Question

I am using Guice with JDO and Datanucleus in my desktop app. I am facing a NPE that I can’t fix, so I hope someone can help me 🙂

I am using properly configured H2 db, with schema created and all my classes are nicely enhanced, so it’s not that. Anyway, I am getting NPE here, at JDORepository class:

public abstract class JdoRepository<T> implements Repository<T>
{
private final Class<T> clazz;
private final Provider<PersistenceManager> pmProvider;

protected JdoRepository(Class<T> clazz, Provider<PersistenceManager> pmProvider)
{
    this.clazz = clazz;
    this.pmProvider = pmProvider;
}
public void persist(T entity)
{
    pmProvider.get().makePersistent(entity);   <---- NPE!
}

My PersistenceManagerFilter looks like that:

    @Singleton
    public class PersistenceManagerFilter implements Filter
    {
    private static final Logger logger =  Logger.getLogger(PersistenceManagerFilter.class.getName());

    private static final ThreadLocal<PersistenceManager> pm = new  ThreadLocal<PersistenceManager>();

    private PersistenceManagerFactory pmf;

    public void init(FilterConfig filterConfig) throws ServletException
    {
        logger.info("Creating PersistenceManagerFactory");
        pmf = JDOHelper.getPersistenceManagerFactory();
    }

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain  chain)
            throws IOException, ServletException
    {
        try
        {
            pm.set(pmf.getPersistenceManager());
            chain.doFilter(request, response);
        }
        finally
        {
            pm.get().close();
        }
    }

    public void destroy()
    {
        logger.info("Closing PersistenceManagerFactory");
        pmf.close();
    }

    /**
     * This module binds the JDO {@link javax.jdo.PersistenceManager} interface to the  provider that allows the
     * implementation to be injected as Provider&lt;PersistenceManager&gt;.
     */
    public static class GuiceModule extends AbstractModule
    {
        @Override
        protected void configure()
        {
            bind(PersistenceManager.class).toProvider(new Provider<PersistenceManager>()
            {
                public PersistenceManager get()
                {
                    return PersistenceManagerFilter.pm.get();
                }
            });
        }
    }
}

And the responsible module:

    public class GuiceModule extends AbstractModule
   {
   @Override
   protected void configure()
   {
       // Enable per-request-thread PersistenceManager injection.
       install(new PersistenceManagerFilter.GuiceModule());
       bind(new TypeLiteral<Repository<Project>>() { }).to(JdoProjectRepository.class);

I am initiating it all that way:

Injector injector = Guice.createInjector(new GuiceModule());
    Main main = injector.getInstance(Main.class);
    main.run();

So repository bindings in main class work fine, as they are redirected to JDORepository. It’s something at lower level, PMF not getting bound properly? Any ideas?

Answer 1

What does your main.run()-method do? Does it call PersistenceManagerFilter#doFilter? If it doesn’t, the value in yourThreadLocal<PersistenceManager> will be null…

You could override the initialValue() and do something like this:

ThreadLocal<PersistenceManager> pm = new  ThreadLocal<PersistenceManager>(){
    @Override
    protected PersistenceManager initialValue() {
        return JDOHelper.getPersistenceManagerFactory().getPersistenceManager();
    }
};

You should also remember to call the ThreadLocal#remove() method in your finally-block.

Instead of handling the ThreadLocal yourself, you could bind the PersistenceManager directly in the guice-module:

class GuiceModule extends AbstractModule {

    @Provides @RequestScoped
    PersistenceManager providePersistenceManager(){
        return JDOHelper.getPersistenceManagerFactory().getPersistenceManager();
    }

    @Override
    protected void configure() {}
}