The document provides an introduction to Spring WebFlux, covering its architecture, reactive programming concepts, and practical application examples. It outlines the differences between non-blocking and blocking I/O, highlights the advantages and disadvantages, and demonstrates reactive streams using the Reactor library. The document also includes code snippets for implementing publishers and consumers using reactive programming techniques.

1. Por: Wellington
Macedo
Introdução à
Spring Web Flux
Por: Wellington
Vulgo: Lelim, Oesli
ou Jão

2. ● O que é Spring WebFlux?
● Reactive Programming
● Reactive Stream
○ Reactor
● Arquitetura do WebFlux
● Aplicação de Exemplo
● Non-blocking IO vs Blocking IO
● Event loop
● Vantagens
● Desvantagens
● Referências
Agenda

3. O que é Spring Web Flux
● É um projeto do Spring!
● Fornece suporte para programação reativa na camada Web do Spring
● Chegou na versão 5.0 do Spring (2017)
AH NÃO BRINCA WELLINGTON
😒

4. Reactive Programming
É um paradigma de programação

5. Reactive Programming
PUB/SUB

6. Reactive Programming
Vamos ver a aplicação rodando!

7. Reactive Programming
interface Consumer<T> {
fun consume(command: T)
}

8. Reactive Programming
class Publisher<T> {
private val consumers = mutableListOf<Consumer<T>>()
fun subscribe(consumer: Consumer<T>) {
consumers.add(consumer)
}
fun publish(value: T) = consumers.forEach { consumer -> consume.consume(value) }
}

9. Reactive Programming
class Publisher<T> {
private val consumers = mutableListOf<Consumer<T>>()
fun subscribe(consumer: Consumer<T>) {
consumers.add(consumer)
}
fun publish(value: T) = consumers.forEach { consumer -> consumer.consume(value) }
}

10. Reactive Programming
class Publisher<T> {
private val consumers = mutableListOf<Consumer<T>>()
fun subscribe(consumer: Consumer<T>) {
consumers.add(consumer)
}
fun publish(value: T) = consumers.forEach { consumer -> consumer.consume(value) }
}

11. Reactive Programming
class Publisher<T> {
private val consumers = mutableListOf<Consumer<T>>()
fun subscribe(consumer: Consumer<T>) {
consumers.add(consumer)
}
fun publish(value: T) = consumers.forEach { consumer -> consumer.consume(value) }
}

12. Reactive Programming
class CommandExecutor : Consumer<Int> {
override fun consume(command: Int) {
val resp = when (command) {
1 -> "Amaz... zueira é o Mercado Livre HAUAHUHUAAHUA"
2 -> "Figueira né feio"
3 -> throw FinishProgram()
else -> "Essa opção não existe feio"
}
println("Resposta: $resp")
}
}

13. Reactive Programming
class CommandExecutor : Consumer<Int> {
override fun consume(command: Int) {
val resp = when (command) {
1 -> "Amaz... zueira é o Mercado Livre HAUAHUHUAAHUA"
2 -> "Figueira né feio"
3 -> throw FinishProgram()
else -> "Essa opção não existe feio"
}
println("Resposta: $resp")
}
}

14. Reactive Programming
class CommandExecutor : Consumer<Int> {
override fun consume(command: Int) {
val resp = when (command) {
1 -> "Amaz... zueira é o Mercado Livre HAUAHUHUAAHUA"
2 -> "Figueira né feio"
3 -> throw FinishProgram()
else -> "Essa opção não existe feio"
}
println("Resposta: $resp")
}
}

15. Reactive Programming
class CommandExecutor : Consumer<Int> {
override fun consume(command: Int) {
val resp = when (command) {
1 -> "Amaz... zueira é o Mercado Livre HAUAHUHUAAHUA"
2 -> "Figueira né feio"
3 -> throw FinishProgram()
else -> "Essa opção não existe feio"
}
println("Resposta: $resp")
}
}

16. Reactive Programming
class CommandExecutor : Consumer<Int> {
override fun consume(command: Int) {
val resp = when (command) {
1 -> "Amaz... zueira é o Mercado Livre HAUAHUHUAAHUA"
2 -> "Figueira né feio"
3 -> throw FinishProgram()
else -> "Essa opção não existe feio"
}
println("Resposta: $resp")
}
}

17. Reactive Programming
class CommandLogger : Consumer<Int> {
private val logs = mutableListOf<String>()
override fun consume(command: Int) = log(command)
private fun log(command: Int) {
logs.add("[${now()}] command $command")
}
fun printLogs() = logs.forEach(::println)
}

18. Reactive Programming
class CommandLogger : Consumer<Int> {
private val logs = mutableListOf<String>()
override fun consume(command: Int) = log(command)
private fun log(command: Int) {
logs.add("[${now()}] command $command")
}
fun printLogs() = logs.forEach(::println)
}

19. Reactive Programming
class CommandLogger : Consumer<Int> {
private val logs = mutableListOf<String>()
override fun consume(command: Int) = log(command)
private fun log(command: Int) {
logs.add("[${now()}] command $command")
}
fun printLogs() = logs.forEach(::println)
}

20. Reactive Programming
class CommandLogger : Consumer<Int> {
private val logs = mutableListOf<String>()
override fun consume(command: Int) = log(command)
private fun log(command: Int) {
logs.add("[${now()}] command $command")
}
fun printLogs() = logs.forEach(::println)
}

21. Reactive Programming
class CommandLogger : Consumer<Int> {
private val logs = mutableListOf<String>()
override fun consume(command: Int) = log(command)
private fun log(command: Int) {
logs.add("[${now()}] command $command")
}
fun printLogs() = logs.forEach(::println)
}

22. Reactive Programming
class CommandLogger : Consumer<Int> {
private val logs = mutableListOf<String>()
override fun consume(command: Int) = log(command)
private fun log(command: Int) {
logs.add("[${now()}] command $command")
}
fun printLogs() = logs.forEach(::println)
}

23. Reactive Programming
fun main() {
val publisher = Publisher<Int>()
val commandLogger = CommandLogger()
val commandExecutor = CommandExecutor()
publisher.subscribe(commandLogger)
publisher.subscribe(commandExecutor)
try {
val read = Scanner(System.`in`)
while (true) {
menu()
print("Digite a opção desejada: ")
val command = read.nextInt()
publisher.publish(command)
}
} catch (e: FinishProgram) {
println("Comandos executados: ")
commandLogger.printLogs()
print("Encerrando o programa!")
}
}

24. Reactive Programming
fun main() {
val publisher = Publisher<Int>()
val commandLogger = CommandLogger()
val commandExecutor = CommandExecutor()
publisher.subscribe(commandLogger)
publisher.subscribe(commandExecutor)
try {
val read = Scanner(System.`in`)
while (true) {
menu()
print("Digite a opção desejada: ")
val command = read.nextInt()
publisher.publish(command)
}
} catch (e: FinishProgram) {
println("Comandos executados: ")
commandLogger.printLogs()
print("Encerrando o programa!")
}
}

25. Reactive Programming
fun main() {
val publisher = Publisher<Int>()
val commandLogger = CommandLogger()
val commandExecutor = CommandExecutor()
publisher.subscribe(commandLogger)
publisher.subscribe(commandExecutor)
try {
val read = Scanner(System.`in`)
while (true) {
menu()
print("Digite a opção desejada: ")
val command = read.nextInt()
publisher.publish(command)
}
} catch (e: FinishProgram) {
println("Comandos executados: ")
commandLogger.printLogs()
print("Encerrando o programa!")
}
}

26. Reactive Programming
fun main() {
val publisher = Publisher<Int>()
val commandLogger = CommandLogger()
val commandExecutor = CommandExecutor()
publisher.subscribe(commandLogger)
publisher.subscribe(commandExecutor)
try {
val read = Scanner(System.`in`)
while (true) {
menu()
print("Digite a opção desejada: ")
val command = read.nextInt()
publisher.publish(command)
}
} catch (e: FinishProgram) {
println("Comandos executados: ")
commandLogger.printLogs()
print("Encerrando o programa!")
}
}

27. Reactive Programming
fun main() {
val publisher = Publisher<Int>()
val commandLogger = CommandLogger()
val commandExecutor = CommandExecutor()
publisher.subscribe(commandLogger)
publisher.subscribe(commandExecutor)
try {
val read = Scanner(System.`in`)
while (true) {
menu()
print("Digite a opção desejada: ")
val command = read.nextInt()
publisher.publish(command)
}
} catch (e: FinishProgram) {
println("Comandos executados: ")
commandLogger.printLogs()
print("Encerrando o programa!")
}
}

28. Reactive Programming
fun main() {
val publisher = Publisher<Int>()
val commandLogger = CommandLogger()
val commandExecutor = CommandExecutor()
publisher.subscribe(commandLogger)
publisher.subscribe(commandExecutor)
try {
val read = Scanner(System.`in`)
while (true) {
menu()
print("Digite a opção desejada: ")
val command = read.nextInt()
publisher.publish(command)
}
} catch (e: FinishProgram) {
println("Comandos executados: ")
commandLogger.printLogs()
print("Encerrando o programa!")
}
}

29. Reactive Programming
fun main() {
val publisher = Publisher<Int>()
val commandLogger = CommandLogger()
val commandExecutor = CommandExecutor()
publisher.subscribe(commandLogger)
publisher.subscribe(commandExecutor)
try {
val read = Scanner(System.`in`)
while (true) {
menu()
print("Digite a opção desejada: ")
val command = read.nextInt()
publisher.publish(command)
}
} catch (e: FinishProgram) {
println("Comandos executados: ")
commandLogger.printLogs()
print("Encerrando o programa!")
}
}

30. Reactive Programming
fun main() {
val publisher = Publisher<Int>()
val commandLogger = CommandLogger()
val commandExecutor = CommandExecutor()
publisher.subscribe(commandLogger)
publisher.subscribe(commandExecutor)
try {
val read = Scanner(System.`in`)
while (true) {
menu()
print("Digite a opção desejada: ")
val command = read.nextInt()
publisher.publish(command)
}
} catch (e: FinishProgram) {
println("Comandos executados: ")
commandLogger.printLogs()
print("Encerrando o programa!")
}
}

31. Reactive Programming
Reagimos aos comandos publicados!

32. Reactive Programming
Zero acoplamento entre diferentes consumers!

33. Reactive Stream
É uma especificação!

34. ● O que quer dizer especificação?
● Para o que serve essa especificação?
Reactive Stream

35. Reactive Stream
Reactive Stream

36. Reactive Stream
Reactive Stream

37. Reactive Stream
Reactive Stream

38. Reactive Stream
Reactive Stream

39. Reactive Stream
Reactive Stream

40. Reactor
Publishers

41. Reactor
● Mono 0..1
0..infinito● Flux

42. Reactor
Exemplos

43. Reactor
val publisher = Flux.fromArray(arrayOf("Goku", ">", "Naruto"))
publisher.subscribe { value -> print(value) /* consumer */ }
// Imprime: Goku>Naruto

44. Reactor
val publisher = Flux.fromArray(arrayOf("Goku", ">", "Naruto"))
publisher.subscribe { value -> print(value) /* consumer */ }
// Imprime: Goku>Naruto

45. Reactor
val publisher = Flux.fromArray(arrayOf("Goku", ">", "Naruto"))
publisher.subscribe { value -> print(value) /* consumer */ }
// Imprime: Goku>Naruto

46. Reactor
val publisher = Flux.fromArray(arrayOf("Goku", ">", "Naruto"))
publisher.subscribe { value -> print(value) /* consumer */ }
// Imprime: Goku>Naruto

47. Reactor
val publisher = Flux.fromArray(arrayOf("Goku", ">", "Naruto"))
publisher.map(String::toUpperCase)
.map { value -> if(value == ">") "<" else value }
.subscribe { value -> print(value) /* consumer */ }
// Imprime: GOKU<NARUTO

48. Reactor
val publisher = Flux.fromArray(arrayOf("Goku", ">", "Naruto"))
publisher.map(String::toUpperCase)
.map { value -> if(value == ">") "<" else value }
.subscribe { value -> print(value) /* consumer */ }
// Imprime: GOKU<NARUTO

49. Reactor
val publisher = Flux.fromArray(arrayOf("Goku", ">", "Naruto"))
publisher.map(String::toUpperCase)
.map { value -> if(value == ">") "<" else value }
.subscribe { value -> print(value) /* consumer */ }
// Imprime: GOKU<NARUTO

50. Reactor
val publisher = Flux.fromArray(arrayOf("Goku", ">", "Naruto"))
publisher.map(String::toUpperCase)
.map { value -> if(value == ">") "<" else value }
.subscribe { value -> print(value) /* consumer */ }
// Imprime: GOKU<NARUTO

51. Reactor
val publisher = Flux.fromArray(arrayOf("Goku", ">", "Naruto"))
publisher.map(String::toUpperCase)
.map { value -> if(value == ">") "<" else value }
.subscribe { value -> print(value) /* consumer */ }
// Imprime: GOKU<NARUTO

52. Reactor
val publisher = Flux.fromArray(arrayOf("Goku", ">", "Naruto"))
publisher.map(String::toUpperCase)
.map { value -> if(value == ">") "<" else value }
.subscribe { value -> print(value) /* consumer */ }
// Imprime: GOKU<NARUTO

53. Reactor
val monoPublisher = Mono.just("Goku is the best!")
monoPublisher.subscribeOn(Schedulers.parallel())
.subscribe { print("[${Thread.currentThread().name}] $it") }
println("[${Thread.currentThread().name}] Who is the best?")
// Imprime: [main] Who is the best?
// [parallel-1] Goku is the best!

54. Reactor
val monoPublisher = Mono.just("Goku is the best!")
monoPublisher.subscribeOn(Schedulers.parallel())
.subscribe { print("[${Thread.currentThread().name}] $it") }
println("[${Thread.currentThread().name}] Who is the best?")
// Imprime: [main] Who is the best?
// [parallel-1] Goku is the best!

55. Reactor
val monoPublisher = Mono.just("Goku is the best!")
monoPublisher.subscribeOn(Schedulers.parallel())
.subscribe { print("[${Thread.currentThread().name}] $it") }
println("[${Thread.currentThread().name}] Who is the best?")
// Imprime: [main] Who is the best?
// [parallel-1] Goku is the best!

56. Reactor
val monoPublisher = Mono.just("Goku is the best!")
monoPublisher.subscribeOn(Schedulers.parallel())
.subscribe { print("[${Thread.currentThread().name}] $it") }
println("[${Thread.currentThread().name}] Who is the best?")
// Imprime: [main] Who is the best?
// [parallel-1] Goku is the best!

57. Reactor
val monoPublisher = Mono.just("Goku is the best!")
monoPublisher.subscribeOn(Schedulers.parallel())
.subscribe { print("[${Thread.currentThread().name}] $it") }
println("[${Thread.currentThread().name}] Who is the best?")
// Imprime: [main] Who is the best?
// [parallel-1] Goku is the best!

58. Reactor
val monoPublisher = Mono.just("Goku is the best!")
monoPublisher.subscribeOn(Schedulers.parallel())
.subscribe { print("[${Thread.currentThread().name}] $it") }
println("[${Thread.currentThread().name}] Who is the best?")
// Imprime: [main] Who is the best?
// [parallel-1] Goku is the best!

59. Arquitetura do Webflux
@Controller, @RequestMapping Router functions
spring-webflux
HTTP / Reactive Streams
Tomcat, Jetty, Netty,
Undertow
spring-webmvc
Servlet API
Servlet Container

60. Webflux
Talk is cheap, show me the code!

61. Blocking IO
Thread
Waiting
Running

62. Blocking IO
Thread
Waiting
Running

63. Blocking IO
Thread
Waiting
Running
Chamada ao
database

64. Blocking IO
IO Operation
Thread
Waiting
Running
Chamada ao
database

65. Blocking IO
IO Operation
Thread
Waiting
Running
Resposta do
database

66. Blocking IO
IO Operation
Thread
Waiting
Running
Resposta do
database

67. Non-blocking IO
Thread
Running
Kernel Process

68. Non-blocking IO
Thread
Running
Kernel Process

69. Non-blocking IO
Thread
Running
Kernel Process Chamada ao
database

70. Non-blocking IO
IO Operation
Thread
Running
Kernel Process
Thread sendo
aproveitada para
outros processos

71. Non-blocking IO
IO Operation
Thread
Running
Kernel Process Resposta do
database

72. Non-blocking IO
IO Operation
Thread
Running
Kernel Process

73. Event loop
É um design pattern!

74. Event loop
Event Queue

75. Event loop
Event Queue

76. Event loop
Event Loop
Thread
Event Queue

77. Event loop
Event Loop
Thread
Event Queue

78. Event loop
Event Loop
Thread
Event Queue

79. Event loop
class EventLoop(private val eventQueue: BlockingQueue<Runnable>) {
init {
start()
}
private fun start() {
Thread(Runnable {
var task = eventQueue.take()
while (true) {
task.run()
task = eventQueue.take()
}
}).start()
}
fun put(task: Runnable) {
eventQueue.put(task)
}
}

80. Event loop
class EventLoop(private val eventQueue: BlockingQueue<Runnable>) {
init {
start()
}
private fun start() {
Thread(Runnable {
var task = eventQueue.take()
while (true) {
task.run()
task = eventQueue.take()
}
}).start()
}
fun put(task: Runnable) {
eventQueue.put(task)
}
}

81. Event loop
class EventLoop(private val eventQueue: BlockingQueue<Runnable>) {
init {
start()
}
private fun start() {
Thread(Runnable {
var task = eventQueue.take()
while (true) {
task.run()
task = eventQueue.take()
}
}).start()
}
fun put(task: Runnable) {
eventQueue.put(task)
}
}

82. Event loop
class EventLoop(private val eventQueue: BlockingQueue<Runnable>) {
init {
start()
}
private fun start() {
Thread(Runnable {
var task = eventQueue.take()
while (true) {
task.run()
task = eventQueue.take()
}
}).start()
}
fun put(task: Runnable) {
eventQueue.put(task)
}
}

83. Event loop
class EventLoop(private val eventQueue: BlockingQueue<Runnable>) {
init {
start()
}
private fun start() {
Thread(Runnable {
var task = eventQueue.take()
while (true) {
task.run()
task = eventQueue.take()
}
}).start()
}
fun put(task: Runnable) {
eventQueue.put(task)
}
}

84. Event loop
class EventLoop(private val eventQueue: BlockingQueue<Runnable>) {
init {
start()
}
private fun start() {
Thread(Runnable {
var task = eventQueue.take()
while (true) {
task.run()
task = eventQueue.take()
}
}).start()
}
fun put(task: Runnable) {
eventQueue.put(task)
}
}

85. Event loop
class EventLoop(private val eventQueue: BlockingQueue<Runnable>) {
init {
start()
}
private fun start() {
Thread(Runnable {
var task = eventQueue.take()
while (true) {
task.run()
task = eventQueue.take()
}
}).start()
}
fun put(task: Runnable) {
eventQueue.put(task)
}
}

86. Event loop
class EventLoop(private val eventQueue: BlockingQueue<Runnable>) {
init {
start()
}
private fun start() {
Thread(Runnable {
var task = eventQueue.take()
while (true) {
task.run()
task = eventQueue.take()
}
}).start()
}
fun put(task: Runnable) {
eventQueue.put(task)
}
}

87. Event loop
class EventLoop(private val eventQueue: BlockingQueue<Runnable>) {
init {
start()
}
private fun start() {
Thread(Runnable {
var task = eventQueue.take()
while (true) {
task.run()
task = eventQueue.take()
}
}).start()
}
fun put(task: Runnable) {
eventQueue.put(task)
}
}

88. Event loop
class EventLoop(private val eventQueue: BlockingQueue<Runnable>) {
init {
start()
}
private fun start() {
Thread(Runnable {
var task = eventQueue.take()
while (true) {
task.run()
task = eventQueue.take()
}
}).start()
}
fun put(task: Runnable) {
eventQueue.put(task)
}
}

89. Event loop
E se for necessário conectar com o DB ou ler um
arquivo, isso não vai bloquear o Event Loop?

90. Event loop
Event Loop
Kernel
Thread
Event Queue

91. Event loop
Event Loop
Non-blocking
ops
Kernel
Thread
Event Queue

92. Event loop
Event Loop
Non-blocking
ops
Kernel
Thread
Event Queue
put(event)

93. Event loop - NIO Libs
● R2DBC - Reactive Relational Database Connectivity
● Web Client
● Reactor Netty (UDP, TCP, HTTP)

94. Event loop
E se caso essa rotina for estritamente
bloqueante? Por exemplo, uma que use muito
CPU Bound. O que deve ser feito?

95. Event loop
Event Loop
Worker
Thread Pool
Event Queue
Thread

96. Event loop
Event Loop
Blocking Ops
Worker
Thread Pool
Event Queue
Thread

97. Event loop
Event Loop
Blocking Ops
Worker
Thread Pool
Event Queue
Thread
put(event)

98. Event Loop - CPU Bound exemplo
fun doHeavyProcess() {
println("running other spring boot application rs")
}

99. Event Loop - CPU Bound exemplo
@PostMapping("/heavy-process")
fun heavyProcess(): Mono<ResponseEntity<Nothing>> {
return Mono
.defer { Mono.justOrEmpty(::doHeavyProcess) }
.subscribeOn(Schedulers.parallel())
.map { ResponseEntity.ok().build<Nothing>() }
}

100. Event Loop - CPU Bound exemplo
@PostMapping("/heavy-process")
fun heavyProcess(): Mono<ResponseEntity<Nothing>> {
return Mono
.defer { Mono.justOrEmpty(::doHeavyProcess) }
.subscribeOn(Schedulers.parallel())
.map { ResponseEntity.ok().build<Nothing>() }
}

101. Event Loop - CPU Bound exemplo
@PostMapping("/heavy-process")
fun heavyProcess(): Mono<ResponseEntity<Nothing>> {
return Mono
.defer { Mono.justOrEmpty(::doHeavyProcess) }
.subscribeOn(Schedulers.parallel())
.map { ResponseEntity.ok().build<Nothing>() }
}

102. Event Loop - CPU Bound exemplo
@PostMapping("/heavy-process")
fun heavyProcess(): Mono<ResponseEntity<Nothing>> {
return Mono
.defer { Mono.justOrEmpty(::doHeavyProcess) }
.subscribeOn(Schedulers.parallel())
.map { ResponseEntity.ok().build<Nothing>() }
}

103. Vantagens e Desvantagens
Disclaimer

104. + Utiliza melhor os recursos do hardware
+ Alta disponibilidade
Vantagens

105. - Codebase mais complexo
- É mais complexo para debugar
- Suposições erradas podem bloquear todo o servidor
- Não trabalha com thread local
- Logs
- Telemetria
- Stack Traces podem se tornar inúteis
Desvantagens

106. Referências
● https://medium.com/@rarepopa_68087/reactive-programming-with-spring-boot-and-webflux-734086f8c8a5
● https://tanzu.vmware.com/content/slides/reactive-applications-on-apache-tomcat-and-servlet-3-1-containers
● https://blog.codecentric.de/en/2019/04/explain-non-blocking-i-o-like-im-five/
● https://www.youtube.com/watch?v=2oXqbLhMS_A
● https://medium.com/ing-blog/how-does-non-blocking-io-work-under-the-hood-6299d2953c74
● https://www.scnsoft.com/blog/java-reactive-programming
● https://www.slideshare.net/kslisenko/networking-in-java-with-nio-and-netty-76583794
● https://www.reactivemanifesto.org/glossary#Non-Blocking
● https://docs.spring.io/spring-framework/docs/current/spring-framework-reference/web-reactive.html
● https://dzone.com/articles/spring-webflux-eventloop-vs-thread-per-request-mod
● https://www.reactive-streams.org/
● https://projectreactor.io/docs/core/release/reference/
● http://tutorials.jenkov.com/netty/overview.html

107. Códigos de exemplo
https://github.com/wellington3110/webfluxpresentation

108. !!!
/wellington3110
/in/wgmacedo/
wellingtongustavomacedo@gmail.com
Wellington Gustavo Macedo