Class PollingTransport

java.lang.Object

com.codename1.backend.messaging.MessageTransport

com.codename1.backend.messaging.PollingTransport

All Implemented Interfaces:

Closeable, AutoCloseable

Direct Known Subclasses:

AmqpTransport, KafkaTransport, PubSubTransport, RedisStreamTransport, SqsTransport

public abstract class PollingTransport
extends MessageTransport

A transport whose consumers ask the broker for messages in a loop: the database, Redis Streams, Kafka. It runs each subscription's consumer threads, and turns a handler's failure into a later delivery or a dead letter, so a subclass only says how to poll, acknowledge and reschedule.

Consumer threads run as part of the server that subscribed, so a handler reaches that server's beans, data source and key/value store.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
protected static final class	PollingTransport.Delivery	One message as polled, with whatever the broker needs to acknowledge it.

Field Summary

Fields

Modifier and Type	Field	Description
protected final RetryPolicy	retry	The retry policy of every subscription.

Constructor Summary

Constructors

Modifier	Constructor	Description
protected	PollingTransport(RetryPolicy retry)	A transport retrying by retry.

Method Summary

Modifier and Type	Method	Description
protected abstract void	ack(String destination, String group, PollingTransport.Delivery delivery)	Acknowledges a handled delivery.
protected void	deadLetter(String destination, String group, PollingTransport.Delivery delivery, String error)	Sends delivery to the dead-letter destination and acknowledges it.
protected static Message	identified(Message message, String id)	message, given the identifier the broker knows it by.
protected static boolean	notYet(Message message, long now)	Whether message carries a retry time still in the future.
protected abstract List<PollingTransport.Delivery>	poll(String destination, String group, int max, long waitMillis)	Up to max messages of destination for group, waiting up to waitMillis for the first; an empty list when none came.
protected void	redeliver(String destination, String group, PollingTransport.Delivery delivery, int attempt, long notBefore)	Has delivery delivered again, as attempt, no sooner than notBefore.
protected void	stopSubscriptions()	Stops every subscription, waiting for the messages being handled.
Subscription	subscribe(String destination, String group, int concurrency, MessageHandler handler)	Starts concurrency consumers of destination in group.

Methods inherited from class MessageTransport

close, getName, isHealthy, isTransactional, send

Methods inherited from class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

retry

protected final RetryPolicy retry

The retry policy of every subscription.

Constructor Details

PollingTransport

protected PollingTransport(RetryPolicy retry)

A transport retrying by retry.

Method Details

poll

protected abstract List<PollingTransport.Delivery> poll(String destination,
 String group,
 int max,
 long waitMillis)
                                                 throws IOException

Up to max messages of destination for group, waiting up to waitMillis for the first; an empty list when none came.

Throws:

IOException

ack

protected abstract void ack(String destination,
 String group,
 PollingTransport.Delivery delivery)
                     throws IOException

Acknowledges a handled delivery.

Throws:

IOException

redeliver

protected void redeliver(String destination,
 String group,
 PollingTransport.Delivery delivery,
 int attempt,
 long notBefore)
                  throws IOException

Has delivery delivered again, as attempt, no sooner than notBefore. The default sends a copy carrying the attempt and the time in its headers and acknowledges the original; a consumer that polls the copy early puts it back with notYet(Message, long).

Throws:

IOException

deadLetter

protected void deadLetter(String destination,
 String group,
 PollingTransport.Delivery delivery,
 String error)
                   throws IOException

Sends delivery to the dead-letter destination and acknowledges it.

Throws:

IOException

identified

protected static Message identified(Message message,
 String id)

message, given the identifier the broker knows it by.

notYet

protected static boolean notYet(Message message,
 long now)

Whether message carries a retry time still in the future.

subscribe

public Subscription subscribe(String destination,
 String group,
 int concurrency,
 MessageHandler handler)
                       throws IOException

Description copied from class: MessageTransport

Starts concurrency consumers of destination in group.

• group: subscriptions of one group share the messages between them, and each group sees every message -- on a transport with groups (Redis Streams, Kafka, AMQP through one queue per group). On memory: and db: a destination is a queue and every subscription competes for it.

Specified by:

subscribe in class MessageTransport

Throws:

IOException

stopSubscriptions

protected void stopSubscriptions()

Stops every subscription, waiting for the messages being handled.