Reaktive Anwendungen mit RxJava. Dr. Michael Menzel

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1 Reaktive Anwendungen mit RxJava Dr. Michael Menzel

2 DIGITALIZATION

3 DIGITALIZATION

4 DIGITALIZATION

5 DIGITALIZATION

6 REACTIVE ARCHITECTURES How can we build highly interactive (responsive) systems, which are able to operate under high load and huge data volume?

7 REACTIVE ARCHITECTURES How much load will the Christmas Season put on my systems? Elasticity transparent scale-out dynamic provisioning of resources

8 REACTIVE ARCHITECTURES A distributed system is one in which the failure of a system you did not even know existed can render your own computer unusable. - Leslie Lamport

9 REACTIVE ARCHITECTURES A distributed system is one in which the failure of a system you did not even know existed can render your own computer unusable. - Leslie Lamport Crash Failure, Omission Failure, Timing Failure, Response Failure, Byzantine Failure Do not try to avoid Failures. Embrace them.

10 REACTIVE ARCHITECTURES Resilience The system stays responsive in the face of failure with a graceful degradation of service if required retry & failover replication isolation & error propagation loose coupling

11 REACTIVE ARCHITECTURES Value Responsiveness Means Elasticity Resilience Implementation Message-driven The Reactive Manifesto,

Universitätsring 8f Search in progress Nobody likes to wait and look at an AJAX loading

12 REACTIVE ARCHITECTURES Schmidt Search Messagedriven Streaming of search results Hans Schmidt Köln, Blumenweg 13 Kurt Schmidt Frankfurt, Weinstock 36 Michael Schmidt Trier, Universitätsring 8f Search in progress Nobody likes to wait and look at an AJAX loading indicator excellent user experience Asynchronous, non-blocking data processing push-based communication

13 REACTIVE ARCHITECTURES RxNetty Non-Blocking API Asynchronicity Event-driven

14 Connection Acceptor Thread Request HandleThread Request HandleThread REACTIVE ARCHITECTURES Servlet Container Backend Thread Pool Blocking Invocation Blocking Invocation Servlet Model: One thread per request Synchronous programming model Blocking Invocations Shared state and locks

Connection Acceptor Thread REACTIVE ARCHITECTURES Event-Driven Application Backend Event Queue Request Handler Request Handler Non-Blocking Invocation Non-Blocking Invocation

15 Connection Acceptor Thread REACTIVE ARCHITECTURES Event-Driven Application Backend Event Queue Request Handler Request Handler Non-Blocking Invocation Non-Blocking Invocation Event-driven application: Single-threaded event loop 1 Asynchronous event handling 2 Callback Handler Callback Handler 1 2 No locks / synchronization required Single Threaded Event Loop

16 REACTIVE ARCHITECTURES Messaging vs Eventing Communication between systems / processes Directed information Supports communication patterns & timeouts Foundation for elasticity, resilience, responsiveness Representation of local facts (that someone can consume) Can be exchanged as messages Processed by short living functional chains Subject of reactive Programming Reactive Programming: Foundation of Reactive Architectures

17 REACTIVE PROGRAMMING single data set multiple data sets synchronous Object Iterable Stream asynchronous Callback Future CompletableFuture Callback, Observable

18 REACTIVE PROGRAMMING Update customer data 1) Find customer by id 2) Change address information 3) Update customer data

REACTIVE PROGRAMMING try { //load customer data Customer customer = customerservice.findbyid (customerid); //update customer address customer.setaddress(.

19 REACTIVE PROGRAMMING try { //load customer data Customer customer = customerservice.findbyid (customerid); //update customer address customer.setaddress(... ); //save customer data customerservice.update(customer); } catch (RuntimeException ex) { //process error } Easy to read and implement Exception-based error handling

20 REACTIVE PROGRAMMING // load customer data vertx.eventbus().send("customerservice.findbyid", customerid, reply -> { } // check on error if (reply.succeeded()) { // extract customer from reply Customer customer = (Customer) reply.result().body(); // update address customer.setaddress( "..." ); // update customer vertx.eventbus().send("customerservice.update", customer, updatereply -> { //... // nested code for error checking and processing //... }); } else { // process error Nested code leads to callback hell

21 REACTIVE PROGRAMMING single data set multiple data sets synchronous Object Iterable Stream asynchronous Callback Future CompletableFuture Callback, Observable

22 RxJava RxJava is a library for composing asynchronous and event-based programs using observable sequences

23 RxJava RxJava is based on the observer pattern Observer subscribe onnext(t) onerror(throwable t) oncompleted() Observable

24 RxJava // asynchronous method returns an observable Observable<Customer> obs = customerservice.findbyname("schmidt"); // subscribe to the event stream obs.subscribe(customer -> System.out.println(customer), error -> System.out.println(error), () -> System.out.println("completed"));

RxJava // asynchronous method returns an observable customerservice.findbyname("schmidt").filter(customer -> customer.getfirstname().equals("hans")).map(customer -> customer.

25 RxJava // asynchronous method returns an observable customerservice.findbyname("schmidt").filter(customer -> customer.getfirstname().equals("hans")).map(customer -> customer.getid()) // subscribe to the event stream.subscribe(customerid -> System.out.println(customerId), error -> System.out.println(error), () -> System.out.println("completed"));

26 RxJava Map ( x => 10 * x)

27 RxJava FlatMap ( )

RxJava // asynchronous send method returns an observable vertx.eventbus().sendobservable("customerservice.findbyid", "123") //extract customer from response.map(asyncresult -> (Customer) asyncresult.

28 RxJava // asynchronous send method returns an observable vertx.eventbus().sendobservable("customerservice.findbyid", "123") //extract customer from response.map(asyncresult -> (Customer) asyncresult.body()) //update customer object.map(customer ->... ) //save customer data.flatmap(customer -> vertx.eventbus().sendobservable("customerservice.update", customer)) //consume result and error.subscribe(customer ->..., error ->... );

29 RxJava Cold Hot Observable vs Observable Observer Observer Observable Observer Observer Observable 1 subscribe subscribe subscribe subscribe 3

30 RxJava LINQ,.NET Framework 3.5 Language extension to query and transform data RxJS Rx for JavaScript Reactive Streams Specification and Java 9 Flow API Rx.NET,.NET Framework 4 Rx = Observables + LINQ + Schedulers Asynchronous, Push based data processing RxJava Reactive Extensions for the JVM, started by Netflix RxJava 2.0 Redesign based on Reactive Streams

31 RxJava Event-Driven Application Observable Event Queue Request Handler Event Handler Event Handler subscribe n What if the Supplier of events is faster than the Consumer? Back-Pressure required Single Threaded Event Loop

32 RxJava Event-Driven Application Observable Back-Pressure Event Queue Single Threaded Event Loop Request Handler Subscribe (2) Event Handler Event Handler 2 Request (1) 3 Request (1) 4 Reactive pull Avoid event buffering Limited to specific use cases (cold observables) RxJava: - Base class Observable: No Backpressure - Base class Flow: Reactive Stream implementation with Backpressure

33 REACTIVE FRAMEWORKS Reactive Library Preferred Platform RxJava RxNetty Reactor akka Streams

34 GATEWAY SERVICES WITH RXJAVA Browser Gateway Service Gateway Service Customer Service Account Service PUSH Gateway Service Gateway Service Transaction Service Legacy User Service Clients Services

35 RxJava Asynchronous / parallel / non-blocking Fluent API/ combination of asynchronous calls Observable creation, data transformation, filtering and error handling Stream support: foundation for server to client push and provision of partial results

36 Reaktive Anwendungen mit RxJava Dr. Michael Menzel

Writing Reactive Application using Angular/RxJS, Spring WebFlux and Couchbase. Naresh Chintalcheru

Writing Reactive Application using Angular/RxJS, Spring WebFlux and Couchbase Naresh Chintalcheru Who is Naresh Technology professional for 18+ years Currently, Technical Architect at Cars.com Lecturer