Synopsis

This project provides a simple example that shows how to use MQTT Paho Java 1.2.0 features of auto-reconnect and publish while offline. These features enhance the MQTT system high availability.

Motivation

This project is the base example from which interoperability with Solace message router high availability features of router redundancy and disaster recovery where tested.

Checking out and Building

This project depends on maven for building. To build the class locally, check out the project and build from source by doing the following:

git clone https://github.com/SolaceLabs/mqtt-3.1.1-test
cd /mqtt-3.1.1-test
mvn compile
  or
gradle build

Code Example

The interesting bits of code can be seen here, the initialize asyncClient, create host list with auto-reconnect and publish buffer:

public class SampleMqttClient implements MqttCallbackExtended {

connOpt = new MqttConnectOptions();
connOpt.setCleanSession(true);
connOpt.setKeepAliveInterval(30);
connOpt.setConnectionTimeout(60);
connOpt.setAutomaticReconnect(true);

String[] brokerList = new String[2];
brokerList[0] = BROKER_URL1;
brokerList[1] = BROKER_URL2;
connOpt.setServerURIs(brokerList);

DisconnectedBufferOptions bufferOpts = new DisconnectedBufferOptions();
bufferOpts.setBufferEnabled(true);
bufferOpts.setBufferSize(100);            // 100 message buffer
bufferOpts.setDeleteOldestMessages(true); // Purge oldest messages when buffer is full
bufferOpts.setPersistBuffer(false);       // Do not buffer to disk

try {
myClient = new MqttAsyncClient(brokerList[0], clientID, persistence);
myClient.setBufferOpts(bufferOpts);
myClient.setCallback(this);
            myClient.connect(connOpt);

Also there is a new callback on connection complete:

public void connectComplete(boolean reconnect, String serverURI) {
if (reconnect) {
System.out.println("Connection Reconnected! To: " + serverURI);
} else {
System.out.println("Initial Connection! To: " + serverURI);
}
addSubscriptions();
}

Tests

There are no tests with this project yet. Tests should be:

1. Publish before initial connection. Async MQTT client calls connect then publish before connectComplete() is called.

• Ensure message is stored as per persistent model then published once connection is established.

2. Cause reconnection. Once connected, disconnect the client at the message broker.

• Ensure the client reconnects, validate subscription still exists for Clean=0 and do not exist for clean=1.

3. Publish while reconnecting. Connect client, publish at a rate of ~20/sec. Disconnect client at the broker.

• Ensure reconnection and messages losslessly published in correct order.

4. Cause failover. Once connected, shut down access to connected MQTT router.

• Ensure failover to next broker in host list. Subscriptions should re-add as per clean flag.

Contributing

Please read CONTRIBUTING for details on our code of conduct, and the process for submitting pull requests to us.

Authors

See the list of contributors who participated in this project.

License

This project is licensed under the Apache License, Version 2.0. - See the LICENSE file for details.

Resources

For more information about working with Paho MQTT APIs:

• Eclipse PAho MQTT APIs

For more information about Solace technology in general please visit these resources:

• The Solace Developer Portal website at: http://dev.solace.com
• Understanding Solace technology.
• Ask the Solace community.