Hands-on Lab: Making the paradigm-shift to Reactive Programming with Spring 5 Web Reactive @ J-Fall16

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Let’s do this before we start git clone https://bitbucket.org/rlippolis/spring-web-reactive-workshop mememon-go-client -> npm install mememon-go-server -> mvn clean verify reactive-spring-intro -> mvn clean verify npm install -g angular-cli

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Reactive Programming with Spring 5 Web Reactive Riccardo Lippolis - JDriven Bas W. Knopper - JCore

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Who are we?

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● Presentation ○ Intro ○ Quick dive into Reactive Programming ○ Reactive Streams Specification ○ Reactor ○ Spring Web Reactive ○ Examples Agenda

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Quick Dive into Reactive Programming

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Increase in User Expectance Applications used to have •Couple of servers •Seconds of response time •Hours of offline maintenance •Gigabytes of data to process Today, users expect •Desktop, web & mobile support •Milliseconds response time •100% uptime •Petabytes of data to process

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Reactive System

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Reactive Programming • Extending the observer pattern • Abstract away concerns • Low-level threading, Synchronization, Thread-safety, Concurrent data structures, Non-blocking I/O • Observable model • Streams of asynchronous events • Composable operations • No more callback hell!

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Manipulating data

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Java 8 Streams vs. Reactive Streams • A Stream is pull-based • it "asks" for items to process. • Reactive Streams are push-based • you are notified when an element is available.

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Backpressure what if you can’t handle the data?

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Frameworks? Libraries?

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Reactive Extensions

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Reactive Streams

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Reactive Streams • A standard for asynchronous stream processing with non-blocking backpressure • Inspired by Reactive Extensions API • The API consists of the following components that are required to be provided by Reactive Stream implementations • Publisher • Subscriber • Subscription • Processor

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“That’s it? I can implement that!” - Random developer “Just don’t...” - Bas & Riccardo

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Reactor projectreactor.io

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Reactor • Made by Pivotal! (Spring FTW \0/) • A foundation for asynchronous applications on the JVM • Interact directly with • Java 8 functional API • CompletableFuture • Stream • Duration • Based on the Reactive Streams Specification (same concepts, different naming) • Latest: 3.0.2.RELEASE

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Flux and Mono

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Flux and Mono

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Examples - Creating Reactive Streams • Arbitrary number of items: Flux flux = Flux. just("Hello", "World!"); • Converting an existing collection / Java 8 Stream: List list = Arrays. asList(1, 3, 5); Flux flux = Flux. fromIterable(list); Flux flux = Flux. fromStream(list.stream()); • Empty stream: Flux.empty();

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Examples - Manipulating Streams • Filtering Flux.just(1, 2, 3, 4, 5).filter(n -> n % 2 == 0); // [2, 4] • Transforming Flux.just(1, 2, 3, 4, 5).map(i -> i * 2); // [2, 4, 6, 8, 10] • Distinct only Flux.just("a", "a", "b", "c").distinct(); // [a, b, c]

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Examples - Consuming Streams Flux.just("Hello", " ", "World!").subscribe(System. out::print); // Hello World!

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Examples - Consuming Streams With a custom Subscriber Flux.just("Hello", " ", "World!").subscribe( new Subscriber() { @Override public void onSubscribe(Subscription s) { s.request(Long. MAX_VALUE); } @Override public void onNext(String s) { System. out.println("Received: " + s); } @Override public void onError(Throwable t) { System. err.println("Error: " + t.toString()); } @Override public void onComplete() { System. out.println("Done!"); } });

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Spring Web Reactive

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Spring Web Reactive Uses the familiar Spring MVC programming model (@Controller, etc.)... ...but with a new reactive, non-blocking engine

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Traditional Servlet Engine vs Reactive Engine Traditional

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Traditional Servlet Engine vs Reactive Engine Traditional Reactive

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Implementation • Implemented using Project Reactor • Uses Flux (0..N) and Mono (0..1) • Compatible with RxJava • Return Observables from your REST controllers

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Current state of implementation • Version: 5.0 M2 (Not production ready!) • Focus on REST • Basic HTML rendering supported (Freemarker) • Support for • JSON (Jackson) • XML (JAXB) • SSE streaming • Zero-copy file transfers • • Functional Web Framework -> Not today

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Examples - Using Streams • With a Spring @RestController @RestController public class MyController { @GetMapping ("count") public Flux count( @RequestParam ("to") int to) { return Flux.range(1, to); } } GET http://localhost:8080/count?to=5 -> [1, 2, 3, 4, 5]

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Reactive Pitfalls Looks very cool, but… • Declarative style of coding is hard(er) to debug • “When is my code executed? (If ever)” • Appears to be multithreaded by default, but isn’t • Design choice "if there’s no explicit request to switch threads it stays on the same one for the next call, whatever that is"

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Workshop part 1: Master the koans ● Open the reactive-spring-intro project ● Fix all the tests / koans in: src/test/java/com/jdriven/reactive/exercises

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Workshop part 2: Mememon Go ● Demo explaining Use case ● Make all the tests pass by implementing the code ● Make the application work :)

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Coming up • Support for Reactive types in other Spring projects, e.g.: • Spring Data • Spring Cloud • Spring Security • GA Release • Current release: 5.0 M2 • GA not before March 2017

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Great work everybody!