/**
   * Gets Hibernate session.
   *
   * @param tx Cache transaction.
   * @return Session.
   */
  Session session(@Nullable GridCacheTx tx) {
    Session ses;

    if (tx != null) {
      ses = tx.meta(ATTR_SES);

      if (ses == null) {
        ses = sesFactory.openSession();

        ses.beginTransaction();

        // Store session in transaction metadata, so it can be accessed
        // for other operations on the same transaction.
        tx.addMeta(ATTR_SES, ses);

        if (log.isDebugEnabled())
          log.debug("Hibernate session open [ses=" + ses + ", tx=" + tx.xid() + "]");
      }
    } else {
      ses = sesFactory.openSession();

      ses.beginTransaction();
    }

    return ses;
  }
  /** {@inheritDoc} */
  @Override
  public void txEnd(GridCacheTx tx, boolean commit) throws GridException {
    init();

    Session ses = tx.removeMeta(ATTR_SES);

    if (ses != null) {
      Transaction hTx = ses.getTransaction();

      if (hTx != null) {
        try {
          if (commit) {
            ses.flush();

            hTx.commit();
          } else hTx.rollback();

          if (log.isDebugEnabled())
            log.debug("Transaction ended [xid=" + tx.xid() + ", commit=" + commit + ']');
        } catch (HibernateException e) {
          throw new GridException(
              "Failed to end transaction [xid=" + tx.xid() + ", commit=" + commit + ']', e);
        } finally {
          ses.close();
        }
      }
    }
  }
  /** {@inheritDoc} */
  @Override
  public void put(@Nullable GridCacheTx tx, K key, @Nullable V val) throws GridException {
    init();

    if (log.isDebugEnabled())
      log.debug("Store put [key=" + key + ", val=" + val + ", tx=" + tx + ']');

    if (val == null) {
      remove(tx, key);

      return;
    }

    Session ses = session(tx);

    try {
      GridCacheHibernateBlobStoreEntry entry =
          new GridCacheHibernateBlobStoreEntry(toBytes(key), toBytes(val));

      ses.saveOrUpdate(entry);
    } catch (HibernateException e) {
      rollback(ses, tx);

      throw new GridException(
          "Failed to put value to cache store [key=" + key + ", val" + val + "]", e);
    } finally {
      end(ses, tx);
    }
  }
  /** {@inheritDoc} */
  @SuppressWarnings({"unchecked", "RedundantTypeArguments"})
  @Override
  public V load(@Nullable GridCacheTx tx, K key) throws GridException {
    init();

    if (log.isDebugEnabled()) log.debug("Store load [key=" + key + ", tx=" + tx + ']');

    Session ses = session(tx);

    try {
      GridCacheHibernateBlobStoreEntry entry =
          (GridCacheHibernateBlobStoreEntry)
              ses.get(GridCacheHibernateBlobStoreEntry.class, toBytes(key));

      if (entry == null) return null;

      return fromBytes(entry.getValue());
    } catch (HibernateException e) {
      rollback(ses, tx);

      throw new GridException("Failed to load value from cache store with key: " + key, e);
    } finally {
      end(ses, tx);
    }
  }
  /** {@inheritDoc} */
  @SuppressWarnings({"JpaQueryApiInspection", "JpaQlInspection"})
  @Override
  public void remove(@Nullable GridCacheTx tx, K key) throws GridException {
    init();

    if (log.isDebugEnabled()) log.debug("Store remove [key=" + key + ", tx=" + tx + ']');

    Session ses = session(tx);

    try {
      Object obj = ses.get(GridCacheHibernateBlobStoreEntry.class, toBytes(key));

      if (obj != null) ses.delete(obj);
    } catch (HibernateException e) {
      rollback(ses, tx);

      throw new GridException("Failed to remove value from cache store with key: " + key, e);
    } finally {
      end(ses, tx);
    }
  }
  /**
   * Checks availability of a classpath resource.
   *
   * @param name Resource name.
   * @return {@code true} if resource is available and ready for read, {@code false} otherwise.
   */
  private boolean resourceAvailable(String name) {
    InputStream cfgStream =
        Thread.currentThread().getContextClassLoader().getResourceAsStream(name);

    if (cfgStream == null) {
      log.error("Classpath resource not found: " + name);

      return false;
    }

    try {
      // Read a single byte to force actual content access by JVM.
      cfgStream.read();

      return true;
    } catch (IOException e) {
      log.error("Failed to read classpath resource: " + name, e);

      return false;
    } finally {
      U.close(cfgStream, log);
    }
  }
  /**
   * Initializes store.
   *
   * @throws GridException If failed to initialize.
   */
  private void init() throws GridException {
    if (initGuard.compareAndSet(false, true)) {
      if (log.isDebugEnabled()) log.debug("Initializing cache store.");

      try {
        if (sesFactory != null)
          // Session factory has been provided - nothing to do.
          return;

        if (!F.isEmpty(hibernateCfgPath)) {
          try {
            URL url = new URL(hibernateCfgPath);

            sesFactory = new Configuration().configure(url).buildSessionFactory();

            if (log.isDebugEnabled()) log.debug("Configured session factory using URL: " + url);

            // Session factory has been successfully initialized.
            return;
          } catch (MalformedURLException e) {
            if (log.isDebugEnabled())
              log.debug("Caught malformed URL exception: " + e.getMessage());
          }

          // Provided path is not a valid URL. File?
          File cfgFile = new File(hibernateCfgPath);

          if (cfgFile.exists()) {
            sesFactory = new Configuration().configure(cfgFile).buildSessionFactory();

            if (log.isDebugEnabled())
              log.debug("Configured session factory using file: " + hibernateCfgPath);

            // Session factory has been successfully initialized.
            return;
          }

          // Provided path is not a file. Classpath resource?
          sesFactory = new Configuration().configure(hibernateCfgPath).buildSessionFactory();

          if (log.isDebugEnabled())
            log.debug("Configured session factory using classpath resource: " + hibernateCfgPath);
        } else {
          if (hibernateProps == null) {
            U.warn(
                log, "No Hibernate configuration has been provided for store (will use default).");

            hibernateProps = new Properties();

            hibernateProps.setProperty("hibernate.connection.url", DFLT_CONN_URL);
            hibernateProps.setProperty("hibernate.show_sql", DFLT_SHOW_SQL);
            hibernateProps.setProperty("hibernate.hbm2ddl.auto", DFLT_HBM2DDL_AUTO);
          }

          Configuration cfg = new Configuration();

          cfg.setProperties(hibernateProps);

          assert resourceAvailable(MAPPING_RESOURCE);

          cfg.addResource(MAPPING_RESOURCE);

          sesFactory = cfg.buildSessionFactory();

          if (log.isDebugEnabled())
            log.debug("Configured session factory using properties: " + hibernateProps);
        }
      } catch (HibernateException e) {
        throw new GridException("Failed to initialize store.", e);
      } finally {
        initLatch.countDown();
      }
    } else if (initLatch.getCount() > 0) U.await(initLatch);

    if (sesFactory == null) throw new GridException("Cache store was not properly initialized.");
  }