I am implementing MQTT Client with Eclipse Paho and has some problems:
Both Publisher and Subscriber connect to broker with qos = 1 and setCleanSession =
false.
My flow:
Connect Subscriber and Publisher to broker, it's ok.
Disconnect Subscriber (I force stop My Project which include Subscriber ), Publisher continuing publishing message.
Reconnect Subscriber -> it cannot connect and throw exception: connectionLost.
If i set qos of Subscriber = 0, it not throw exception but The client does not receive messages sent by the publisher while the subscriber is offline, which I do not want
Can someone help me with this?
This is my code in subcriber
try {
// Create an Mqtt client
MqttAsyncClient mqttClient
= new MqttAsyncClient("tcp://" + swmConfig.getMqttApiLink(), "MeasureTransactionApi");
// new MqttAsyncClient(serverURI, clientId, persistence)
MqttConnectOptions connOpts = new MqttConnectOptions();
connOpts.setUserName(swmConfig.getMqttUsername());
connOpts.setPassword(swmConfig.getMqttPassword().toCharArray());
connOpts.setCleanSession(false);
// Connect to RabbitMQ Broker
log.info("Connecting to RabbitMQ broker: " + swmConfig.getMqttApiLink());
IMqttToken conToken = mqttClient.connect(connOpts);
conToken.waitForCompletion(10000);
if (!conToken.isComplete() || conToken.getException() != null) {
log.info("Error connecting: " + conToken.getException());
System.exit(-1);
}
log.info("Connected");
// Latch used for synchronizing b/w threads
final CountDownLatch latch = new CountDownLatch(1);
// Callback - Anonymous inner-class for receiving messages
mqttClient.setCallback(new MqttCallback() {
public void messageArrived(String topic, MqttMessage message) {
String time = new Timestamp(System.currentTimeMillis()).toString();
log.info("\nReceived a Message from RabbitMQ Broker" + "\n\tTime: " + time
+ "\n\tTopic: " + topic + "\n\tMessage: "
+ new String(message.getPayload()) + "\n\tQoS: "
+ message.getQos() + "\n");
handleMQTTMessageService.handleMessageArrived(message);
}
public void connectionLost(Throwable cause) {
log.info("Connection to RabbitMQ broker lost!" + cause.getMessage());
latch.countDown();
}
public void deliveryComplete(IMqttDeliveryToken token) {
log.info("deliveryComplete");
}
});
// Subscribe client to the topic filter with QoS level of 1
log.info("Subscribing client to topic: " + topic);
IMqttToken subToken = mqttClient.subscribe(topic, 1);
subToken.waitForCompletion(10000);
if (!subToken.isComplete() || subToken.getException() != null) {
log.info("Error subscribing: " + subToken.getException());
System.exit(-1);
}
} catch (MqttException me) {
log.error("Error:", me);
}
QOS is independent for publishers and subscribers.
To ensure delivery to the subscribing client you need to subscribe at greater than QOS 0.
What happens to QOS 0 subscriptions depends on the broker, by default most will not queue messages for QOS 0 subscriptions, but mosquitto can be forced to with the queue_qos0_messages configuration flag
Related
I have deployed my Java-MDB based application using ActiveMQ as messaging service . I could see that a few messages have been in pending status for quite some time on some queues. I have read that this happens when ActiveMQ delivers the message and consumer consumes the message but doesn't send the ack back. But I could not see any related loggers on the consumer/application side which proves that the message is consumed.
Could anyone please help me understand the reason of message being stuck in pending state.
Edit - Adding the details:
We are using Auto-acknowledge as acknowledgeMode and below is the onMessage method used on consumer side.
public void onMessage(Message message) {
try {
// Clear all ThreadLocal in SQLQueryHelper.
SQLQueryHelper.clearCache();
String messageOut = processMessage(message);
// if there is a reply, send it out
if (messageOut != null) {
logger.warn(LoggerKeys.LOG_1_ARGS,
new String[] {"Reply from MDB not supported. " + messageOut});
}
} catch (Throwable e) {
logger.error(LoggerKeys.LOG_1_ARGS,
new String[] {"Error encountered: " + e.toString()});
try {
//put message on error queue
handleError(message, e);
} catch (Throwable e2) {
//retry to put message on error queue
handleErrorAndRollBack(message, e2);
}
}
}
We are building a project in Java which is using MQTT to communicate with other services using Paho client library. While running the application, I observed that if the broker is down, Paho is not caching failed outbound messages.
Is there a way to make Paho cache failed outbound messages?
I am using Paho version 1.2.5
org.eclipse.paho:org.eclipse.paho.client.mqttv3:1.2.5
Here is how I have configured it:
public void connect(MqttCallback mqttCallback, int maxInflight) {
try {
persistence = new MqttDefaultFilePersistence(mqttPersistenceLocation);
mqttClient = new MqttAsyncClient(broker, clientId, persistence);
connOpts = new MqttConnectOptions();
// always set cleanSession to false if QoS 1 or 2 is used.
connOpts.setCleanSession(false);
connOpts.setAutomaticReconnect(true);
connOpts.setMaxInflight(maxInflight);
mqttClient.setCallback(mqttCallback);
LOGGER.info("Connecting to broker: " + broker + " with maxInflight: " + maxInflight);
mqttClient.connect(connOpts).waitForCompletion();
LOGGER.info("Connected");
} catch (Exception e) {
LOGGER.error("Error while connecting to MQTT:" + e);
}
}
I've used the subscriber example from the google documentation for Google PubSub
the only modification I've made is commenting out the acknowledgement of the messages.
The subscriber doesn't add messages to the queue anymore while messages should be resent according to the interval set in the google cloud console.
Why is this happening or am I missing something?
public class SubscriberExample {
use the default project id
private static final String PROJECT_ID = ServiceOptions.getDefaultProjectId();
private static final BlockingQueue<PubsubMessage> messages = new LinkedBlockingDeque<>();
static class MessageReceiverExample implements MessageReceiver {
#Override
public void receiveMessage(PubsubMessage message, AckReplyConsumer consumer) {
messages.offer(message);
//consumer.ack();
}
}
/** Receive messages over a subscription. */
public static void main(String[] args) throws Exception {
// set subscriber id, eg. my-sub
String subscriptionId = args[0];
ProjectSubscriptionName subscriptionName = ProjectSubscriptionName.of(
PROJECT_ID, subscriptionId);
Subscriber subscriber = null;
try {
// create a subscriber bound to the asynchronous message receiver
subscriber = Subscriber.newBuilder(subscriptionName, new MessageReceiverExample()).build();
subscriber.startAsync().awaitRunning();
// Continue to listen to messages
while (true) {
PubsubMessage message = messages.take();
System.out.println("Message Id: " + message.getMessageId());
System.out.println("Data: " + message.getData().toStringUtf8());
}
} finally {
if (subscriber != null) {
subscriber.stopAsync();
}
}
}
}
When you do not acknowledge a messages, the Java client library calls modifyAckDeadline on the message until maxAckExtensionPeriod passes. By default, this value is one hour. Therefore, if you don't ack/nack the message or change this value, it is likely the message will not be redelivered for an hour. If you want to change the max ack extension period, set it on the builder:
subscriber = Subscriber.newBuilder(subscriptionName, new MessageReceiverExample())
.setMaxAckExtensionPeriod(Duration.ofSeconds(60))
.build();
It is also worth noting that when you don't ack or nack messages, then flow control may prevent the delivery of more messages. By default, the Java client library allows up to 1000 messages to be outstanding, i.e., waiting for ack or nack or for the max ack extension period to pass.
I have ActiveMQ running on the localhost using the default port, 61616. I put some messages in a Topic called topic.STUDENTS. I have a client program that I am trying to use to read the messages in the Topic. Here is the main part of the program that does not work as expected. I was expecting to get some of the message back but instead I just receive null.
public void receiveMessages() throws URISyntaxException, JMSException, Exception {
try {
//Create a ConnectionFactory
ActiveMQConnectionFactory connectionFactory = new ActiveMQConnectionFactory("tcp://localhost:61616");
//Create a Connection
Connection connection = connectionFactory.createConnection();
connection.start();
//Create a session
Session session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
//Create the destination (Topic or Queue)
Destination destination = session.createTopic("topic.STUDENTS");
//Create a MessageConsumer from the Session to the Topic or Queue
MessageConsumer consumer = session.createConsumer(destination);
//Wait for a message
Message message = consumer.receive(1000);
if (message instanceof TextMessage) {
TextMessage textMessage = (TextMessage) message;
String text = textMessage.getText();
System.out.println("Received: " + text);
} else {
System.out.println("Received: " + message);
}
consumer.close();
session.close();
connection.close();
} catch(Exception e) {
System.out.println("Caught: " + e);
e.printStackTrace();
}
}
This code basically apes the code from ActiveMQ 'Hello World' example: http://activemq.apache.org/hello-world.html
Does anyone know why I do not receive any messages from the Topic? Here is one message that is in the Topic that I can see through the ./activemq browse topic.STUDENTS command:
JMS_BODY_FIELD:JMSText = Invention-my-dear-friends-is-93%-perspiration-6%-electricity
JMS_HEADER_FIELD:JMSExpiration = 0
JMS_HEADER_FIELD:JMSMessageID = ID:user-thinkpad-335i-59919-1457977678059-1:1:1:1:3
JMS_HEADER_FIELD:JMSPriority = 4
JMS_HEADER_FIELD:JMSDestination = topic.STUDENTS
JMS_HEADER_FIELD:JMSTimestamp = 1457977678409
JMS_HEADER_FIELD:JMSRedelivered = false
JMS_HEADER_FIELD:JMSDeliveryMode = persistent
Topics do not retain messages by default, so if you start the consumer after you've produced the messages then any message that was sent before the consumer arrived is gone. If you want to consume messages that were produced while your consumer was offline then you need to use a Queue or register a durable Topic subscriber on the Topic prior to producing the messages.
I started JMS for a week now. I created JMS using Netbeans,maven and glassfish.
I have one producer and one durable consumer and I wanted to add another durable consumer to the same topic(not queue). Is it possible to do so?
because I want all the consumers consume all the message being sent by the producer whether the consumers are offline or not.
Any advice?
Thanks
public class DurableReceive {
#Resource(lookup = "jms/myDurableConnectionFactory")
private static ConnectionFactory connectionFactory;
#Resource(lookup = "jms/myNewTopic")
private static Topic topic;
public static void main(String[] args) {
Destination dest = (Destination) topic;
JMSConsumer consumer;
boolean messageReceived = false;
String message;
System.out.println("Waiting for messages...");
try (JMSContext context = connectionFactory.createContext();) {
consumer = context.createDurableConsumer(topic, "Subscriber1");
while (!messageReceived) {
message = consumer.receiveBody(String.class);
if (message != null) {
System.out.print("Received the following message: " + message);
System.out.println("(Received date: " + new Date() + ")\n");
} else {
messageReceived = true;
}
}
} catch (JMSRuntimeException e) {
System.err.println("##$%RuntimeException occurred: " + e.toString());
System.exit(1);
}
}
}
You can set different clientID for different durable consumers. Jms-broker uses combination of subscriptionName and clientId to identify the unique client (so if your subscriber have unique clientID - it can receive own messages). You can set clientID in your JmsContext.