Reactive Programming with RxJava

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Reactive Programming with RxJava Catalog Tribe in Shanghai [email protected] 2018.01.18 1

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Agenda • Why Reactive Programming? • RxJava Observable • RxJava Operators • RxJava Schedulers • References 2

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Why Reactive

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High available system Service Infinite streams Many slow connections Depends A Depends B Slow remote services

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Blocking vs Non-Blocking

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ReactiveX • Started by Microsoft Rx Lib (Reactive Extensions) • For composing asynchronous and event-based programs by using observable sequences • Easy way to implement complicated non-blocking system • Easy to combine multiple data source responses • Resiliency / Fault tolerance / Deal heavy load • Why Reactive

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Reactive Streams Publisher Subscriber

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Reactive Streams Publisher Subscriber

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Reactive Streams Publisher Subscriber Subscribe then request data (Backpressure)

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Reactive Streams Publisher Subscriber Subscribe then request data (Backpressure)

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Reactive Streams Publisher Subscriber Subscribe then request data (Backpressure)

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Reactive Streams Publisher Subscriber Subscribe then request data (Backpressure) 0..N Data published then 0..1 (Error or Completed)

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Reactive Streams Publisher Subscriber Subscribe then request data (Backpressure) 0..N Data published then 0..1 (Error or Completed) Example : Using Message Queue 1. Polling message queue for new message (traditional Kafka client) 2. Listener or callback for new message (spring-kafka use listener) 3. Reactive stream (kakfa streams) is reactive streams

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Observable RxJava

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Iterable vs Observable Event Iterable (pull) Observable (push) Receive data T next() onNext(T) Discover error Throw Exception onError(Exception) Complete !hasNext() onCompleted()

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Use Observable getDataFromLocalMemory() .skip(10) .take(5) .map { s -> s + " transformed" } .forEach { println(“next => " + it) } Iterable Observable getDataFromNetwork() .skip(10) .take(5) .map { s -> s + " transformed" } .subscribe { println(“next => " + it) }

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Why Use Observable • Observables are composable • Observables are Flexible • Observables are less opinionated • Various implementation (thread-pool, event loops, non- blocking I/O) • Callback is hard to implement and maintain • Not only for UI, Useful for Distributed System

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Structure of Observable

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Cold vs Hot Observable • Cold Observable • Like VOD (Video on demand) (Finite stream) • At time to subscribe, you can receive first data • Other subscribe, receive first data also • Hot Observable • Like TV or Radio (Infinite Stream) • At time to subscribe, you can receive published data at that time

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Other Objects • Flowable (RxJava2) • Observable with back pressure • Single • onSuccess/onFailure • Completable • onCompleted with no returns • Maybe (RxJava2) • Single + Completable

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Subject • Observable + Observer • Varieties of Subject • AsyncSubject - take last elements • BehaviorSubject - like hot observable + latest element • PublishSubject - like hot observable • ReplaySubject - cold observable

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Operators RxJava

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Operators example

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Operators example fun fetchWeather(city:String):Single

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Operators example fun fetchWeather(city:String):Single

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Operators example fun fetchWeather(city:String):Single

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Operators example

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Operators example

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Operators example

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Operators example

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Operators example Times out and emits an error after 2 sec

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Operators example Times out and emits an error after 2 sec

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Operators example

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Operators example

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Operators example Logs a message in case of error

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Operators example Logs a message in case of error

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Operators example

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Operators example

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Operators example Switches to a different service in case of error

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Operators example Switches to a different service in case of error

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Operators example

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Operators example

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Operators example Transform a weather instance into a string message

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Operators example Transform a weather instance into a string message

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Operators example

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Operators example

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Operators example Triggers the processing of the chain

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Marble Diagram - zip

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Marble Diagram - zip UpStream

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Marble Diagram - zip UpStream Operator

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Marble Diagram - zip UpStream DownStream Operator

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Marble Diagram - flatMap

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