CSC310 Lecture 13

MQTT
(2026-11-03)

1. CSC 3100 Fundamentals of Software Engineering Lecture 13. MQTT Broker Dr. Javier Gonzalez-Sanchez javiergs@calpoly.edu www.javiergs.phd ffi o ce: 14 -227
2. What we already know • Cl sses nd interf ces de ine responsibilities • UML describes structure before implement tion • Observer noti ies interested objects • Str tegy ch nges beh vior without ch nging client • J v code should re lect the design a a a a a f a a a f a a f a a a a a a • Next: How do sep r te pplic tions communic te?
3. Pong https://github.com/CSC3100/Pong-Game
4. Game
5. Chat Remote: Local: ABC Remote: ABC Local:
6. MQTT Broker
7. Message Queuing
8. Vocabulary • Broker: server th t routes published mess ges • Client: pplic tion th t publishes nd/or subscribes • Topic: n med mess ge ch nnel, e.g., ex mple/toRe d • P ylo d: d t sent with public tion • Subscribe: express interest in topic a a a a a a a a a a a a a a a a a a 08
9. Coding
10. Eclipse Paho for Java Wh t is Eclipse P ho? • A set of MQTT client libr ries developed by the Eclipse Found tion. • It supports multiple l ngu ges, such s J v , Python, J v Script, etc. J v Dependency (M ven) a a a a a a a a a a a a a a <dependency> <groupId>org.eclipse.paho</groupId> <artifactId>org.eclipse.paho.client.mqttv3</artifactId> <version>1.2.5</version> </dependency>
11. Classes Main - BROKER_URL: String - TOPICS: String[] + main(String[]): void Subscriber - broker: String; - topics: String[] + Subscriber(String, String[]) + run(): void + connectionLost(Throwable): void + messageArrived(String, MqttMessage): void + deliveryComplete(IMqttDeliveryToken): void Publisher - broker: String; - topics: String[] + Publisher(String, String[]) + run(): void «interface» Runnable + run(): void MqttClient + connect(); + subscribe(...) + publish(...); + disconnect() «interface» MqttCallback + connectionLost(...) + messageArrived(...); + deliveryComplete(...)
12. https://github.com/CSC3100/MQTT
13. Quality-of-service options • 0 – "at most once": A.K.A. "fire-and-forget." This option is suitable when message loss is acceptable, as it doesn't require acknowledgment or persistence. • 1 – "at least once": This option should be chosen when message loss is unacceptable, and your subscribers can handle duplicate messages. • 2 – "Exactly once": This option is ideal when message loss is unacceptable, and your subscribers cannot handle duplicate messages.
14. https://github.com/CSC3100/MQTT
15. Questions
16. CSC 3100 Fundamentals of Software Engineering Javier Gonzalez-Sanchez, Ph.D. javiergs@calpoly.edu Fall 2026 Copyright Notice. These slides are provided exclusively for educational use in CSC 3100 within the California State University system. Redistribution or use for any other purpose is prohibited without prior written permission.