Question

EDIT:
The current code is the working solution, the one which does not block the application, it
incorporates the suggestion made in the approved answer.

---

I want a background thread to download an MS Access database continuously, while my tomcat 7 web application is running, the thread does download the database, however it seems to block my application’s startup as I’m unable to access any page from the service, this is the code that I’m using:

public class DatabaseUpdater implements ServletContextListener {
    private Thread thread = null;

    private final Runnable updater = new Runnable() {

        private boolean hasExpired(File mdbFile) throws IOException {
            if (!mdbFile.exists())
                return true;

            Long ttl = Long.parseLong(Configuration.getValueForOS("db.http-expiration"));

            Date now = new Date();
            Date fileDate = new Date(mdbFile.lastModified());

            return (now.getTime() - fileDate.getTime()) > ttl;
        }

        @Override
        public void run() {
            while (true) {
                if (Thread.currentThread().isInterrupted())
                    throw new RuntimeException("Application Shutdown");

                try {
                    String databases[] = new String[]{"database1", "database2"};
                    for (String database : databases) {

                        String fileName = database + "." + StringUtil.randomString(8) + ".mdb";
                        String fileLocation = Configuration.getValueForOS("db.path");

                        File mdbFile = new File(fileLocation, fileName);
                        File currentDatabaseFile = new File(fileLocation, database + ".mdb");

                        if (hasExpired(currentDatabaseFile)) {
                            URL url = new URL(Configuration.getValueForOS("db.url." + database));
                            InputStream in = url.openConnection().getInputStream();
                            OutputStream out = new FileOutputStream(mdbFile);

                            FileUtil.streamBridge(in, out);
                            FileUtil.close(in, out);

                            while (currentDatabaseFile.exists() && !currentDatabaseFile.delete()) ;
                            while (!mdbFile.renameTo(currentDatabaseFile)) ;
                       }
                   }
                     // Put the thread to sleep so the other threads do not starve
                    Thread.sleep(Long.parseLong(
                        Configuration.getValueForOS("db.http-expiration"));
                } catch (IOException ioe) {
                    ioe.printStackTrace();
                } catch (InterruptedException ie) {
                    ie.printStackTrace();
                }
            }
        }
    };

    @Override
    public void contextInitialized(ServletContextEvent servletContextEvent) {
        this.thread = new Thread(updater);
        thread.start();
    }

    @Override
    public void contextDestroyed(ServletContextEvent servletContextEvent) {
        if (this.thread.isAlive())
            this.thread.interrupt();
    }
}

What could be causing?

I based my implementation on this question: Background Thread for a Tomcat servlet app

Answer 1

Given that your code loops forever, you’re probably starving all the other threads in the VM. Try sleeping the thread once in a while.