public interface PerfStatistics {
    String getOpenJPAStatistics();
    String getEntityClasses();
}

@Stateless
public class PerfStatisticsImpl implements PerfStatistics {
    @Inject
    private EntityManagerJPAFactory entityManagerFactory;
    private OpenJPAEntityManagerFactory openJPAEntityManagerFactory;

    @PostConstruct
    public void init() {
        openJPAEntityManagerFactory = OpenJPAPersistence.cast(entityManagerFactory.getEntityManager().getEntityManagerFactory());
    }

    @Override
    public String getOpenJPAStatistics() {
        StoreCache cache = openJPAEntityManagerFactory.getStoreCache();

        CacheStatistics st = cache.getStatistics();
        return String.format("{ \"ReadCount\": %d, \"HitCount\": %d, \"WriteCount\": %d }", st.getReadCount(), st.getHitCount(), st.getWriteCount());
    }

    @Override
    public String getEntityClasses() {
        StringBuilder res = new StringBuilder("{ \"Entities\": [");

        EntityManagerFactory emf = openJPAEntityManagerFactory;
        EntityManager em = emf.createEntityManager();
        Cache cache = emf.getCache();
        for(EntityType<?> entityType : em.getMetamodel().getEntities()) {
            Class<?> cls = entityType.getBindableJavaType();
            res.append(String.format("\"%s\", ", cls.getCanonicalName()));
        }
        res.append("\"\"], \"Cache\": \"");
        res.append(cache.toString());
        res.append("\" }");
        return res.toString();
    }
}