EnityManager Injection via HK2 in WebSockets

问题

I have written 2 WebSocket ServerEndpoints that inject Services that themselves interact with the Database using injected instances of the JPA EntityManager.

The application is a web application deployed on a Tomcat Server, using Jersey as JAX-RS implementation and Hibernate as JPA Provider.

Sometimes it happens that the EntityManager is closed when trying to the DB inside the Endpoints. Also I fear I might have produced code that triggers a Memory Leak.

This is the custom ServerEndpoint.Configurator that I am using (based on https://gist.github.com/facundofarias/7102f5120944c462a5f77a17f295c4d0):

public class Hk2Configurator extends ServerEndpointConfig.Configurator {
    private static ServiceLocator serviceLocator;

    public Hk2Configurator() {
        if (serviceLocator == null) {
            serviceLocator = ServiceLocatorUtilities.createAndPopulateServiceLocator();
            ServiceLocatorUtilities.bind(serviceLocator, new ServicesBinder()); // binds the "normal" Services that interact with the DB

            ServiceLocatorUtilities.bind(serviceLocator, new AbstractBinder() {
                @Override
                protected void configure() {
                    bindFactory(EntityManagerFactory.class).to(EntityManager.class);
                }
            });
        }
    }

    @Override
    public <T> T getEndpointInstance(final Class<T> endpointClass) throws InstantiationException {
        T endpointInstance = super.getEndpointInstance(endpointClass);

        serviceLocator.inject(endpointInstance);

        return endpointInstance;
    }
}

In the rest of the application I am using the same ServicesBinder, but a different Binder for the EntityManager.

The EntityManagerFactory looks like this:

public class EntityManagerFactory implements Factory<EntityManager> {
    private static final javax.persistence.EntityManagerFactory FACTORY = Persistence.createEntityManagerFactory("PersistenceUnit");

    @Override
    public final EntityManager provide() {
        return FACTORY.createEntityManager();
    }

    @Override
    public final void dispose(final EntityManager instance) {
        instance.close();
    }
}

It is loaded with the Scope RequestScoped (only there, not in the WebSocket Endpoints).

I tried creating an EntityManager instance for every access in my DAOs, but then I would run into org.hibernate.LazyInitializationExceptions eventually since my DTOs need an open EntityManager (implicitly).

Any suggestions on how to circumvent the issues I'm having?

回答1:

Okay, I managed to fix my issue by simply rewriting the EntityManager handling to create and close an EntityManager every time I interact with the database.

来源：https://stackoverflow.com/questions/45666129/enitymanager-injection-via-hk2-in-websockets

标签

java

jpa

entitymanager

java-websocket

hk2