shutdown, please…

        // 1. Go fetch that DataSource
        Context initContext = new InitialContext();
        Context envContext  = (Context)initContext.lookup("java:/comp/env");
        DataSource datasource = (DataSource)envContext.lookup("jdbc/database");

        // 2. Deregister Driver
        try {
            java.sql.Driver mySqlDriver = DriverManager.getDriver("jdbc:mysql://localhost:3306/");
            DriverManager.deregisterDriver(mySqlDriver);
        } catch (SQLException ex) {
            logger.info("Could not deregister driver:".concat(ex.getMessage()));
        } 

        // 3. For added safety, remove the reference to dataSource for GC to enjoy.
        dataSource = null;
    }

}

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