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Sortir de l’Enfer des Callbacks RxJava + Java 8

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@SimonBasle @Couchbase @InfoQFR @bbl_fr

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L‘Enfer des Callbacks?

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L‘Enfer des Callbacks?

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synchrone == inefficace*

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nous avons besoin de code asynchrone

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nous avons besoin de code asynchrone réactif

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nous avons besoin de code asynchrone parallélisable

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nous avons besoin de code asynchrone composable

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nous avons besoin de code asynchrone lisible

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mais comment bien faire Asynchrone ?

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les Futures

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les Futures une modélisation lisible

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les Futures peuvent bloquer (get)

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les Futures deviennent compliquées au delà d’un niveau

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les Futures se composent mal

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les Callbacks

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les Callbacks tout simple

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les Callbacks pas de blocage possible

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les Callbacks ne se composent pas

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les Callbacks deviennent vite illisibles

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EXEMPLE : je veux mes 10 premiers docs marqués comme favoris sous forme de json complet

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Pour ça je dois agréger en asynchrone : méta commentaires & auteurs description d’images

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DocumentService.find("userId", new Callback>() { public void onSuccess(List result) { final List jsonList = new ArrayList(10); int taken = 0; for (Document doc : result) { if (taken >= 10) break; if (!doc.isStarred()) continue; taken++; final CountDownLatch rendezVous = new CountDownLatch(3); final JsonObject jsonBuffer = new JsonObject(); jsonBuffer.appendInt("id", doc.getId()); jsonBuffer.append("text", doc.getText()); CommentService.findForDoc(doc, new Callback>() { public void onSuccess(List comments) { final JsonObject commentArray = JsonObject.createArray(); CountDownLatch userLatch = new CountDownLatch(comments.size()); for (Comment c : comments) { JsonObject cj = new JsonObject(); cj.append("content", c.getText()); cj.append("date", c.getDate()); UserService.find(c.getUserId(), new Callback() { public void onSuccess(User user) { cj.append("author", user.getName()); cj.append("nickname", user.getLogin()); cj.append("email", user.getEmail()); // …

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// … continued commentArray.add(cj); userLatch.countDown(); } }); } userLatch.await(); jsonBuffer.addArray("comments", commentArray); rendezVous.countDown(); } }); MetaService.findForDoc(doc, new Callback>() { public void onSuccess(List metas) { jsonBuffer.addArray("meta", jsonify(metas)); rendezVous.countDown(); } }); PictureService.findAllMetas(doc.getPictures(), new Callback>() { public void onSuccess(List picMetas) { jsonBuffer.addArray("pictures", jsonify(picMetas)); rendezVous.countDown(); } }); rendezVous.await(); jsonList.add(jsonBuffer.toString()); } somethingToDo.onSuccess(jsonList); } });

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2 slides en taille 10 58 lignes de code max 7 tabulations

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jusqu’à 3 Callbacks imbriqués 2 usages de CountDownLatch

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DocumentService.find("userId", new Callback>() { public void onSuccess(List result) { final List jsonList = new ArrayList(10); int taken = 0; for (Document doc : result) { if (taken >= 10) break; if (!doc.isStarred()) continue; taken++; final CountDownLatch rendezVous = new CountDownLatch(3); final JsonObject jsonBuffer = new JsonObject(); jsonBuffer.appendInt("id", doc.getId()); jsonBuffer.append("text", doc.getText()); CommentService.findForDoc(doc, new Callback>() { public void onSuccess(List comments) { final JsonObject commentArray = JsonObject.createArray(); CountDownLatch userLatch = new CountDownLatch(comments.size()); for (Comment c : comments) { JsonObject cj = new JsonObject(); cj.append("content", c.getText()); cj.append("date", c.getDate()); UserService.find(c.getUserId(), new Callback() { public void onSuccess(User user) { cj.append("author", user.getName()); cj.append("nickname", user.getLogin()); cj.append("email", user.getEmail()); // … THIS

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IS DocumentService.find("userId", new Callback>() { public void onSuccess(List result) { final List jsonList = new ArrayList(10); int taken = 0; for (Document doc : result) { if (taken >= 10) break; if (!doc.isStarred()) continue; taken++; final CountDownLatch rendezVous = new CountDownLatch(3); final JsonObject jsonBuffer = new JsonObject(); jsonBuffer.appendInt("id", doc.getId()); jsonBuffer.append("text", doc.getText()); CommentService.findForDoc(doc, new Callback>() { public void onSuccess(List comments) { final JsonObject commentArray = JsonObject.createArray(); CountDownLatch userLatch = new CountDownLatch(comments.size()); for (Comment c : comments) { JsonObject cj = new JsonObject(); cj.append("content", c.getText()); cj.append("date", c.getDate()); UserService.find(c.getUserId(), new Callback() { public void onSuccess(User user) { cj.append("author", user.getName()); cj.append("nickname", user.getLogin()); cj.append("email", user.getEmail()); // …

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callback DocumentService.find("userId", new Callback>() { public void onSuccess(List result) { final List jsonList = new ArrayList(10); int taken = 0; for (Document doc : result) { if (taken >= 10) break; if (!doc.isStarred()) continue; taken++; final CountDownLatch rendezVous = new CountDownLatch(3); final JsonObject jsonBuffer = new JsonObject(); jsonBuffer.appendInt("id", doc.getId()); jsonBuffer.append("text", doc.getText()); CommentService.findForDoc(doc, new Callback>() { public void onSuccess(List comments) { final JsonObject commentArray = JsonObject.createArray(); CountDownLatch userLatch = new CountDownLatch(comments.size()); for (Comment c : comments) { JsonObject cj = new JsonObject(); cj.append("content", c.getText()); cj.append("date", c.getDate()); UserService.find(c.getUserId(), new Callback() { public void onSuccess(User user) { cj.append("author", user.getName()); cj.append("nickname", user.getLogin()); cj.append("email", user.getEmail()); // …

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HEEEELL! DocumentService.find("userId", new Callback>() { public void onSuccess(List result) { final List jsonList = new ArrayList(10); int taken = 0; for (Document doc : result) { if (taken >= 10) break; if (!doc.isStarred()) continue; taken++; final CountDownLatch rendezVous = new CountDownLatch(3); final JsonObject jsonBuffer = new JsonObject(); jsonBuffer.appendInt("id", doc.getId()); jsonBuffer.append("text", doc.getText()); CommentService.findForDoc(doc, new Callback>() { public void onSuccess(List comments) { final JsonObject commentArray = JsonObject.createArray(); CountDownLatch userLatch = new CountDownLatch(comments.size()); for (Comment c : comments) { JsonObject cj = new JsonObject(); cj.append("content", c.getText()); cj.append("date", c.getDate()); UserService.find(c.getUserId(), new Callback() { public void onSuccess(User user) { cj.append("author", user.getName()); cj.append("nickname", user.getLogin()); cj.append("email", user.getEmail()); // …

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Wow Such Space! DocumentService.find("userId", new Callback>() { public void onSuccess(List result) { final List jsonList = new ArrayList(10); int taken = 0; for (Document doc : result) { if (taken >= 10) break; if (!doc.isStarred()) continue; taken++; final CountDownLatch rendezVous = new CountDownLatch(3); final JsonObject jsonBuffer = new JsonObject(); jsonBuffer.appendInt("id", doc.getId()); jsonBuffer.append("text", doc.getText()); CommentService.findForDoc(doc, new Callback>() { public void onSuccess(List comments) { final JsonObject commentArray = JsonObject.createArray(); CountDownLatch userLatch = new CountDownLatch(comments.size()); for (Comment c : comments) { JsonObject cj = new JsonObject(); cj.append("content", c.getText()); cj.append("date", c.getDate()); UserService.find(c.getUserId(), new Callback() { public void onSuccess(User user) { cj.append("author", user.getName()); cj.append("nickname", user.getLogin()); cj.append("email", user.getEmail()); // …

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RxJava

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RxJava

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Netflix OpenSource

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le pendant du Iterable - Iterator

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Iterable - Iterator devient Observable - Observer

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Iterable - Iterator devient Observable - Observer “Pull” “Push”

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composer

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composer des programmes asynchrones basés sur les événements

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composer des programmes asynchrones basés sur les événements en utilisant des séquences observables

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abstraire l’aspect concurrent

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tout est Observable sous le capot : pool de threads, acteurs, peu importe

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Flexibilité ...on gère...

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Flexibilité ...on gère... les valeurs uniques

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Flexibilité ...on gère... les séquences

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Flexibilité ...on gère... les flux infinis

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Flexibilité 3-en-1

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the Reactive Manifesto reactivemanifesto.org

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reactive-streams.org standardiser sur la jvm

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reactive-streams.org standardiser sur la jvm akka - reactor - rxjava

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Montre-moi Comment ça Marche !

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interface Observer

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interface Observer onNext(T data)

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interface Observer onNext(T data) onCompleted()

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interface Observer onNext(T data) onCompleted() onError(Throwable t)

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interface Observer onNext(T data) onCompleted() onError(Throwable t)

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Observable

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Observable implémenté ou créé

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Observable Observable.from(T… values);

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Observable Observable.from(Iterable itrbl);

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Observable Observable.just(T oneValue);

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Observable Observable.range(int start, int count);

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Observable permet de s’abonner

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Observable monObservable.subscribe(someObserver);

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Observable permet de composer

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diagrammes “à billes”

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beaucoup de diagrammes “à billes”

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Transformation

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Observable map(Func1 func)

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Observable map(Func1 func)

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Observable flatMap(Func1> func)

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Observable flatMap(Func1> func)

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Observable> buffer(int count)

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Observable> buffer(int count)

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Observable reduce(Func2 accumulator)

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Observable reduce(Func2 accumulator)

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Observable scan(Func2 accumulator)

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Observable scan(Func2 accumulator)

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Filtrage

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Observable take(int n)

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Observable take(int n)

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Observable skip(int n)

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Observable skip(int n)

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Observable filter(Func1 predicate)

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Observable filter(Func1 predicate)

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Observable sample(long period, TimeUnit unit)

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Observable sample(long period, TimeUnit unit)

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Observable distinct()

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Observable distinct()

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Combinaison

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static Observable concat(Observable t1, Observable t2)

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static Observable concat(Observable t1, Observable t2)

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static Observable merge(Observable t1, Observable t2)

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static Observable merge(Observable t1, Observable t2)

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Observable zip(Observable other, Func2 zipFunction)

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Observable zip(Observable other, Func2 zipFunction)

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Parallélisme

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Observable subscribeOn(Scheduler workThere)

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Observable subscribeOn(Scheduler workThere)

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Observable observeOn(Scheduler workThere)

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Observable observeOn(Scheduler workThere)

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Observable cache()

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Observable cache()

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...

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Tellement de Choix !

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Observable permet de gérer les erreurs

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On a déjà la méthode onError(Throwable t) dans Observer ...

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...mais on peut aussi les gérer différemment

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static Observable mergeDelayError( Observable t1, Observable t2)

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static Observable mergeDelayError( Observable t1, Observable t2)

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Observable onErrorReturn(Func1 fallbackFunction)

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Observable onErrorReturn(Func1 fallbackFunction)

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Observable onErrorResumeNext(Observable fallback)

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Observable onErrorResumeNext(Observable fallback)

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Observable retry(int retryCount)

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Observable retry(int retryCount)

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Je suis perdu ça donne quoi concrètement ?

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Observable fullDocumentJson = DocumentService.find("user") .filter(new Func1() { public Boolean call(Document doc) { return doc.isStarred(); }}) .take(10) .map(new Func1() { public JsonObject call(Document doc) { Observable oc = CommentService.findForDoc(doc) .flatMap(new Func1>() { public Observable call(Comment c) { return UserService.find(c.getUserId()) .first() .map(new Func1() { public JsonObject call(User u) { JsonObject result = jsonify(c) .append("author", u.getName()); return result.append("nickname", u.getLogin()) .append("email", u.getEmail()); }}); }}); Observable om = MetaService.findForDoc(doc) .map(new Func1() { public JsonObject call(Meta m) { return jsonify(m); }});

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Observable op = PictureService.findAllMetas(doc.getPictures()) .map(new Func1() { public JsonObject call(PicMeta p) { return jsonify(p); }}); Func2 arrayAggregator = new Func2() { public JsonArray call(JsonArray t1, JsonObject t2) { return t1.addElement(t2); }}; JsonObject docJson = new JsonObject().appendInt("id", doc.getId()).append("text", doc.getText()); JsonArray c = new JsonArray(); docJson.addArray("comments", c); oc.reduce(c, arrayAggregator); JsonArray m = new JsonArray(); docJson.addArray("meta", m); om.reduce(m, arrayAggregator); JsonArray p = new JsonArray(); docJson.addArray("pictures", p); op.reduce(p, arrayAggregator); return docJson; } });

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On voit toujours rien #CallBackHell @simonbasle

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Observable fullDocumentJson = DocumentService.find("user") .filter(new Func1() { public Boolean call(Document doc) { return doc.isStarred(); }}) .take(10) .map(new Func1() { public JsonObject call(Document doc) { Observable oc = CommentService.findForDoc(doc) .flatMap(new Func1>() { public Observable call(Comment c) { return UserService.find(c.getUserId()) .first() .map(new Func1() { public JsonObject call(User u) { JsonObject result = jsonify(c) .append("author", u.getName()); return result.append("nickname", u.getLogin()) .append("email", u.getEmail()); }}); }}); Observable om = MetaService.findForDoc(doc) .map(new Func1() { public JsonObject call(Meta m) { return jsonify(m); }});

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Observable op = PictureService.findAllMetas(doc.getPictures()) .map(new Func1() { public JsonObject call(PicMeta p) { return jsonify(p); }}); Func2 arrayAggregator = new Func2() { public JsonArray call(JsonArray t1, JsonObject t2) { return t1.addElement(t2); }}; JsonObject docJson = new JsonObject().appendInt("id", doc.getId()).append("text", doc.getText()); JsonArray c = new JsonArray(); docJson.addArray("comments", c); oc.reduce(c, arrayAggregator); JsonArray m = new JsonArray(); docJson.addArray("meta", m); om.reduce(m, arrayAggregator); JsonArray p = new JsonArray(); docJson.addArray("pictures", p); op.reduce(p, arrayAggregator); return docJson; } });

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filter on doc.isStarred()

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take(10)

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map( meta to Json)

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map( pictures to Json)

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map( comments to Json)

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map( comments to Json) flattened with User

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reduce streams of Json to single arrays

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c’est mieux structuré et on a pas mal de bruit en fait Mmh OK

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Java 8 la cerise sur le gâteau

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Java 8 la cerise sur le gâteau

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la version hyper courte

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la version hyper courte

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la version hyper courte

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fonctions de 1ère classe

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interfaces fonctionnelles public interface Func1 { public B call(A from); }

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interfaces fonctionnelles public interface Func1 { public B call(A from); } // ^ une méthode unique

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classes anonymes

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classes anonymes LAM BDAS

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lambdas

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new Func1() { public Integer call(String from) { return from.length(); } } lambdas

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(String s) -> { return s.length(); } lambdas

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s -> s.length() lambdas

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références de méthodes

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références de méthodes MaClasse::méthodeStatique

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références de méthodes monInstance::méthodeInstance

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références de méthodes UnType::méthodeInstanceDuType

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références de méthodes String::length

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on va pouvoir éliminer le code superflu

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Observable fullDocumentJson = DocumentService.find("user") .filter(new Func1() { public Boolean call(Document doc) { return doc.isStarred(); } });

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Observable fullDocumentJson = DocumentService.find("user") .filter(doc -> doc.isStarred());

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Observable fullDocumentJson = DocumentService.find("user") .filter(Document::isStarred);

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Observable fullDocumentJson = DocumentService.find("user") .filter(Document::isStarred) .take(10) .map(doc -> { Observable oc = CommentService.findForDoc(doc) .flatMap(c -> UserService.find(c.getUserId()) .first() .map(u -> { JsonObject result = jsonify(c).append("author", u.getName()); return result.append("nickname", u.getLogin()).append("email", u.getEmail()); })); Observable om = MetaService.findForDoc(doc).map(m -> jsonify(m)); Observable op = PictureService.findAllMetas(doc.getPictures()).map(p -> jsonify(p)); JsonObject docJson = new JsonObject().appendInt("id", doc.getId()).append("text", doc.getText()); JsonArray c = new JsonArray(); docJson.addArray("comments", c); oc.reduce(c, (array, elem) -> array.addElement(elem)); JsonArray m = new JsonArray(); docJson.addArray("meta", m); om.reduce(m, (array, elem) -> array.addElement(elem)); JsonArray p = new JsonArray(); docJson.addArray("pictures", p); op.reduce(p, (array, elem) -> array.addElement(elem)); return docJson; });

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Observable fullDocumentJson = DocumentService.find("user") .filter(Document::isStarred) .take(10) .map(doc -> { Observable oc = CommentService.findForDoc(doc) .flatMap(c -> UserService.find(c.getUserId()) .first() .map(u -> { JsonObject result = jsonify(c).append("author", u.getName()); return result.append("nickname", u.getLogin()).append("email", u.getEmail()); })); Observable om = MetaService.findForDoc(doc).map(m -> jsonify(m)); Observable op = PictureService.findAllMetas(doc.getPictures()).map(p -> jsonify(p)); JsonObject docJson = new JsonObject().appendInt("id", doc.getId()).append("text", doc.getText()); JsonArray c = new JsonArray(); docJson.addArray("comments", c); oc.reduce(c, (array, elem) -> array.addElement(elem)); JsonArray m = new JsonArray(); docJson.addArray("meta", m); om.reduce(m, (array, elem) -> array.addElement(elem)); JsonArray p = new JsonArray(); docJson.addArray("pictures", p); op.reduce(p, (array, elem) -> array.addElement(elem)); return docJson; }); Observable fullDocumentJson = DocumentService.find("user") .filter(Document::isStarred) .take(10)

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Observable fullDocumentJson = DocumentService.find("user") .filter(Document::isStarred) .take(10) .map(doc -> { Observable oc = CommentService.findForDoc(doc) .flatMap(c -> UserService.find(c.getUserId()) .first() .map(u -> { JsonObject result = jsonify(c).append("author", u.getName()); return result.append("nickname", u.getLogin()).append("email", u.getEmail()); })); Observable om = MetaService.findForDoc(doc).map(m -> jsonify(m)); Observable op = PictureService.findAllMetas(doc.getPictures()).map(p -> jsonify(p)); JsonObject docJson = new JsonObject().appendInt("id", doc.getId()).append("text", doc.getText()); JsonArray c = new JsonArray(); docJson.addArray("comments", c); oc.reduce(c, (array, elem) -> array.addElement(elem)); JsonArray m = new JsonArray(); docJson.addArray("meta", m); om.reduce(m, (array, elem) -> array.addElement(elem)); JsonArray p = new JsonArray(); docJson.addArray("pictures", p); op.reduce(p, (array, elem) -> array.addElement(elem)); return docJson; }); Observable oc = CommentService.findForDoc(doc) .flatMap(c -> UserService.find(c.getUserId()) .first() .map(u -> { JsonObject result = jsonify(c) .append("author", u.getName()); .append("nickname", u.getLogin()) .append("email", u.getEmail()); return result; }) );

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Observable fullDocumentJson = DocumentService.find("user") .filter(Document::isStarred) .take(10) .map(doc -> { Observable oc = CommentService.findForDoc(doc) .flatMap(c -> UserService.find(c.getUserId()) .first() .map(u -> { JsonObject result = jsonify(c).append("author", u.getName()); return result.append("nickname", u.getLogin()).append("email", u.getEmail()); })); Observable om = MetaService.findForDoc(doc).map(m -> jsonify(m)); Observable op = PictureService.findAllMetas(doc.getPictures()).map(p -> jsonify(p)); JsonObject docJson = new JsonObject().appendInt("id", doc.getId()).append("text", doc.getText()); JsonArray c = new JsonArray(); docJson.addArray("comments", c); oc.reduce(c, (array, elem) -> array.addElement(elem)); JsonArray m = new JsonArray(); docJson.addArray("meta", m); om.reduce(m, (array, elem) -> array.addElement(elem)); JsonArray p = new JsonArray(); docJson.addArray("pictures", p); op.reduce(p, (array, elem) -> array.addElement(elem)); return docJson; }); oc.reduce(c, (array, elem) -> array.addElement(elem));

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2 1 slides en taille 10 58 23 lignes de code max 7 3 tabulations 3 0 imbrications

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on a bien dégrossi notre code

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ah oui mais moi j’ai que Java 5/6/7 5

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Projet RetroLambda https://github.com/orfjackal/retrolambda

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now I’m Batman

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TakeAway

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du code Asynchrone

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sans Callbacks

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avec un minimum de pollution visuelle

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lisible et compréhensible

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Hope you’ll love it too !

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No content

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Merci!

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Crédits ➔ The Door to Hell - By-Sa Flydime http://www.flickr.com/photos/flydime/4671890969 ➔ Cat Attack - By-Nc Static416 http://www.flickr.com/photos/ehacke/4584255926/ ➔ Série Stormtroopers - By J.D. Hancock http://photos.jdhancock.com/series/stormtroopers.html ➔ Marbles Reflected - By ~Pawsitive~Candie_N http://www.flickr.com/photos/scjn/4274713988/ ➔ Marble Diagrams - Apache 2.0 Netflix OSS http://netflix.github.io/ (doc RxJava) ➔ Chien de près - By Rpavich http://www.flickr.com/photos/rpavich/11409595543/ ➔ Hyperspace - By Procsilas Moscas http://www.flickr.com/photos/procsilas/ 12821454664/ ➔ Takeaway - By Edimbhurg Blog http://www.flickr.com/photos/theedinburghblog/ 6493647769/ ➔ The End Sable - Cc0 Elektro-Plan http://pixabay.com/p-283407/