Video and slides synchronized, mp3 and slide download available at URL http://bit.ly/2ww8DKs. Rossen Stoyanchev talks about five common use cases in web application development and explores the impact of building on Servlet and Reactive web application stacks. For reactive programming, he uses RxJava and Reactor. For the web stack, he pits Spring MVC vs Spring WebFlux allowing us to move easily between the Servlet and Reactive worlds and drawing a meaningful, apples-to-apples comparison. Filmed at qconnewyork.com. Rossen Stoyanchev is a Spring Framework committer at Pivotal in NYC. He is deeply involved in the Spring five effort to enable reactive programming models starting with a reactive foundation for web applications and extending to data, messaging, and more.

1. Rossen Stoyanchev
Servlet vs Reactive
5 use cases
stacks
in

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servlet-reactive-stack

3. Presented at QCon New York
www.qconnewyork.com
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4. Servlet Stack
● Servlet container
● Servlet API
● Spring MVC
Reactive Stack
● Netty, Servlet 3.1+, Undertow
● Reactive Streams
● Spring WebFlux

5. Reactive Spring
Reactive starters in Spring Boot 2.0
Spring Framework 5 WebFlux endpoints + reactive WebClient
Reactive Spring Data Kay repositories
Spring Security
and more…

6. Servlet Stack

7. FilterFilter Controller
Spring
MVC
Servlet API
container
thread
SERVLET STACK

8. Synchronous API
Filter, Servlet … void
SERVLET STACK

9. Blocking I/O
InputStream, OutputStream
SERVLET STACK

10. servletRequest.startAsync()
SERVLET STACK

11. Filter ControllerFilter Servlet
SERVLET STACKSERVLET STACK
Filter ControllerFilter Servlet
… do work or receive event + dispatch()…
container-
thread-1
container-
thread-2

12. Servlet API
Container
thread pool
Controller
SERVLET STACK
can use
reactive clients
Input & OutputStream
startAsync()

13. Concurrency
modelsConcurrencyConcurrencyConcurrency

14. “elastic”
thread pool
“parallel”
thread pool
100s, 1000s
waiting blocked threads
~ per CPU core
busy worker threads
Synchronous APIs Non-blocking code

15. What does it take to not block ?

16. event loop at the core

17. event driven architecture
message passing

18. means to compose async logic

19. bonus:
back pressure (a.k.a flow control)

20. Reactive Stack

21. Spring
WebFlux
Web
Filter
NO
BLOCKING
ANY
TIME
Controller
Reactive
Server
Adapter
Web
Filter
HTTP Server
Event Loop
REACTIVE
STACK

22. Asynchronous API
WebFilter, WebHandler…
Mono<Void>
REACTIVE
STACK

23. REACTIVE
STACK
Reactor Mono
Reactive Streams Publisher
0..1 elements

24. Non-blocking read:
Flux<DataBuffer> getBody()
REACTIVE
STACK

25. Non-blocking write:
writeWith(Flux<DataBuffer>)
REACTIVE
STACK

26. REACTIVE
STACK
Reactor Flux
Reactive Streams Publisher
0..N elements

27. request(1)
onNext(item)
Flux
Reactive Streams back pressure
request(1)
onNext(item)

28. request(n)
onNext(item)
FMonoEFluxDMonoCMonoB
Controller
Spring
WebFlux
WebFilter
Composition of async logic
MonoA
A B C
EF D
Actual processing
HTTP Server
Event Loop
REACTIVE
STACK

29. repository
Use Case #1
dataReactive

30. Demo

31. HTTP GET with reactive data repository
Designed to work on both Spring MVC and Spring WebFlux
Simply return reactive type (Flux, Observable) from @Controller

32. Flux<T>:
finite collection or infinite stream?

33. Use media type to decide

34. “application/json”
finite collection (JSON array)

35. No back pressure:
Flux#collectToList
(request all + buffer)

36. Use Case #2
back pressure
with
Response stream

37. “text/event-stream”,
“application/stream+json”
infinite stream

38. Back pressure:
request(n),
write, flush,
repeat

39. HTTP GET with streaming response
Simply return reactive type (Flux, Observable) from @Controller
Back pressure on Spring MVC and WebFlux

40. Servlet
Container
Servlet
API
Spring
MVC
Flux
Back pressure against blocking OutputStream
Controller Flux
Data
Repository
onNext(T)onNext(T)
Blocking write on
MvcAsync thread pool
request(n)request(1)
SERVLET STACK …

41. Servlet 3.1 non-blocking I/O ?
Unlike Servlet 3.0 async, Servlet 3.1 non-blocking is hard to retrofit
Requires deeper change
Mutually exclusive with rest of the Servlet API

42. HTTP
Server
Server
Adapter
Flux
Spring
WebFlux
Flux
Response streaming on reactive stack
Controller Flux
Data
Repo
onNext(T)onNext(T)onNext(T)
Non-blocking write
back pressure
to socket
request(n)request(n)request(n)

43. Demo

44. Use Case #3
remote service
orchestration
Reactive

45. Demo

46. Orchestrate non-blocking, nested remote service calls with ease
Similar to reactive data access
Spring MVC and Spring WebFlux
Reactive WebClient

49. Use Case #4
request inputReactive

50. Back pressure to socket
No reading until reactive demand signalled from upstream
Non-blocking
Reactive stack only territory !

51. HTTP POST with data
@RequestBody argument with reactive type (Mono, Single)
Reactive type is not required

52. Use Case #5
Data Ingestion
back pressure
with

53. Media type indicates infinite stream is expected
Non-blocking streaming + back pressure
HTTP POST with stream of data

54. HTTP
Server
Server
Adapter
Flux
Spring
WebFlux
Flux
Data ingestion on reactive stack
Controller
onNext(T)onNext(T)
Non-blocking read
back pressure
from socket
request(n)request(n)

55. Servlet stack summary
Reactive data repository
Streaming to the response with back pressure
Reactive orchestration of remote services
Reactive request input
Data ingestion with back pressure

56. Reactive stack summary
Reactive data repository
Streaming to the response with back pressure
Reactive orchestration of remote services
Reactive request input
Data ingestion with back pressure

57. Q & A
@rstoya05

58. Watch the video with slide synchronization on
InfoQ.com!
https://www.infoq.com/presentations/servlet-
reactive-stack