queuedestinationcache.java

来自「OpenJMS是一个开源的Java Message Service API 1.」· Java 代码 · 共 523 行 · 第 1/2 页

            MessageHandle handle = handles[i];
            MessageImpl message = handle.getMessage();
            if (message != null) {
                browser.messageAdded(handle, message);
            }
        }
    }

    /**
     * Return a message handle back to the cache, to recover unsent or
     * unacknowledged messages.
     *
     * @param handle the message handle to return
     */
    public void returnMessageHandle(MessageHandle handle) {
        // add the message to the destination cache
        _handles.add(handle);
        try {
            MessageImpl message = handle.getMessage();
            if (message != null) {
                // if there are any registered consumers, notify one of them
                // that a message has arrived
                ConsumerEndpoint consumer = getConsumerForMessage(message);
                if (consumer != null) {
                    consumer.messageAdded(handle, message);
                }
            }
        } catch (JMSException exception) {
            _log.debug(exception, exception);
        }
    }

    /**
     * Determines if there are any registered consumers.
     *
     * @return <code>true</code> if there are registered consumers
     */
    public boolean hasConsumers() {
        boolean active = super.hasConsumers();
        if (!active && !_browsers.isEmpty()) {
            active = true;
        }
        if (_log.isDebugEnabled()) {
            _log.debug("hasActiveConsumers()[queue=" + getDestination() + "]="
                    + active);
        }
        return active;
    }

    /**
     * Returns the number of messages in the cache.
     *
     * @return the number of messages in the cache
     */
    public int getMessageCount() {
        return _handles.size();
    }

    /**
     * Determines if this cache can be destroyed. A <code>QueueDestinationCache</code>
     * can be destroyed if there are no active consumers and: <ul> <li>the queue
     * is persistent and there are no messages</li> <li> the queue is temporary
     * and the corresponding connection is closed </li> </ul>
     *
     * @return <code>true</code> if the cache can be destroyed, otherwise
     *         <code>false</code>
     */
    public boolean canDestroy() {
        boolean destroy = false;
        if (!hasConsumers()) {
            JmsDestination queue = getDestination();
            if (queue.getPersistent() && getMessageCount() == 0) {
                destroy = true;
            } else if (queue.isTemporaryDestination()) {
                // check if there is a corresponding connection. If
                // not, it has been closed, and the cache can be removed
                long connectionId =
                        ((JmsTemporaryDestination) queue).getConnectionId();
                if (_connections.getConnection(connectionId) == null) {
                    destroy = true;
                }
            }
        }
        return destroy;
    }

    /**
     * Destroy this object.
     */
    public void destroy() {
        super.destroy();
        _browsers.clear();
    }

    /**
     * Initialise the cache. This removes all the expired messages, and then
     * retrieves all unacked messages from the database and stores them
     * locally.
     *
     * @throws JMSException if the cache can't be initialised
     */
    protected void init() throws JMSException {
        JmsDestination queue = getDestination();

        List handles;
        DatabaseService service = null;
        try {
            service = DatabaseService.getInstance();
            Connection connection = service.getConnection();
            service.getAdapter().removeExpiredMessageHandles(connection,
                    queue.getName());
            handles = service.getAdapter().getMessageHandles(connection, queue,
                    queue.getName());
        } catch (PersistenceException exception) {
            _log.error(exception, exception);
            try {
                if (service != null) {
                    service.rollback();
                }
            } catch (PersistenceException error) {
                _log.error(error, error);
            }
            throw new JMSException(exception.getMessage());
        }

        Iterator iterator = handles.iterator();
        DefaultMessageCache cache = getMessageCache();
        while (iterator.hasNext()) {
            PersistentMessageHandle handle = (PersistentMessageHandle) iterator.next();
            String messageId = handle.getMessageId();
            MessageRef reference = cache.getMessageRef(messageId);
            if (reference == null) {
                reference = new CachedMessageRef(messageId, true, cache);
            }
            cache.addMessageRef(reference);
            handle.reference(reference);
            handle.setDestinationCache(this);
            _handles.add(new QueueConsumerMessageHandle(handle));

            checkMessageExpiry(reference, handle.getExpiryTime());
        }
    }

    /**
     * Add a message, and notify any listeners.
     *
     * @param reference a reference to the message
     * @param message   the message
     * @param handle    the handle to add
     * @throws JMSException for any error
     */
    protected void addMessage(MessageRef reference, MessageImpl message,
                              MessageHandle handle) throws JMSException {
        addMessage(reference, message);
        _handles.add(handle);

        // notify any queue listeners that a message has arrived
        notifyQueueListeners(handle, message);

        // create a lease iff one is required
        checkMessageExpiry(reference, message);
    }


    /**
     * Notify queue browsers that a message has arrived.
     *
     * @param handle  a handle to the message
     * @param message the message
     * @throws JMSException if a browser fails to handle the message
     */
    protected void notifyQueueListeners(MessageHandle handle,
                                        MessageImpl message)
            throws JMSException {
        QueueBrowserEndpoint[] browsers =
                (QueueBrowserEndpoint[]) _browsers.toArray(
                        new QueueBrowserEndpoint[0]);

        for (int index = 0; index < browsers.length; ++index) {
            QueueBrowserEndpoint browser = browsers[index];
            browser.messageAdded(handle, message);
        }
    }

    /**
     * Remove an expired non-peristent message, and notify any listeners.
     *
     * @param reference the reference to the expired message
     * @throws JMSException for any error
     */
    protected void messageExpired(MessageRef reference) throws JMSException {
        _handles.remove(reference.getMessageId());
        // @todo - notify browser
        super.messageExpired(reference);
    }

    /**
     * Remove an expired persistent message, and notify any listeners.
     *
     * @param reference the reference to the expired message
     * @throws JMSException         if a listener fails to handle the
     *                              expiration
     * @throws PersistenceException if there is a persistence related problem
     */
    protected void persistentMessageExpired(MessageRef reference)
            throws JMSException, PersistenceException {
        _handles.remove(reference.getMessageId());
        // @todo - notify browsers
        super.messageExpired(reference);
    }

    /**
     * Return the next QueueConsumerEndpoint that can consume the specified
     * message or null if there is none.
     *
     * @param message - the message to consume
     * @return the consumer who should receive this message, or null
     */
    private ConsumerEndpoint getConsumerForMessage(MessageImpl message) {
        ConsumerEndpoint result = null;

        ConsumerEndpoint[] consumers = getConsumerArray();
        final int size = consumers.length;
        if (size > 0) {
            synchronized (_lock) {
                // roll over the consumer index if it is greater
                // than the number of registered consumers
                if ((_lastConsumerIndex + 1) > size) {
                    _lastConsumerIndex = 0;
                }

                // look over the list of consumers and return the
                // first endpoint that can process this message
                int index = _lastConsumerIndex;
                do {
                    ConsumerEndpoint consumer = consumers[index];
                    // if the endpoint has a message listener registered
                    // or the endpoint is waiting for a message and the
                    // message satisfies the selector then return it to
                    // the client.
                    if ((consumer.isAsynchronous()
                            || consumer.isWaitingForMessage())
                            && consumer.selects(message)) {
                        _lastConsumerIndex = ++index;
                        result = consumer;
                        break;
                    }

                    // advance to the next consumer
                    if (++index >= size) {
                        index = 0;
                    }
                } while (index != _lastConsumerIndex);
            }
        }

        return result;
    }

}