Consumer

The Alpakka JMS connector offers consuming JMS messages from topics or queues:

• Read javax.jms.Messages from an Akka Streams source
• Allow for client acknowledgement to the JMS broker
• Allow for JMS transactions
• Read raw JVM types from an Akka Streams Source

The JMS message model supports several types of message bodies in (see javax.jms.Message), which may be created directly from the Akka Stream elements, or in wrappers to access more advanced features.

Receiving messages

JmsConsumerJmsConsumer offers factory methods to consume JMS messages in a number of ways.

This examples shows how to listen to a JMS queue and emit javax.jms.Message elements into the stream.

The materialized value JmsConsumerControlJmsConsumerControl is used to shut down the consumer (it is a KillSwitchKillSwitch) and offers the possibility to inspect the connectivity state of the consumer.

Scala

copysourceval jmsSource: Source[javax.jms.Message, JmsConsumerControl] = JmsConsumer(
  JmsConsumerSettings(system, connectionFactory).withQueue("numbers")
)

val (control, result): (JmsConsumerControl, Future[immutable.Seq[String]]) =
  jmsSource
    .take(msgsIn.size)
    .map {
      case t: javax.jms.TextMessage => t.getText
      case other => sys.error(s"unexpected message type ${other.getClass}")
    }
    .toMat(Sink.seq)(Keep.both)
    .run()

control.shutdown()

Java

copysourceConnectionFactory connectionFactory = server.createConnectionFactory();

Source<javax.jms.Message, JmsConsumerControl> jmsSource =
    JmsConsumer.create(
        JmsConsumerSettings.create(system, connectionFactory).withQueue("test"));

Pair<JmsConsumerControl, CompletionStage<List<String>>> controlAndResult =
    jmsSource
        .take(expectedMessages)
        .map(
            msg -> {
              if (msg instanceof TextMessage) {
                TextMessage t = (TextMessage) msg;
                return t.getText();
              } else
                throw new RuntimeException("unexpected message type " + msg.getClass());
            })
        .toMat(Sink.seq(), Keep.both())
        .run(system);

JmsConsumerControl control = controlAndResult.first();
control.shutdown();

Configure JMS consumers

To connect to the JMS broker, first define an appropriate javax.jms.ConnectionFactory. The Alpakka tests and all examples use Active MQ.

Scala

copysourceval connectionFactory: javax.jms.ConnectionFactory = new org.apache.activemq.ActiveMQConnectionFactory(url)

Java

copysourcejavax.jms.ConnectionFactory connectionFactory = server.createConnectionFactory();

The created ConnectionFactory is then used for the creation of the different JMS sources.

The JmsConsumerSettingsJmsConsumerSettings factories allow for passing the actor system to read from the default alpakka.jms.consumer section, or you may pass a Config instance which is resolved to a section of the same structure.

Scala

copysourceval consumerConfig: Config = system.settings.config.getConfig(JmsConsumerSettings.configPath)
// reiterating defaults from reference.conf
val settings = JmsConsumerSettings(consumerConfig, connectionFactory)
  .withQueue("target-queue")
  .withCredentials(Credentials("username", "password"))
  .withConnectionRetrySettings(retrySettings)
  .withSessionCount(1)
  .withBufferSize(100)
  .withAckTimeout(1.second)

Java

copysourceConfig consumerConfig = config.getConfig(JmsConsumerSettings.configPath());
JmsConsumerSettings settings =
    JmsConsumerSettings.create(consumerConfig, new ActiveMQConnectionFactory("broker-url"))
        .withTopic("message-topic")
        .withCredentials(Credentials.create("username", "password"))
        .withConnectionRetrySettings(retrySettings)
        .withSessionCount(10)
        .withAcknowledgeMode(AcknowledgeMode.AutoAcknowledge())
        .withSelector("Important = TRUE");

The Alpakka JMS consumer is configured via default settings in the HOCON config file section alpakka.jms.consumer in your application.conf, and settings may be tweaked in the code using the withXyz methods. On the second tab the section from reference.conf shows the structure to use for configuring multiple set-ups.

Table

Setting	Description	Default Value
connectionFactory	Factory to use for creating JMS connections	Must be set in code
destination	Destination (queue or topic) to send JMS messages to	Must be set in code
credentials	JMS broker credentials	Empty
connectionRetrySettings	Retry characteristics if the connection failed to be established or is taking a long time.	See Connection Retries
sessionCount	Number of parallel sessions to use for receiving JMS messages.	defaults to 1
bufferSize	Maximum number of messages to prefetch before applying backpressure.	100
ackTimeout	For use with JMS transactions, only: maximum time given to a message to be committed or rolled back.	1 second
maxAckInterval	For use with AckSource, only: The max duration before the queued acks are sent to the broker	Empty
maxPendingAcks	For use with AckSource, only: The amount of acks that get queued before being sent to the broker	100
selector	JMS selector expression (see below)	Empty
connectionStatusSubscriptionTimeout	5 seconds	Time to wait for subscriber of connection status events before starting to discard them

reference.conf

copysource# Jms Consumer Settings
# sets default values
consumer {
  # Configure connection retrying by providing settings for ConnectionRetrySettings.
  connection-retry = ${alpakka.jms.connection-retry}
  # Credentials to connect to the JMS broker.
  # credentials {
  #   username = "some text"
  #   password = "some text"
  # }
  # "off" to not use any credentials.
  credentials = off
  # Number of parallel sessions to use for receiving JMS messages.
  session-count = 1
  # Buffer size for maximum number for messages read from JMS when there is no demand.
  buffer-size = 100
  # JMS selector expression.
  # See https://docs.oracle.com/cd/E19798-01/821-1841/bncer/index.html
  # empty string for unset
  selector = "" # optional
  # Set an explicit acknowledge mode.
  # (Consumers have specific defaults.)
  # See eg. javax.jms.Session.AUTO_ACKNOWLEDGE
  # Allowed values: "off", "auto", "client", "duplicates-ok", "session", integer value
  acknowledge-mode = off
  # Timeout for acknowledge.
  # (Used by TX consumers.)
  ack-timeout = 1 second
  # For use with transactions, if true the stream fails if Alpakka rolls back the transaction
  # when `ack-timeout` is hit.
  fail-stream-on-ack-timeout = false
  # Max interval before sending queued acknowledges back to the broker. (Used by AckSources.)
  # max-ack-interval = 5 seconds
  # Max number of acks queued by AckSource before they are sent to broker. (Unless MaxAckInterval is specified).
  max-pending-acks = ${alpakka.jms.consumer.buffer-size}
  # How long the stage should preserve connection status events for the first subscriber before discarding them
  connection-status-subscription-timeout = 5 seconds
}

Broker specific destinations

To reach out to special features of the JMS broker, destinations can be created as CustomDestination which takes a factory method for creating destinations.

Scala

copysourcedef createQueue(destinationName: String): Session => javax.jms.Queue = { (session: Session) =>
  val amqSession = session.asInstanceOf[ActiveMQSession]
  amqSession.createQueue(s"my-$destinationName")
}

val jmsSource: Source[javax.jms.Message, JmsConsumerControl] = JmsConsumer(
  JmsConsumerSettings(consumerConfig, connectionFactory)
    .withDestination(CustomDestination("custom", createQueue("custom")))
)

Java

copysourceFunction<javax.jms.Session, javax.jms.Destination> createQueue(String destinationName) {
  return (session) -> {
    ActiveMQSession amqSession = (ActiveMQSession) session;
    try {
      return amqSession.createQueue("my-" + destinationName);
    } catch (JMSException e) {
      throw new RuntimeException(e);
    }
  };
}

        Source<Message, JmsConsumerControl> jmsSource =
            JmsConsumer.create(
                JmsConsumerSettings.create(system, connectionFactory)
                    .withDestination(new CustomDestination("custom", createQueue("custom"))));

Using JMS client acknowledgement

Client acknowledgement ensures a message is successfully received by the consumer and notifies the JMS broker for every message. Due to the threading details in JMS brokers, this special source is required (see the explanation below).

Scala

copysourceval jmsSource: Source[AckEnvelope, JmsConsumerControl] = JmsConsumer.ackSource(
  JmsConsumerSettings(consumerConfig, connectionFactory)
    .withSessionCount(5)
    .withQueue(queueName)
)

val result: Future[immutable.Seq[javax.jms.Message]] =
  jmsSource
    .take(msgsIn.size)
    .map { ackEnvelope =>
      ackEnvelope.acknowledge()
      ackEnvelope.message
    }
    .runWith(Sink.seq)

Java

copysourceConnectionFactory connectionFactory = server.createConnectionFactory();

Source<akka.stream.alpakka.jms.AckEnvelope, JmsConsumerControl> jmsSource =
    JmsConsumer.ackSource(
        JmsConsumerSettings.create(system, connectionFactory)
            .withSessionCount(5)
            .withQueue("test"));

CompletionStage<List<javax.jms.Message>> result =
    jmsSource
        .take(msgsIn.size())
        .map(
            envelope -> {
              envelope.acknowledge();
              return envelope.message();
            })
        .runWith(Sink.seq(), system);

The sessionCount parameter controls the number of JMS sessions to run in parallel.

Notes:

• Using multiple sessions increases throughput, especially if acknowledging message by message is desired.
• Messages may arrive out of order if sessionCount is larger than 1.
• Message-by-message acknowledgement can be achieved by setting bufferSize to 0, thus disabling buffering. The outstanding messages before backpressure will be the sessionCount.
• If buffering is enabled then it’s possible for messages to remain in the buffer and never be acknowledged (or acknowledged after a long time) when no new elements arrive to reach the maxPendingAcks threshold. By setting maxAckInterval messages will be acknowledged after the defined interval or number of pending acks, whichever comes first.
• The default AcknowledgeMode is ClientAcknowledge but can be overridden to custom AcknowledgeModes, even implementation-specific ones by setting the AcknowledgeMode in the JmsConsumerSettings when creating the stream.

Using JMS transactions

JMS transactions may be used with this connector. Be aware that transactions are a heavy-weight tool and may not perform very good.

Scala

copysourceval jmsSource: Source[TxEnvelope, JmsConsumerControl] = JmsConsumer.txSource(
  JmsConsumerSettings(consumerConfig, connectionFactory)
    .withSessionCount(5)
    .withAckTimeout(1.second)
    .withQueue(queueName)
)

val result: Future[immutable.Seq[javax.jms.Message]] =
  jmsSource
    .take(msgsIn.size)
    .map { txEnvelope =>
      txEnvelope.commit()
      txEnvelope.message
    }
    .runWith(Sink.seq)

Java

copysourceConnectionFactory connectionFactory = server.createConnectionFactory();

Source<akka.stream.alpakka.jms.TxEnvelope, JmsConsumerControl> jmsSource =
    JmsConsumer.txSource(
        JmsConsumerSettings.create(system, connectionFactory)
            .withSessionCount(5)
            .withAckTimeout(Duration.ofSeconds(1))
            .withQueue("test"));

CompletionStage<List<javax.jms.Message>> result =
    jmsSource
        .take(msgsIn.size())
        .map(
            txEnvelope -> {
              txEnvelope.commit();
              return txEnvelope.message();
            })
        .runWith(Sink.seq(), system);

The sessionCount parameter controls the number of JMS sessions to run in parallel.

The ackTimeout parameter controls the maximum time given to a message to be committed or rolled back. If the message times out it will automatically be rolled back. This is to prevent stream from starvation if the application fails to commit or rollback a message, or if the message errors out and the stream is resumed by a decider.

Notes:

• Higher throughput is achieved by increasing the sessionCount.
• Messages will arrive out of order if sessionCount is larger than 1.
• Buffering is not supported in transaction mode. The bufferSize is ignored.
• The default AcknowledgeMode is SessionTransacted but can be overridden to custom AcknowledgeModes, even implementation-specific ones by setting the AcknowledgeMode in the JmsConsumerSettings when creating the stream.

Using JMS selectors

Create a javax.jms.Message source specifying a JMS selector expression: Verify that we are only receiving messages according to the selector:

Scala

copysourceval jmsSource = JmsConsumer(
  JmsConsumerSettings(consumerConfig, connectionFactory)
    .withQueue("numbers")
    .withSelector("IsOdd = TRUE")
)

Java

copysourceSource<Message, JmsConsumerControl> jmsSource =
    JmsConsumer.create(
        JmsConsumerSettings.create(system, connectionFactory)
            .withQueue("test")
            .withSelector("IsOdd = TRUE"));

Raw JVM type sources

Text sources

The textSource emits the received message body as String:

Scala

copysourceval connectionFactory: javax.jms.ConnectionFactory = new org.apache.activemq.ActiveMQConnectionFactory(url)
val jmsSource: Source[String, JmsConsumerControl] = JmsConsumer.textSource(
  JmsConsumerSettings(system, connectionFactory).withQueue("test")
)

val result: Future[immutable.Seq[String]] = jmsSource.take(in.size).runWith(Sink.seq)

Java

copysourcejavax.jms.ConnectionFactory connectionFactory = server.createConnectionFactory();
Source<String, JmsConsumerControl> jmsSource =
    JmsConsumer.textSource(
        JmsConsumerSettings.create(system, connectionFactory).withQueue("test"));

CompletionStage<List<String>> result =
    jmsSource.take(in.size()).runWith(Sink.seq(), system);

Byte array sources

The bytesSource emits the received message body as byte array:

Scala

copysourceval jmsSource: Source[Array[Byte], JmsConsumerControl] = JmsConsumer.bytesSource(
  JmsConsumerSettings(system, connectionFactory).withQueue("test")
)

val result: Future[Array[Byte]] =
  jmsSource
    .take(1)
    .runWith(Sink.head)

Java

copysourceConnectionFactory connectionFactory = server.createConnectionFactory();

Source<byte[], JmsConsumerControl> jmsSource =
    JmsConsumer.bytesSource(
        JmsConsumerSettings.create(system, connectionFactory).withQueue("test"));

CompletionStage<byte[]> result = jmsSource.take(1).runWith(Sink.head(), system);

Map sources

The mapSource emits the received message body as Map[String, Object]Map<String, Object>:

Scala

copysourceval jmsSource: Source[Map[String, Any], JmsConsumerControl] = JmsConsumer.mapSource(
  JmsConsumerSettings(system, connectionFactory).withQueue("test")
)

val result: Future[immutable.Seq[Map[String, Any]]] =
  jmsSource
    .take(1)
    .runWith(Sink.seq)

Java

copysourceConnectionFactory connectionFactory = server.createConnectionFactory();

Source<Map<String, Object>, JmsConsumerControl> jmsSource =
    JmsConsumer.mapSource(
        JmsConsumerSettings.create(system, connectionFactory).withQueue("test"));

CompletionStage<Map<String, Object>> resultStage =
    jmsSource.take(1).runWith(Sink.head(), system);

Object sources

The objectSource emits the received message body as deserialized JVM instance. As serialization may be a security concern, JMS clients require special configuration to allow this. The example shows how to configure ActiveMQ connection factory to support serialization. See ActiveMQ Security for more information on this.

Scala

copysourceval connectionFactory = connFactory.asInstanceOf[ActiveMQConnectionFactory]
connectionFactory.setTrustedPackages(List(classOf[DummyObject].getPackage.getName).asJava)
val jmsSource: Source[java.io.Serializable, JmsConsumerControl] = JmsConsumer.objectSource(
  JmsConsumerSettings(system, connectionFactory).withQueue("test")
)

val result: Future[java.io.Serializable] =
  jmsSource
    .take(1)
    .runWith(Sink.head)

Java

copysourceActiveMQConnectionFactory connectionFactory =
    (ActiveMQConnectionFactory) server.createConnectionFactory();
connectionFactory.setTrustedPackages(
    Arrays.asList(DummyJavaTests.class.getPackage().getName()));

Source<java.io.Serializable, JmsConsumerControl> jmsSource =
    JmsConsumer.objectSource(
        JmsConsumerSettings.create(system, connectionFactory).withQueue("test"));

CompletionStage<java.io.Serializable> result =
    jmsSource.take(1).runWith(Sink.head(), system);

Request / Reply

The request / reply pattern can be implemented by streaming a JmsConsumerJmsConsumer to a JmsProducerJmsProducer, with a stage in between that extracts the ReplyTo and CorrelationID from the original message and adds them to the response.

Scala

copysourceval respondStreamControl: JmsConsumerControl =
  JmsConsumer(JmsConsumerSettings(system, connectionFactory).withQueue("test"))
    .collect {
      case message: TextMessage => JmsTextMessage(message)
    }
    .map { textMessage =>
      textMessage.headers.foldLeft(JmsTextMessage(textMessage.body.reverse)) {
        case (acc, rt: JmsReplyTo) => acc.to(rt.jmsDestination)
        case (acc, cId: JmsCorrelationId) => acc.withHeader(cId)
        case (acc, _) => acc
      }
    }
    .via {
      JmsProducer.flow(
        JmsProducerSettings(system, connectionFactory).withQueue("ignored")
      )
    }
    .to(Sink.ignore)
    .run()

Java

copysourceJmsConsumerControl respondStreamControl =
    JmsConsumer.create(
            JmsConsumerSettings.create(system, connectionFactory).withQueue("test"))
        .map(JmsMessageFactory::create)
        .collectType(JmsTextMessage.class)
        .map(
            textMessage -> {
              JmsTextMessage m = JmsTextMessage.create(reverse.apply(textMessage.body()));
              for (JmsHeader h : textMessage.getHeaders())
                if (h.getClass().equals(JmsReplyTo.class))
                  m = m.to(((JmsReplyTo) h).jmsDestination());
                else if (h.getClass().equals(JmsCorrelationId.class)) m = m.withHeader(h);
              return m;
            })
        .via(
            JmsProducer.flow(
                JmsProducerSettings.create(system, connectionFactory)
                    .withQueue("ignored")))
        .to(Sink.ignore())
        .run(system);