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서버 개발자가 바라 본
Functional Reactive Programming
with RxJava
김대성
http://gmind7.github.io
Java Software Developer

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int a = 0;
int b = a*1;
int c = a*1;
int d = b*c;
.println(d) // 0
d
a
b c
d
b
a
Machine1
c
Machine2Actor Model
Functional Reactive Programming e.g
a = 2
.println(d) // ?
// b=2, c=2, d=4

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eXchange programming paradigm

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FP RPFRP
Functional Reactive Programming 이란?

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COMPOSABLE FUNCTIONS
REACTIVELY APPLIED
d
b
ca

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RxJava
getData();
Calling Thread
Thread Pool
Callback Thread
Observable<Data>Public

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RxJava
EVENT ITERABLE (PULL) OBSERVABLE (PUSH)
Retrieve Data onNext(T)
Discover Error onError(Exception)
Complete onCompleted()
PUSH 4 3 2 1 …..

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RxJava
>> 4 3 2 1 ….. >>
ObserverObservable
PUSH

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RxJava Hello, World!
Observable
데이터 발행 (PUSH) 하기
>> 4 3 2 1 ….. >>
PUSH
Observable<String> observable = Observable.create(
new Observable.OnSubscribe<String>() {
@Override
public void call(Subscriber<? super String> subscriber) {
subscriber.onNext("Hello, world!"); // 데이터 PUSH … next
subscriber.onCompleted(); // 데이터 PUSH 이제 그만(완료) 할게..
}
}
);

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RxJava
Observer
Hello, World!
PUSH 될 데이터 구독(소비) 계획 하기
>> 4 3 2 1 ….. >>
Subscriber<String> subscriber = new Subscriber<String>() {
@Override // 구독 계획
public void onNext(String s) { System.out.println("onNext:" + s); }
@Override // 에러 계획
public void onError(Throwable e) { System.out.println("onError:"+e.getMessage()); }
@Override // 완료 계획
public void onCompleted() { System.out.println("onComplated"); }
};

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RxJava Hello, World!
// 2. PUSH 될 데이터 구독 계획
Subscriber<String> subscriber = new Subscriber<String>() {……
// 3. 구독자가 가입 되면 데이터 발행 -> 구독 (Run)
observable.subscribe(subscriber);
// 1. PUSH 데이터 생성 (Async)
Observable<String> observable = Observable.create( ……

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RxJava Hello, World!
// java 7
Observable.just("Hello, world!").subscribe(new Action1<String>() {
@Override
public void call(String s) {
System.out.println(s);
}
});
// java 8
Observable.just("Hello, world!").subscribe(System.out::println);
// Outputs
// Hello, world!

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- Create
- Defer
- Empty / Never ..
- From
- Interval
- Just
- Range
- Repeat
- Start
- Timer
…..
- And / Then / When
- CombineLatest
- Join
- Merge
- StartWith
- Switch
- Map / FlatMap
- Zip
- Filter
- IgnoreElemets
- Last
…..
- Delay
- Do
- Materialize
- Dematerialize
- ObserveOn
- Serialize
- Subscribe
- SubscribeOn
- TimeInterval
- Timeout
…..

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@RequestMapping(value="/callable", method = RequestMethod.GET)
public Callable<Object> callableShowAll() {
Callable<Object> callable = () -> accountService.findAll();
return callable;
}
@RequestMapping(value="/rxjava", method = RequestMethod.GET)
public DeferredResult<Object> rxJavaShowAll() {
DeferredResult<Object> deferredResult = new DeferredResult<>(5000L);
Observable<List<Account>> resources = accountService.rxFindAll();
resources.subscribe(response -> {
deferredResult.setResult(response);
});
return deferredResult;
}
RxJava +

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1 2 3 4 5 6 …
recommendService
.requestRecommends(id)
RxJava +

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@RequestMapping(value="/{id}", method = RequestMethod.GET)
public DeferredResult<Object> showYourStore(@PathVariable("id") Long id) {
DeferredResult<Object> deferredResult = new DeferredResult<>();
Observable<Recommend> recommendRx = recommend.requestRecommends(id);
…..
deferredResult.setResult(response);
return deferredResult;
RxJava +

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RxJava +
public Observable<Recommend> requestRecommends(long accountId) {
return Observable.from(
RxNetty.createHttpGet("http://localhost:19080" + "/rxjava/recommend/" +
accountId)
.flatMap(response -> response.getContent().map(content ->
content.toString(Charset.defaultCharset())))
.map(data -> new Gson().fromJson(new String(data), Recommend[].class))
.toBlocking().single());
}

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1 2 3 4 5 6 …
recommendService
.requestRecommends(id)
1 2 3 4 5
unsubscribe
.take(5)
RxJava +

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@RequestMapping(value="/{id}", method = RequestMethod.GET)
public DeferredResult<Object> showYourStore(@PathVariable("id") Long id) {
DeferredResult<Object> deferredResult = new DeferredResult<>();
Observable<Recommend> recommendRx = recommend.requestRecommends(id);
recommendRx
.take(5)
…..
deferredResult.setResult(response);
return deferredResult;
RxJava +

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1 2 6 …
recommendService
.requestRecommends(id)
1 2.take(5)
.flatMap() 1 2
3
3
3
4
4
4
5
5
5
RxJava +
unsubscribe

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@RequestMapping(value="/{id}", method = RequestMethod.GET)
public DeferredResult<Object> showYourStore(@PathVariable("id") Long id) {
DeferredResult<Object> deferredResult = new DeferredResult<>();
Observable<Recommend> recommendRx = recommend.requestRecommends(id);
recommendRx
.take(3)
.flatMap(recommend -> {
…….
}
…..
deferredResult.setResult(response);
return deferredResult;
RxJava +

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1 2 3 4 5 6 …
recommendService
.requestRecommends(id)
1 2 3 4 5.take(5)
.flatMap()
goodsMetaInfo()
1 2 3 4 5
1
RxJava +
unsubscribe

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………………
.flatMap(recommend -> {
// async 1
Observable<GoodsMetaInfo> goodsMetaInfo = goodsMetaInfo.findOne(recommend.id())
……..
RxJava +

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1 2 3 4 5 6 …
recommendService
.requestRecommends(id)
1 2 3 4 5.take(5)
.flatMap()
goodsMetaInfo()
.map()
1 2 3 4 5
1
1
RxJava +
unsubscribe

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………………
.flatMap(recommend -> {
// async 1
Observable<GoodsMetaInfo> goodsMetaInfo = goodsMetaInfo.findOne(recommend.id())
.map(x -> { // 출시 1개월 이내 상품에는 [New] 타이틀 추가
boolean isNewTitle = x.createDate.isAfter(LocalDateTime.now().minusMonths(1));
if (isNewTitle) {
x.setTitle("[New] " + x.getTitle());
}
return x;
});
…….
….
})
……..
RxJava +

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1 2 3 4 5 6 …
recommendService
.requestRecommends(id)
1 2 3 4 5.take(5)
.flatMap()
goodsMetaInfo()
goodsRating()
.map()
1 2 3 4 5
1
1
1
RxJava +
unsubscribe

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RxJava
………………
.flatMap(recommend -> {
// async 1
Observable<GoodsMetaInfo> goodsMetaInfo = goodsMetaInfo.findOne(recommend.id())
.map(x -> {
boolean isNewTitle = x.createDate.isAfter(LocalDateTime.now().minusMonths(1));
if (isNewTitle) {
x.setTitle("[New] " + x.getTitle());
}
return x;
});
// async 2
Observable<GoodsRating> goodsRating = goodsRating.findOne(recommend.id());
…….
….
})
……..

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1 2 3 4 5 6 …
recommendService
.requestRecommends(id)
1 2 3 4 5.take(5)
.flatMap()
goodsMetaInfo()
goodsRating()
.map()
1 2 3 4 5
1
1
.zip()
1
1
RxJava
unsubscribe

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………………
.flatMap(recommend -> {
Observable<GoodsMetaInfo> goodsMetaInfo = goodsMetaInfo.findOne(recommend.id())
.map(x -> {
boolean isNewTitle = x.createDate.isAfter(LocalDateTime.now().minusMonths(1));
if (isNewTitle) {
x.setTitle("[New] " + x.getTitle());
}
return x;
});
Observable<GoodsRating> goodsRating = goodsRating.findOne(recommend.id());
// async 3
return Observable.zip(goodsMetaInfo, goodsRating, (x, y) -> {
Map<String, Object> map = Maps.newHashMap();
map.put("recommend", recommend);
map.put("goods", x);
map.put("rating", y);
return map;
});
})
……..
RxJava +

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1 2 3 4 5 6 …
recommendService
.requestRecommends(id)
1 2 3 4 5
unsubscribe
.take(5)
.flatMap()
goodsMetaInfo()
goodsRating()
.map()
1 2 3 4 5
1
1
.zip()
1
1
.toList() 1 2 3 4 5
RxJava +

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@RequestMapping(value="/{id}", method = RequestMethod.GET)
public DeferredResult<Object> showYourStore(@PathVariable("id") Long id) {
DeferredResult<Object> deferredResult = new DeferredResult<>();
Observable<Recommend> recommendRx = recommend.requestRecommends(id);
recommendRx
.take(3)
.flatMap(recommend -> {
……
})
.toList()
…..
return deferredResult;
RxJava +

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@RequestMapping(value="/{id}", method = RequestMethod.GET)
public DeferredResult<Object> showYourStore(@PathVariable("id") Long id) {
DeferredResult<Object> deferredResult = new DeferredResult<>();
Observable<Recommend> recommendRx = recommend.requestRecommends(id);
recommendRx
.take(3)
.flatMap(recommend -> {
……..
……..
})
.toList()
.timeout(5L, TimeUnit.SECONDS)
.subscribe(response -> {
deferredResult.setResult(response);
}, error -> {
deferredResult.setErrorResult(error);
}, () -> {
});
return deferredResult;
RxJava +

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@RequestMapping(value="/{id}", method = RequestMethod.GET)
public DeferredResult<Object> showYourStore(@PathVariable("id") Long id) {
DeferredResult<Object> deferredResult = new DeferredResult<>();
Observable<Recommend> recommendRx = recommend.requestRecommends(id);
recommendRx
.take(3)
.flatMap(recommend -> {
……..
……..
})
.toList()
.timeout(5L, TimeUnit.SECONDS)
.subscribe(response -> {
deferredResult.setResult(response);
}, error -> {
deferredResult.setErrorResult(error);
}, () -> {
});
return deferredResult;
RxJava +

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………………
.flatMap(recommend -> {
Observable<GoodsMetaInfo> goodsMetaInfo = goodsMetaInfo.findOne(recommend.id())
…
.subscribeOn(Schedulers.computation());
Observable<GoodsRating> goodsRating = goodsRating.findOne(recommend.id())
…
.subscribeOn(Schedulers.computation());
return Observable.zip(goodsMetaInfo, goodsRating, (x, y) -> {
…
return map;
}).subscribeOn(Schedulers.computation());
})
……..
RxJava +

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ERROR

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@RequestMapping(value="/{id}", method = RequestMethod.GET)
public DeferredResult<Object> showYourStore(@PathVariable("id") Long id) {
DeferredResult<Object> deferredResult = new DeferredResult<>();
Observable<Recommend> recommendRx = recommend.requestRecommends(id);
recommendRx
.take(3)
.flatMap(recommend -> {
Observable<GoodsMetaInfo> goodsMetaInfo = goodsMetaInfo….
…
Observable<GoodsRating> goodsRating = goodsRating…
…
})
.toList()
.timeout(5L, TimeUnit.SECONDS)
.subscribe(response -> {
deferredResult.setResult(response);
}, error -> {
deferredResult.setErrorResult(error);
}, () -> {
});
return deferredResult;
RxJava +

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RxJava +
request
Netty
tcpwrite
response
tcpwrite
public Channel…
@Override
public void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
Account message = new Account(1);
Observable<Object> observable = clientReqHandler.request(ctx.channel(), message);
observable.subscribe(response -> {
ctx.channel().writeAndFlush(response);
});
}
?
tcpread
public void…

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RxJava + Netty
public class ClientRequestHandler extends SimpleChannelInboundHandler<Object> {
private final ConcurrentHashMap QUEUE
= new ConcurrentHashMap<String, Subscriber<?>>;
public ClientRequestHandler(){
}

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RxJava + Netty
public Observable<Object> request(final Channel channel, final Object message) {
return Observable.<Object>create(suscriber -> {
this.QUEUE.put("requestId", suscriber);
channel.writeAndFlush(message);
})
.timeout(5L, TimeUnit.SECONDS)
.finallyDo(() -> queue.remove("requestId")});
};
@Override
protected void channelRead0(ChannelHandlerContext channelHandlerContext, Object
object) throws Exception {
Subscriber subscriber = (Subscriber)this.QUEUE.remove("requestId");
if(subscriber==null) return;
subscriber.onNext(object);
subscriber.onCompleted();
}

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RxJava + Netty
@Override
public void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
Account message = new Account(1);
Observable<Object> observable = clientReqHandler.request(ctx.channel(), message);
observable.subscribe(response -> {
ctx.channel().writeAndFlush(response);
});
}
request1
tcpwrite
response1
tcpwrite
public void…tcpread
public void…

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52.
OOP
CACHE
RDBMS
1995 2015
HADOOP
NOSQL
FP, RX, FRP …
지금은 POLYGLOT 시대…

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http://www.manning.com/blackheath
http://www.slideshare.net/InfoQ/functional-reactive-programming-in-the-netflix-api
https://youtu.be/-P28LKWTzrI
Towards Reactive Programming for Object-oriented Applications.pdf
http://www.slideshare.net/misgod/functional-41887638
http://ent.hankyung.com/news/app/newsview.php?aid=2014112839734

54.
감사합니다