Futures and Rx Observables: powerful abstractions for consuming web services asynchronously (#springone #s2gx)

@crichardson
Consuming web services asynchronously
with Futures
and Rx Observables
Chris Richardson
Author of POJOs in Action
Founder of the original CloudFoundry.com
@crichardson
chris@chrisrichardson.net
http://plainoldobjects.com

@crichardson
Presentation goal
Learn how to use (Scala) Futures
and Rx Observables to write
simple yet robust and scalable
concurrent code

@crichardson
About Chris
http://www.theregister.co.uk/2009/08/19/springsource_cloud_foundry/

@crichardson
Agenda
The need for concurrency
Simplifying concurrent code with Futures
Taming callback hell with JavaScript promises
Consuming asynchronous streams with Reactive Extensions

@crichardson
Let’s imagine you are building an online
store

@crichardson
Shipping
Recomendations
Product
Info
Reviews

@crichardson
Reviews
Product
Info
Sales
ranking

@crichardson
Related
books
Viewing
history
Forum

@crichardson
Application architecture
Product Info Service
Desktop
browser
Native mobile
client
REST
REST
REST
Recomendation Service
Review Service
Front end server
API gatewayREST
Mobile
browser
Web Application
HTML

@crichardson
Handling getProductDetails()
Front-end server
Recommendations
Service
Review
Service
getProductInfo()
getRecommendations()
getReviews()
getProductDetails()

@crichardson
Handling getProductDetails() - sequentially
Front-end server
Recommendations
Service
Review
Service
getProductInfo()
getReviews()
getProductDetails()
Higher response time :-(

@crichardson
Handling getProductDetails() - in parallel
Front-end server
Recommendations
Service
Review
Service
getProductInfo()
getReviews()
getProductDetails()
Lower response time :-)

@crichardson
Implementing a concurrent REST client
Thread-pool based approach
executorService.submit(new Callable(...))
Simpler but less scalable - lots of idle threads consuming memory
Event-driven approach
NIO with completion callbacks
More complex but more scalable

@crichardson
The front-end server must handle partial
failure of backend services
Front-end server
Recommendations
Service
Review
Service
getProductInfo()
getReviews()
getProductDetails()
X
How to provide a
good user
experience?

@crichardson
Futures are a great concurrency
abstraction
http://en.wikipedia.org/wiki/Futures_and_promises

@crichardson
How futures work
Outcome
Future
Client
get
Asynchronous
operation
set
initiates

@crichardson
Beneﬁts
Client does not know how the asynchronous operation is implemented
Client can invoke multiple asynchronous operations and gets a Future for each
one.

@crichardson
REST client using Spring @Async
@Component
class ProductInfoServiceImpl extends ProducInfoService {
val restTemplate : RestTemplate = ...
@Async
def getProductInfo(productId: Long) = {
new AsyncResult(restTemplate.getForObject(....)...)
}
}
Execute asynchronously in thread pool
A Future
containing a value
trait ProductInfoService {
def getProductInfo(productId: Long): java.util.concurrent.Future[ProductInfo]
}

@crichardson
ProductDetailsService
@Component
class ProductDetailsService
@Autowired()(productInfoService: ProductInfoService,
reviewService: ReviewService,
recommendationService: RecommendationService) {
def getProductDetails(productId: Long): ProductDetails = {
val productInfoFuture = productInfoService.getProductInfo(productId)
}
}
val recommendationsFuture = recommendationService.getRecommendations(productId)
val reviewsFuture = reviewService.getReviews(productId)
val productInfo = productInfoFuture.get(300, TimeUnit.MILLISECONDS)
val recommendations =
recommendationsFuture.get(10, TimeUnit.MILLISECONDS)
val reviews = reviewsFuture.get(10, TimeUnit.MILLISECONDS)
ProductDetails(productInfo, recommendations, reviews)

@crichardson
ProductController
@Controller
class ProductController
@Autowired()(productDetailsService : ProductDetailsService) {
@RequestMapping(Array("/productdetails/{productId}"))
@ResponseBody
def productDetails(@PathVariable productId: Long) =
productDetailsService.getProductDetails(productId)

@crichardson
Not bad but...
val productInfo =
productInfoFuture.get(300, TimeUnit.MILLISECONDS)
Blocks Tomcat thread until Future
completes
Not so scalable :-(

@crichardson
... and also...
Java Futures work well for a single-level of asynchronous execution
BUT
#fail for more complex, scalable scenarios
Difficult to compose and coordinate multiple concurrent operations
http://techblog.netflix.com/2013/02/rxjava-netflix-api.html

@crichardson
Better: Futures with callbacks no blocking!
val f : Future[Int] = Future { ... }
f onSuccess {
case x : Int => println(x)
}
f onFailure {
case e : Exception => println("exception thrown")
}
Guava ListenableFutures, Spring 4 ListenableFuture
Java 8 CompletableFuture, Scala Futures

@crichardson
Even better: Composable Futures
val f1 = Future { ... ; 1 }
val f2 = Future { ... ; 2 }
val f4 = f2.map(_ * 2)
assertEquals(4, Await.result(f4, 1 second))
val fzip = f1 zip f2
assertEquals((1, 2), Await.result(fzip, 1 second))
Transforms Future
Combines two futures
Scala, Java 8 CompletableFuture (partially)

@crichardson
Scala futures are Monads
def callB() : Future[...] = ...
def callC() : Future[...] = ...
def callD() : Future[...] = ...
val result = for {
(b, c) <- callB() zip callC();
d <- callD(b, c)
} yield d
result onSuccess { .... }
Two calls execute in parallel
And then invokes D
Get the result of D

@crichardson
Scala Future + RestTemplate
import scala.concurrent.Future
@Component
class ProductInfoService {
def getProductInfo(productId: Long): Future[ProductInfo] = {
Future { restTemplate.getForObject(....) }
}
}
Executes in thread pool
Scala Future

@crichardson
Scala Future + RestTemplate
class ProductDetailsService @Autowired()(....) {
def getProductDetails(productId: Long) = {
val productInfoFuture = productInfoService.getProductInfo(productId)
val recommendationsFuture = recommendationService.getRecommendations(productId)
val reviewsFuture = reviewService.getReviews(productId)
for (((productInfo, recommendations), reviews) <-
productInfoFuture zip recommendationsFuture zip reviewsFuture)
yield ProductDetails(productInfo, recommendations, reviews)
}
}
Non-blocking!

@crichardson
Async Spring MVC + Scala Futures
@Controller
class ProductController ... {
@ResponseBody
def productDetails(@PathVariable productId: Long) = {
val productDetails =
productDetailsService.getProductDetails(productId)
val result = new DeferredResult[ProductDetails]
productDetails onSuccess {
case r => result.setResult(r)
}
productDetails onFailure {
case t => result.setErrorResult(t)
}
result
}
Convert Scala Future to
Spring MVC
DeferredResult

@crichardson
Servlet layer is asynchronous but the
backend uses thread pools
Need event-driven REST client

@crichardson
About the Reactor pattern
Deﬁned by Doug Schmidt in 1995
Pattern for writing scalable servers
Alternative to thread-per-connection model
Single threaded event loop dispatches events on handles (e.g. sockets, ﬁle
descriptors) to event handlers

@crichardson
Reactor pattern structure
Event Handler
handle_event(type)
get_handle()
Initiation Dispatcher
handle_events()
register_handler(h)
select(handlers)
for each h in handlers
h.handle_event(type)
end loop
handle
Synchronous Event
Demultiplexer
select()
owns
notiﬁes
uses
handlers
Application
creates

@crichardson
Java NIO Selectors = Reactor pattern
But that’s super low-level :-(

@crichardson
New in Spring 4
Mirrors RestTemplate
Methods return a ListenableFuture = JDK 7 Future + callback methods
Can use HttpComponents NIO-based AsyncHttpClient
Spring AsyncRestTemplate

@crichardson
Using the AsyncRestTemplate
http://hc.apache.org/httpcomponents-asyncclient-dev/
val asyncRestTemplate = new AsyncRestTemplate(
new HttpComponentsAsyncClientHttpRequestFactory())
override def getProductInfo(productId: Long) = {
val listenableFuture =
asyncRestTemplate.getForEntity("{baseUrl}/productinfo/{productId}",
classOf[ProductInfo],
baseUrl, productId)
toScalaFuture(listenableFuture).map { _.getBody }
}
Convert to Scala Future and get entity

@crichardson
Converting ListenableFuture to Scala Future
implicit def toScalaFuture[T](f : ListenableFuture[T]) : Future[T] = {
val p = promise[T]
f.addCallback(new ListenableFutureCallback[T] {
def onSuccess(result: T) { p.success(result)}
def onFailure(t: Throwable) { p.failure(t) }
})
p.future
}
The producer side of Scala Futures
Supply outcome
Return future

@crichardson
Now everything is non-blocking :-)

@crichardson
If recommendation service is down...
Never responds front-end server waits indeﬁnitely
Consumes valuable front-end server resources
Page never displayed and customer gives up
Returns an error
Error returned to the front-end server error page is displayed
Customer gives up

@crichardson
Fault tolerance at Netflix
Network timeouts and retries
Invoke remote services via a bounded thread pool
Use the Circuit Breaker pattern
On failure:
return default/cached data
return error to caller
Implementation: https://github.com/Netflix/Hystrix
http://techblog.netflix.com/2012/02/fault-tolerance-in-high-volume.html

@crichardson
Using Hystrix
@Component
class ProductInfoServiceImpl extends ProductInfoService {
val restTemplate = RestTemplateFactory.makeRestTemplate()
val baseUrl = ...
class GetProductInfoCommand(productId: Long)extends
HystrixCommand[ProductInfo](....) {
override def run() =
restTemplate.
getForEntity("{baseUrl}/productinfo/{productId}",
classOf[ProductInfo],
baseUrl, productId).getBody
}
def getProductInfoUsingHystrix(productId: Long) : Future[ProductInfo] = {
new GetProductInfoCommand(productId).queue()
}
}
Runs in thread pool
Returns JDK Future

@crichardson
But how to accomplish this with event-
driven code

@crichardson
How to handling partial failures?
productDetailsFuture zip
recommendationsFuture zip reviewsFuture
Fails if any Future has failed

@crichardson
Handling partial failures
val recommendationsFuture =
recommendationService.
getRecommendations(userId,productId).
recover {
case _ => Recommendations(List())
}
“catch-like” Maps Throwable to value

@crichardson
Implementing a Timeout
resultFuture onSuccess { case r => result.setResult(r) }
resultFuture onFailure { case t => result.setErrorResult(t) }
No timeout - callbacks might never be
invoked :-(
Await.result(resultFuture, timeout)
Blocks until timeout:-(

@crichardson
Non-blocking Timeout
http://eng.42go.com/future-safefuture-timeout-cancelable/
object TimeoutFuture {
def apply[T](future: Future[T], onTimeout: => Unit = Unit)
(implicit ec: ExecutionContext, after: Duration): Future[T] = {
val timer = new HashedWheelTimer(10, TimeUnit.MILLISECONDS)
val promise = Promise[T]()
val timeout = timer.newTimeout(new TimerTask {
def run(timeout: Timeout){
onTimeout
promise.failure(new TimeoutException(s"Future timed out after ${after.toMillis}ms"))
}
}, after.toNanos, TimeUnit.NANOSECONDS)
Future.firstCompletedOf(Seq(future, promise.future)).
tap(_.onComplete { case result => timeout.cancel() })
}
}
val future = ...
val timedoutFuture = TimeoutFuture(future)(executionContext, 200.milleseconds)
Timer fails
promise
Outcome of ﬁrst
completed

@crichardson
Using the Akka Circuit Breaker
import akka.pattern.CircuitBreaker
val breaker =
new CircuitBreaker(actorSystem.scheduler,
maxFailures = 1,
callTimeout = 100.milliseconds,
resetTimeout = 1.minute)
val resultFuture = breaker.
withCircuitBreaker{ asynchronousOperationReturningFuture() }

@crichardson
Limiting # of simultaneous requests
val limiter =
new ConcurrencyLimiter(maxConcurrentRequests=10, maxQueueSize=30)
val resultFuture = limiter.withLimit {
asynchronousOperationReturningFuture()
}
class ConcurrencyLimiter ...
val concurrencyManager : ActorRef = ...
def withLimit[T](body : => Future[T])(...) =
(concurrencyManager ?
ConcurrentExecutionManager.Request { () => body }).mapTo[T]

@crichardson
Putting it all together
@Component
class ProductInfoServiceImpl @Autowired()(...) extends ProductService {
val limiter = new ConcurrencyLimiter(...)
val breaker = new CircuitBreaker(...)
...
breaker.withCircuitBreaker {
limiter.withLimit {
TimeoutFuture { ... AsyncRestTemplate.get ... }
}
}
}

@crichardson
Why solve this problem for JavaScript?
Browser invokes web services
Implement front-end server/API gateway using NodeJS!

@crichardson
What’s NodeJS?
Designed for DIRTy apps

@crichardson
NodeJS
JavaScript
Reactor
pattern
Modules

@crichardson
Asynchronous JavaScript code =
callback hell
Scenarios:
Sequential: A B C
Fork and join: A and B C
Code quickly becomes very messy

@crichardson
Callback-based HTTP client
request = require("request")
handler = (error, clientResponse, body) ->
if clientResponse.statusCode != 200
// ERROR
else
// SUCCESS
request("http://.../productdetails/" + productId, handler)

@crichardson
Messy callback code
getProductDetails = (req, res) ->
productId = req.params.productId
result = {productId: productId}
makeHandler = (key) ->
(error, clientResponse, body) ->
if clientResponse.statusCode != 200
res.status(clientResponse.statusCode)
res.write(body)
res.end()
else
result[key] = JSON.parse(body)
if (result.productInfo and result.recommendations and result.reviews)
res.json(result)
request("http://localhost:3000/productdetails/" + productId, makeHandler("productInfo"))
request("http://localhost:3000/recommendations/" + productId, makeHandler('recommendations'))
request("http://localhost:3000/reviews/" + productId, makeHandler('reviews'))
app.get('/productinfo/:productId', getProductInfo)
Returns a callback
function
Have all three requests
completed?

@crichardson
Simplifying code with Promises (a.k.a.
Futures)
Functions return a promise - no callback parameter
A promise represents an eventual outcome
Use a library of functions for transforming and composing promises
Promises/A+ speciﬁcation - http://promises-aplus.github.io/promises-spec

@crichardson
Basic promise API
promise2 = promise1.then(fulfilledHandler, errorHandler, ...)
called when promise1 is fulﬁlled
returns a promise or value
resolved with outcome of callback
called when promise1 is rejected
returns a promise or value

About when.js
Rich API = Promises spec + use full
extensions
Creation:
when.defer()
when.reject()...
Combinators:
all, some, join, map, reduce
Other:
Calling non-promise code
timeout
....
https://github.com/cujojs/when

@crichardson
Simpler promise-based code
rest = require("rest")
@httpClient = rest.chain(mime).chain(errorCode);
getProductInfo : (productId) ->
@httpClient
path: "http://.../productinfo/" + productId
Returns a promise
No ugly callbacks

@crichardson
Simpler promise-based code
class ProductDetailsService
getProductDetails: (productId) ->
makeProductDetails = (productInfo, recommendations, reviews) ->
details =
productId: productId
productDetails: productInfo.entity
recommendations: recommendations.entity
reviews: reviews.entity
details
responses = [@getProductInfo(productId),
@getRecommendations(productId),
@getReviews(productId)]
all(responses).spread(makeProductDetails)
Array[Promise] Promise[Array]

@crichardson
Simpler promise-based code: HTTP
handler
getProductDetails = (req, res) ->
productId = req.params.productId
succeed = (productDetails) -> res.json(productDetails)
fail = (something) ->
res.send(500, JSON.stringify(something.entity || something))
productDetailsService.
getDetails(productId).
then(succeed, fail)
app.get('/productdetails/:productId', getProductDetails)

@crichardson
Writing robust client code

@crichardson
Implementing timeouts
timeout = require("when/timeout")
withTimeout = (promise) -> timeout(300, promise)
getProductDetails = (productId) -> ... withTimeout(client(...))
Creates a new promise
Original promise must complete within 300 msec

@crichardson
Recovering from failures
getRecommendations(productId).otherwise( -> {})
Invoked to return default value if getRecommendations()
fails

@crichardson
Limiting # of concurrent requests
ConcurrencyLimiter = require("./concurrencylimiter").ConcurrencyLimiter
limiter = new ConcurrencyLimiter(maxQueueSize = 100, maxConcurrency = 10)
getProductDetails = (productId) ->
... limiter.withLimit( -> client(...))
Homegrown code

@crichardson
Circuit breaker
CircuitBreaker = require("./circuitbreaker").CircuitBreaker
productCircuitBreaker = new CircuitBreaker()
getProductDetails = (productId) ->
... productCircuitBreaker.withCircuitBreaker( -> client(...))
Homegrown code

@crichardson
Putting it all together
getProductDetails: (productId) ->
...
responses = [@getProductInfo(productId),
@getRecommendations(productId).otherwise(() -> {}),
@getReviews(productId).otherwise(() -> {})]
all(responses).spread(succeed)
getProductInfo = (productId) ->
limiter.withLimit ->
productCircuitBreaker.withCircuitBreaker ->
withTimeout client
path: "http://..../productinfo/" + productd

@crichardson
Let’s imagine you have a stream of trades
and
you need to calculate the rolling average
price of each stock

@crichardson
Spring Integration + Complex event
processing (CEP) engine is a good
choice

@crichardson
But where is the high-level abstraction
that solves this problem?

@crichardson
Future[List[T]]
Not applicable to inﬁnite streams

@crichardson
Introducing Reactive Extensions (Rx)
The Reactive Extensions (Rx) is a library for composing
asynchronous and event-based programs using
observable sequences and LINQ-style query operators.
Using Rx, developers represent asynchronous data
streams with Observables , query asynchronous
data streams using LINQ operators , and .....
https://rx.codeplex.com/

@crichardson
About RxJava
Reactive Extensions (Rx) for the JVM
Implemented in Java
Adaptors for Scala, Groovy and Clojure
https://github.com/Netﬂix/RxJava

@crichardson
RxJava core concepts
class Observable<T> {
Subscription subscribe(Observer<T> observer)
...
}
interface Observer<T> {
void onNext(T args)
void onCompleted()
void onError(Throwable e)
}
Notiﬁes
An asynchronous stream of
items
Used to unsubscribe

@crichardson
Comparing Observable to...
Observer pattern - similar but adds
Observer.onComplete()
Observer.onError()
Iterator pattern - mirror image
Push rather than pull
Future - similar but
Represents a stream of multiple values

@crichardson
Transforming Observables
Observable<T> take(int n);
Observable<T> skip(int n);
<R> Observable<R> map(Func1<T,R> func)
<R> Observable<R> flatMap(Func1<T,Observable<R>> func)
Observable<T> filter(Func1<T,java.lang.Boolean> predicate)
...
}
Scala-collection style methods

@crichardson
Transforming observables
<K> Observable<GroupedObservable<K,T>>
groupBy(Func1<T,K> keySelector)
...
}
Similar to Scala groupBy except results are emitted as items arrive
Stream of streams!

@crichardson
Combining observables
static <R,T1,T2>
Observable<R> zip(Observable<T0> o1,
Observable<T1> o2,
Func2<T1,T2,R> reduceFunction)
...
}
Invoked with pairs of items from
o1 and o2
Stream of results from
reduceFunction

@crichardson
Creating observables from data
static Observable<T> from(Iterable<T> iterable]);
static Observable<T> from(T items ...]);
static Observable<T> from(Future<T> future]);
...
}

@crichardson
Creating observables from event sources
Observable<T> o = Observable.create(
new SubscriberFunc<T> () {
Subscription onSubscribe(Observer<T> obs) {
... connect to event source....
return new Subscriber () {
void unsubscribe() { ... };
};
});
Called once for
each Observer
Called when
unsubscribing
Arranges to call obs.onNext/onComplete/...

@crichardson
Using Rx Observables instead of
Futures

@crichardson
Rx-based ProductInfoService
@Component
class ProductInfoService
val baseUrl = ...
val responseEntity =
asyncRestTemplate.getForEntity(baseUrl + "/productinfo/{productId}",
classOf[ProductInfo], productId)
toRxObservable(responseEntity).map {
(r : ResponseEntity[ProductInfo]) => r.getBody
}
}

@crichardson
ListenableFuture Observable
implicit def toRxObservable[T](future: ListenableFuture[T])
: Observable[T] = {
def create(o: Observer[T]) = {
future.addCallback(new ListenableFutureCallback[T] {
def onSuccess(result: T) {
o.onNext(result)
o.onCompleted()
}
def onFailure(t: Throwable) {
o.onError(t)
}
})
new Subscription {
def unsubscribe() {}
}
}
Observable.create(create _)
}
Supply single value
Indicate failure
Do nothing

@crichardson
Rx - ProductDetailsService
@Component
class ProductDetailsService @Autowired()
(productInfoService: ProductInfoService,
reviewService: ReviewService,
ecommendationService: RecommendationService) {
def getProductDetails(productId: Long) = {
val productInfo = productInfoService.getProductInfo(productId)
val recommendations =
recommendationService.getRecommendations(productId)
val reviews = reviewService.getReviews(productId)
Observable.zip(productInfo, recommendations, reviews,
(p : ProductInfo, r : Recommendations, rv : Reviews) =>
ProductDetails(p, r, rv))
}
}
Just like
Scala
Futures

@crichardson
Rx - ProductController
@Controller
class ProductController
@ResponseBody
def productDetails(@PathVariable productId: Long) =
toDeferredResult(productDetailsService.getProductDetails(productId))

@crichardson
Rx - Observable DeferredResult
implicit def toDeferredResult[T](observable : Observable[T]) = {
val result = new DeferredResult[T]
observable.subscribe(new Observer[T] {
def onCompleted() {}
def onError(e: Throwable) {
result.setErrorResult(e)
}
def onNext(r: T) {
result.setResult(r.asInstanceOf[T])
}
})
result
}

@crichardson
RxObservables vs. Futures
Much better than JDK 7 futures
Comparable to Scala Futures
Rx Scala code is slightly more verbose

@crichardson
Making this code robust
Hystrix works with Observables (and thread pools)
But
For event-driven code we are on our own

@crichardson
Back to the stream of Trades averaging
example...

@crichardson
AMQP messages Observables 1
<amqp:inbound-channel-adapter ... />
<int:channel id="inboundEventsChannel"/>
<int:service-activator
input-channel="inboundEventsChannel"
ref="amqpToObservableAdapter"
method="handleMessage"/>

@crichardson
AMQP messages Observables 2
class AmqpToObservableAdapter (actorRef : observerManager) {
def createObservable() =
Observable.create((o: Observer[_ >: String]) => {
observerManager ! Subscribe(o)
new Subscription {
override def unsubscribe() {
observerManager ! Unsubscribe(o)
}
}
})
def handleMessage(message : String) {
observerManager ! Message(message)
}
}
Manages and
notiﬁes observers

@crichardson
Calculating averages
Observable<AveragePrice>
calculateAverages(Observable<Trade> trades) {
...
}
class Trade {
private String symbol;
private double price;
class AveragePrice {
private String symbol;
private
double averagePrice;

@crichardson
Using groupBy()
APPL : 401 IBM : 405 CAT : 405 APPL: 403
groupBy( (trade) => trade.symbol)
APPL : 401
IBM : 405
CAT : 405 ...
APPL: 403
Observable<GroupedObservable<String, Trade>>
Observable<Trade>

@crichardson
Using window()
APPL : 401 APPL : 405 APPL : 405 ...
APPL : 401 APPL : 405 APPL : 405
APPL : 405 APPL : 405 APPL : 403
APPL : 405 ...
window(...)
Observable<Trade>
Observable<Observable<Trade>>
N secs
N secs
M secs

@crichardson
Using reduce()
APPL : 402 APPL : 405 APPL : 405
APPL : 404
reduce(sumCalc) / length
Observable<Trade>
Observable<AveragePrice> Singleton

@crichardson
Using merge()
merge()
APPL : 401
IBM : 405
CAT : 405 ...
APPL: 403
APPL : 401 IBM : 405 CAT : 405 APPL: 403
Observable<Observable<AveragePrice>>
Observable<AveragePrice>

@crichardson
RxJS / NodeJS example
var rx = require("rx");
function tailFile (fileName) {
var self = this;
var o = rx.Observable.create(function (observer) {
var watcher = self.tail(fileName, function (line) {
observer.onNext(line);
});
return function () {
watcher.close();
}
});
return o.map(parseLogLine);
}
function parseLogLine(line) { ... }

@crichardson
Rx in the browser - implementing
completion
TextChanges(input)
.DistinctUntilChanged()
.Throttle(TimeSpan.FromMilliSeconds(10))
.Select(word=>Completions(word))
.Switch()
.Subscribe(ObserveChanges(output));
Your Mouse is a Database
http://queue.acm.org/detail.cfm?id=2169076
Ajax call returning
Observable
Change events Observable
Display completions

@crichardson
Summary
Consuming web services asynchronously is essential
Scala-style composable Futures are a powerful concurrency abstraction
Rx Observables are even more powerful
Rx Observables are a unifying abstraction for a wide variety of use cases

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@crichardson chris@chrisrichardson.net
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Futures and Rx Observables: powerful abstractions for consuming web services asynchronously (#springone #s2gx)

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