Slides for my Workshop on Event Driven Programming & Architecture. Held at Softwerkskammer Munich 2017-11-28 in the CodeCentric Office

1. Event-driven Programming
& Architecture
@MarcoEmrich Softwerkskammer Munich Dec. 2017

2. Sixsteps.com

3. Where?

4. GUI
https://www.flickr.com/photos/joris/2410290034

5. https://www.flickr.com/photos/11319126@N00/8270409318/in/photostream

6. Architecture

7. Microservices
http://martinfowler.com/articles/microservices.html

8. Evented-SOA

9. Domain Driven Design

10. Hexagonal Architecture

11. Hexagonal Architecture
Domain
Model

12. Hexagonal Architecture
Domain
Model
Adapter Adapter
Adapter
Adapter
Adapter
Adapter
Adapter
Adapter

13. Hexagonal Architecture
Domain
Model
Adapter Adapter
Adapter
Adapter
Adapter
Adapter
Adapter
Persistance
Adapter

14. Hexagonal Architecture
Domain
Model
Adapter Adapter
Adapter
Adapter
Adapter
Adapter
Adapter
Persistance
Adapter
GUI

15. Hexagonal Architecture
Domain
Model
Adapter Adapter
Adapter
Adapter
Adapter
Adapter
Adapter
Persistance
Adapter
GUI
Events
Events
Events
Events

16. Event Storming

17. What do you mean by
“Event-Driven”?
Martin Fowler
Event Notification
Event-Carried State Transfer
Event Sourcing
CQRS
https://martinfowler.com/articles/201701-event-driven.html

18. General
Programming-Model

19. Method
vs.
Event https://www.flickr.com/photos/gen/325927418

20. Sender Receiver
Message
Method Call

21. Sender Receiver
Listen
Raise Event
Event

22. Sender
ReceiverListen
Event
Raise Event Receiver
Listen
Receiver
Listen

23. https://www.flickr.com/photos/caroslines/547184477
Wiring

24. Sender
Receiver
Listen
Raise Event
Receiver
Listen
ReceiverListen
Sender
Raise Event
Observer

25. Sender
Receiver
Listen
Raise Event
Receiver
Listen
Receiver
Listen
Event-BUS
Pub/Sub

26. Event vs. Method
Method
Sender tells
Receiver
Sync
Fixed Coupling
New Receiver:
change to Sender
Event
Receiver listens to
Sender
Sync / Async
Loose Coupling
New Receiver:
no change to Sender
Sometimes: Hard to
Test/Debug

27. Testing?

28. Winner?
https://www.flickr.com/photos/48424574@N07/5096035675

29. We want
you for
Kata

30. http://udoncrew.deviantart.com/art/UFS-Impossible-Contortion-109860059
Try Extremes

31. TDD

32. Pair-Programming
https://www.youtube.com/watch?v=8wUOUmeulNs © 2012 Atlassian

33. Callcenter Kata

34. 0911/123499
040/45678
0171/3456789
….
Phone Number /
Caller ID

35. 0911/123499
040/45678
0171/3456789
….
Phone Number /
Caller ID
0911 Nürnberg
040
H
am
burg
0911/123499
….
040/45678
….

36. 0911/123499
040/45678
0171/3456789
….
Phone Number /
Caller ID
0911 Nürnberg
0911/123499
….
040/45678
….
Statistik
040
H
am
burg

37. callAgency
localCallcenter
„Berlin“
030/12345
Incoming Call
040/12345
030/12345
...
localCallcenter
„Hamburg“
040/12345
statistic
Pure OO
statistic
statistic

38. Constraints
Method-communication
no Events
Small Classes (SRP)
max. 20-30 LOC
max. 5 Methods

39. GO

40. Event Frameworks
https://www.flickr.com/photos/alebaffa/8939535066

41. Do It Yourself

42. Sender
Receiver
Listen
emit Event
Receiver
Listen
Receiver
Listen
Event-BUS
Pub/Sub

43. Minimal EventFramework
Event
name:String
payload:Object
Bus
emit(event)
addListener(eventName listener)،
ASender
AReceiver_2
listen_1()
listen_2()
AReceiver_1
listen_1()
listen_2()

44. public class Event {
private String name;
private Object payload;
public Event(String name, Object payload) {
this.name = name;
this.payload = payload;
}
public Event(String name) {
this.name = name;
}
public String getName() {
return name;
}
public Object getPayload() {
return payload;
}
}
Event (Java)

45. public class ReceiverDemo implements EventListener {
public void receive(Event event) {}
…
}
EventBus bus = new EventBus();
ReceiverDemo receiver1 = new ReceiverDemo();
ReceiverDemo receiver2 = new ReceiverDemo();
bus.addListener("SomethingHappened", receiver1);
bus.addListener("SomethingHappened", receiver2);
bus.emit(new Event("SomethingHappened"));
Basics (Java)

46. public class ReceiverDemo implements EventListener {
public void receive(Event event) {}
…
}
int payload = 27;
EventBus bus = new EventBus();
ReceiverDemo receiver1 = new ReceiverDemo();
bus.addListener("SomethingHappened", receiver1);
bus.emit(new Event("SomethingHappened", payload));
Payload (Java)

47. Basics (JS)
var callback1 = function() { … }
var callback2 = function() { … }
bus.addListener('SomethingHappened', callback1);
bus.addListener('SomethingHappened', callback2);
bus.emit('SomethingHappened');

48. Payload (JS)
var callback = function(payload) {
...
});
bus.addListener('SomethingHappened', callback);
bus.emit('SomethingHappened', {bar: 'foo'});

49. Tests/Specs
1) a_Bus_can_emit_Events
2) a_Receiver_gets_notified
3) multiple_Recivers_get_notified
4) Events_accept_a_Payload

50. GO

51. Callcenter Kata

52. Constraints
no Method-communication,
Events only

53. Constraints
no Method-communication,
Events only
Small Classes (SRP)
max. 20-30 LOC
max. 5 Methods