log.warn(cause, "Connection closed!");
}
}
);
final Channel channel = connection.createChannel();
channel.queueDeclare(queue, durable, exclusive, autoDelete, null);
channel.queueBind(queue, exchange, routingKey);
channel.addShutdownListener(
new ShutdownListener()
{
@Override
public void shutdownCompleted(ShutdownSignalException cause)
{
log.warn(cause, "Channel closed!");
}
}
);
// We create a QueueingConsumer that will not auto-acknowledge messages since that
// happens on commit().
final QueueingConsumer consumer = new QueueingConsumer(channel);
channel.basicConsume(queue, false, consumer);
return new Firehose()
{
/**
* Storing the latest delivery as a member variable should be safe since this will only be run
* by a single thread.
*/
private Delivery delivery;
/**
* Store the latest delivery tag to be able to commit (acknowledge) the message delivery up to
* and including this tag. See commit() for more detail.
*/
private long lastDeliveryTag;
@Override
public boolean hasMore()
{
delivery = null;
try {
// Wait for the next delivery. This will block until something is available.
delivery = consumer.nextDelivery();
if (delivery != null) {
lastDeliveryTag = delivery.getEnvelope().getDeliveryTag();
// If delivery is non-null, we report that there is something more to process.
return true;
}
}
catch (InterruptedException e) {
// A little unclear on how we should handle this.
// At any rate, we're in an unknown state now so let's log something and return false.
log.wtf(e, "Got interrupted while waiting for next delivery. Doubt this should ever happen.");
}
// This means that delivery is null or we caught the exception above so we report that we have
// nothing more to process.
return false;
}
@Override
public InputRow nextRow()
{
if (delivery == null) {
//Just making sure.
log.wtf("I have nothing in delivery. Method hasMore() should have returned false.");
return null;
}
return stringParser.parse(new String(delivery.getBody(), Charsets.UTF_8));
}
@Override
public Runnable commit()
{
// This method will be called from the same thread that calls the other methods of
// this Firehose. However, the returned Runnable will be called by a different thread.
//
// It should be (thread) safe to copy the lastDeliveryTag like we do below and then
// acknowledge values up to and including that value.
return new Runnable()
{
// Store (copy) the last delivery tag to "become" thread safe.
final long deliveryTag = lastDeliveryTag;
@Override
public void run()
{
try {
log.info("Acknowledging delivery of messages up to tag: " + deliveryTag);
// Acknowledge all messages up to and including the stored delivery tag.
channel.basicAck(deliveryTag, true);
}
catch (IOException e) {
log.error(e, "Unable to acknowledge message reception to message queue.");
}
}
};
}
@Override
public void close() throws IOException
{
log.info("Closing connection to RabbitMQ");
channel.close();
connection.close();
}
};
}