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@julienviet Julien Viet Inter-Reactive Kotlin Applications

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Julien Viet Open source developer for 15+ years Current @vertx_project lead Principal software engineer at Marseille Java User Group Leader https://www.julienviet.com/ http://github.com/vietj @julienviet

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Outline ✓ Reactive applications ✓ Going event driven ✓ Going interactive with coroutines ✓ Streaming with channels ✓ Coroutines vs RxJava

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No content

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Application

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Software Messages Requests Metrics Availability

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Reactive systems Reactive streams Reactive programming Reactive “Responding to stimuli” Manifesto, Actor, Messages Resilience, Elasticity, Scalability, Asynchronous, non-blocking Data flow Back-pressure Non-blocking Data flow Events, Observable Spreadsheets Akka, Vert.x Akka Streams, Rx v2, Reactor, Vert.x Reactor, Reactive Spring, RxJava, Vert.x

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Eclipse Vert.x Open source project started in 2012 Eclipse / Apache licensing A toolkit for building reactive applications for the JVM 7K ⋆ on Built on top of https://vertx.io @vertx_project

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Going event driven

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while (isRunning) { val line = bufferedReader.readLine() when (line) { "ECHO" !-> bufferedWriter.write(line) !// !!... !// Other cases (!!...) !// !!... else !-> bufferedWriter.write("Unknown command") } }

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x 1000 = Ǚ

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C1 “When you have a line of text, call C2” Something else with no blocking call either C2

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Events Thread Event Loop

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 2 event-loops per CPU core by default

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Movie rating application router { get("/movie/:id") { ctx !-> getMovie(ctx) } post("/rate/:id") { ctx !-> rateMovie(ctx) } get("/rating/:id") { ctx !-> getRating(ctx) } }

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Movie rating application router { get("/movie/:id") { ctx !-> getMovie(ctx) } post("/rate/:id") { ctx !-> rateMovie(ctx) } get("/rating/:id") { ctx !-> getRating(ctx) } }

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fun getMovie(ctx: RoutingContext) { val id = ctx.pathParam("id") val params = json { array(id) } client.queryWithParams("SELECT TITLE FROM MOVIE WHERE ID=?", params) { if (it.succeeded()) { val result = it.result() if (result.rows.size !== 1) { ctx.response().end(json { obj("id" to id, "title" to result.rows[0]["TITLE"]).encode() }) } else { ctx.response().setStatusCode(404).end() } } else { ctx.fail(it.cause()) } } }

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fun getMovie(ctx: RoutingContext) { val id = ctx.pathParam("id") val params = json { array(id) } client.queryWithParams("SELECT TITLE FROM MOVIE WHERE ID=?", params) { if (it.succeeded()) { val result = it.result() if (result.rows.size !== 1) { ctx.response().end(json { obj("id" to id, "title" to result.rows[0]["TITLE"]).encode() }) } else { ctx.response().setStatusCode(404).end() } } else { ctx.fail(it.cause()) } } }

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fun getMovie(ctx: RoutingContext) { val id = ctx.pathParam("id") val params = json { array(id) } client.queryWithParams("SELECT TITLE FROM MOVIE WHERE ID=?", params) { if (it.succeeded()) { val result = it.result() if (result.rows.size !== 1) { ctx.response().end(json { obj("id" to id, "title" to result.rows[0]["TITLE"]).encode() }) } else { ctx.response().setStatusCode(404).end() } } else { ctx.fail(it.cause()) } } }

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fun getMovie(ctx: RoutingContext) { val id = ctx.pathParam("id") val params = json { array(id) } client.queryWithParams("SELECT TITLE FROM MOVIE WHERE ID=?", params) { if (it.succeeded()) { val result = it.result() if (result.rows.size !== 1) { ctx.response().end(json { obj("id" to id, "title" to result.rows[0]["TITLE"]).encode() }) } else { ctx.response().setStatusCode(404).end() } } else { ctx.fail(it.cause()) } } }

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Movie rating application router { get("/movie/:id") { ctx !-> getMovie(ctx) } post("/rate/:id") { ctx !-> rateMovie(ctx) } get("/rating/:id") { ctx !-> getRating(ctx) } }

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val movie = ctx.pathParam("id") val rating = Integer.parseInt(ctx.queryParam("getRating")[0]) client.getConnection { if (it.succeeded()) { val connection = it.result() val queryParams = json { array(movie) } connection.queryWithParams("SELECT TITLE FROM MOVIE WHERE ID=?", queryParams) { if (it.succeeded()) { val result = it.result() if (result.rows.size !== 1) { val updateParams = json { array(rating, movie) } connection.updateWithParams("INSERT INTO RATING (VALUE, MOVIE_ID) VALUES ?, ?", updateParams) { if (it.succeeded()) { ctx.response().setStatusCode(201).end() } else { connection.close() ctx.fail(it.cause()) } } } else { connection.close() ctx.response().setStatusCode(404).end() } } else { connection.close() ctx.fail(it.cause()) } } } else { ctx.fail(it.cause()) } }

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val movie = ctx.pathParam("id") val rating = Integer.parseInt(ctx.queryParam("getRating")[0]) client.getConnection { if (it.succeeded()) { val connection = it.result() val queryParams = json { array(movie) } connection.queryWithParams("SELECT TITLE FROM MOVIE WHERE ID=?", queryParams) { if (it.succeeded()) { val result = it.result() if (result.rows.size !== 1) { val updateParams = json { array(rating, movie) } connection.updateWithParams("INSERT INTO RATING (VALUE, MOVIE_ID) VALUES ?, ?", updateParams) { if (it.succeeded()) { ctx.response().setStatusCode(201).end() } else { connection.close() ctx.fail(it.cause()) } } } else { connection.close() ctx.response().setStatusCode(404).end() } } else { connection.close() ctx.fail(it.cause()) } } } else { ctx.fail(it.cause()) } }

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val movie = ctx.pathParam("id") val rating = Integer.parseInt(ctx.queryParam("getRating")[0]) client.getConnection { if (it.succeeded()) { val connection = it.result() val queryParams = json { array(movie) } connection.queryWithParams("SELECT TITLE FROM MOVIE WHERE ID=?", queryParams) { if (it.succeeded()) { val result = it.result() if (result.rows.size !== 1) { val updateParams = json { array(rating, movie) } connection.updateWithParams("INSERT INTO RATING (VALUE, MOVIE_ID) VALUES ?, ?", updateParams) { if (it.succeeded()) { ctx.response().setStatusCode(201).end() } else { connection.close() ctx.fail(it.cause()) } } } else { connection.close() ctx.response().setStatusCode(404).end() } } else { connection.close() ctx.fail(it.cause()) } } } else { ctx.fail(it.cause()) } }

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val movie = ctx.pathParam("id") val rating = Integer.parseInt(ctx.queryParam("getRating")[0]) client.getConnection { if (it.succeeded()) { val connection = it.result() val queryParams = json { array(movie) } connection.queryWithParams("SELECT TITLE FROM MOVIE WHERE ID=?", queryParams) { if (it.succeeded()) { val result = it.result() if (result.rows.size !== 1) { val updateParams = json { array(rating, movie) } connection.updateWithParams("INSERT INTO RATING (VALUE, MOVIE_ID) VALUES ?, ?", updateParams) { if (it.succeeded()) { ctx.response().setStatusCode(201).end() } else { connection.close() ctx.fail(it.cause()) } } } else { connection.close() ctx.response().setStatusCode(404).end() } } else { connection.close() ctx.fail(it.cause()) } } } else { ctx.fail(it.cause()) } }

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val movie = ctx.pathParam("id") val rating = Integer.parseInt(ctx.queryParam("getRating")[0]) client.getConnection { if (it.succeeded()) { val connection = it.result() val queryParams = json { array(movie) } connection.queryWithParams("SELECT TITLE FROM MOVIE WHERE ID=?", queryParams) { if (it.succeeded()) { val result = it.result() if (result.rows.size !== 1) { val updateParams = json { array(rating, movie) } connection.updateWithParams("INSERT INTO RATING (VALUE, MOVIE_ID) VALUES ?, ?", updateParams) { if (it.succeeded()) { ctx.response().setStatusCode(201).end() } else { connection.close() ctx.fail(it.cause()) } } } else { connection.close() ctx.response().setStatusCode(404).end() } } else { connection.close() ctx.fail(it.cause()) } } } else { ctx.fail(it.cause()) } }

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val movie = ctx.pathParam("id") val rating = Integer.parseInt(ctx.queryParam("getRating")[0]) client.getConnection { if (it.succeeded()) { val connection = it.result() val queryParams = json { array(movie) } connection.queryWithParams("SELECT TITLE FROM MOVIE WHERE ID=?", queryParams) { if (it.succeeded()) { val result = it.result() if (result.rows.size !== 1) { val updateParams = json { array(rating, movie) } connection.updateWithParams("INSERT INTO RATING (VALUE, MOVIE_ID) VALUES ?, ?", updateParams) { if (it.succeeded()) { ctx.response().setStatusCode(201).end() } else { connection.close() ctx.fail(it.cause()) } } } else { connection.close() ctx.response().setStatusCode(404).end() } } else { connection.close() ctx.fail(it.cause()) } } } else { ctx.fail(it.cause()) } }

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val movie = ctx.pathParam("id") val rating = Integer.parseInt(ctx.queryParam("getRating")[0]) client.getConnection { if (it.succeeded()) { val connection = it.result() val queryParams = json { array(movie) } connection.queryWithParams("SELECT TITLE FROM MOVIE WHERE ID=?", queryParams) { if (it.succeeded()) { val result = it.result() if (result.rows.size !== 1) { val updateParams = json { array(rating, movie) } connection.updateWithParams("INSERT INTO RATING (VALUE, MOVIE_ID) VALUES ?, ?", updateParams) { if (it.succeeded()) { ctx.response().setStatusCode(201).end() } else { connection.close() ctx.fail(it.cause()) } } } else { connection.close() ctx.response().setStatusCode(404).end() } } else { connection.close() ctx.fail(it.cause()) } } } else { ctx.fail(it.cause()) } }

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val movie = ctx.pathParam("id") val rating = Integer.parseInt(ctx.queryParam("getRating")[0]) client.getConnection { if (it.succeeded()) { val connection = it.result() val queryParams = json { array(movie) } connection.queryWithParams("SELECT TITLE FROM MOVIE WHERE ID=?", queryParams) { if (it.succeeded()) { val result = it.result() if (result.rows.size !== 1) { val updateParams = json { array(rating, movie) } connection.updateWithParams("INSERT INTO RATING (VALUE, MOVIE_ID) VALUES ?, ?", updateParams) { if (it.succeeded()) { ctx.response().setStatusCode(201).end() } else { connection.close() ctx.fail(it.cause()) } } } else { connection.close() ctx.response().setStatusCode(404).end() } } else { connection.close() ctx.fail(it.cause()) } } } else { ctx.fail(it.cause()) } }

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val movie = ctx.pathParam("id") val rating = Integer.parseInt(ctx.queryParam("getRating")[0]) client.getConnection { if (it.succeeded()) { val connection = it.result() val queryParams = json { array(movie) } connection.queryWithParams("SELECT TITLE FROM MOVIE WHERE ID=?", queryParams) { if (it.succeeded()) { val result = it.result() if (result.rows.size !== 1) { val updateParams = json { array(rating, movie) } connection.updateWithParams("INSERT INTO RATING (VALUE, MOVIE_ID) VALUES ?, ?", updateParams) { if (it.succeeded()) { ctx.response().setStatusCode(201).end() } else { connection.close() ctx.fail(it.cause()) } } } else { connection.close() ctx.response().setStatusCode(404).end() } } else { connection.close() ctx.fail(it.cause()) } } } else { ctx.fail(it.cause()) } }

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class RateMovie(val ctx:class RateMovie( val ctx: RoutingContext, val client: SQLClient, val movie: String, val rating: Int) { fun rate() { client.getConnection { if (it.succeeded()) { query(it.result()) } else { ctx.fail(it.cause()) } } } !!... } Divide and conquer strategy

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fun query(connection: SQLConnection) { val params = json { array(movie) } connection.queryWithParams("SELECT TITLE FROM MOVIE WHERE ID=?", params) { if (it.succeeded()) { val result = it.result() if (result.rows.size !== 1) { update(connection) } else { connection.close() ctx.response().setStatusCode(404).end() } } else { connection.close() ctx.fail(it.cause()) } } }

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fun update(connection: SQLConnection) { val params = json { array(rating, movie) } connection.updateWithParams("INSERT INTO RATING (VALUE, MOVIE_ID) VALUES ?, ?", params) { connection.close() if (it.succeeded()) { ctx.response().setStatusCode(201).end() } else { ctx.fail(it.cause()) } } }

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Going interactive with coroutines

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Toolkit approach Suspending lambdas and functions Sequential flow Coroutines can be composed Language control flow Kotlin Coroutines

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Suspend Begin End Resume Coroutine life cycle

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Coroutines are confined on Vert.x event loop thread awaitResult for asynchronous methods channel support integrates with coroutine ecosystem Coroutines for Vert.x

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launch(vertx.dispatcher()) { try { val result1 = awaitResult { handler !-> handler.handle(Future.succeededFuture("OK")) } println("Result 1 $result1") val result2 = awaitResult { handler !-> handler.handle(Future.failedFuture("Ouch")) } println("Result 2 $result1") } catch (e: Exception) { println("Ouch ${e.message}") } }

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launch(vertx.dispatcher()) { try { val result1 = awaitResult { handler !-> handler.handle(Future.succeededFuture("OK")) } println("Result 1 $result1") val result2 = awaitResult { handler !-> handler.handle(Future.failedFuture("Ouch")) } println("Result 2 $result1") } catch (e: Exception) { println("Ouch ${e.message}") } }

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launch(vertx.dispatcher()) { try { val result1 = awaitResult { handler !-> handler.handle(Future.succeededFuture("OK")) } println("Result 1 $result1") val result2 = awaitResult { handler !-> handler.handle(Future.failedFuture("Ouch")) } println("Result 2 $result1") } catch (e: Exception) { println("Ouch ${e.message}") } }

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launch(vertx.dispatcher()) { try { val result1 = awaitResult { handler !-> handler.handle(Future.succeededFuture("OK")) } println("Result 1 $result1") val result2 = awaitResult { handler !-> handler.handle(Future.failedFuture("Ouch")) } println("Result 2 $result1") } catch (e: Exception) { println("Ouch ${e.message}") } }

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launch(vertx.dispatcher()) { try { val result1 = awaitResult { handler !-> handler.handle(Future.succeededFuture("OK")) } println("Result 1 $result1") val result2 = awaitResult { handler !-> handler.handle(Future.failedFuture("Ouch")) } println("Result 2 $result1") } catch (e: Exception) { println("Ouch ${e.message}") } }

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launch(vertx.dispatcher()) { try { val result1 = awaitResult { handler !-> handler.handle(Future.succeededFuture("OK")) } println("Result 1 $result1") val result2 = awaitResult { handler !-> handler.handle(Future.failedFuture("Ouch")) } println("Result 2 $result1") } catch (e: Exception) { println("Ouch ${e.message}") } }

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launch(vertx.dispatcher()) { try { val result1 = awaitResult { handler !-> handler.handle(Future.succeededFuture("OK")) } println("Result 1 $result1") val result2 = awaitResult { handler !-> handler.handle(Future.failedFuture("Ouch")) } println("Result 2 $result1") } catch (e: Exception) { println("Ouch ${e.message}") } }

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launch(vertx.dispatcher()) { try { val result1 = awaitResult { handler !-> handler.handle(Future.succeededFuture("OK")) } println("Result 1 $result1") val result2 = awaitResult { handler !-> handler.handle(Future.failedFuture("Ouch")) } println("Result 2 $result1") } catch (e: Exception) { println("Ouch ${e.message}") } }

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launch(vertx.dispatcher()) { try { val result1 = awaitResult { handler !-> handler.handle(Future.succeededFuture("OK")) } println("Result 1 $result1") val result2 = awaitResult { handler !-> handler.handle(Future.failedFuture("Ouch")) } println("Result 2 $result1") } catch (e: Exception) { println("Ouch ${e.message}") } }

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launch(vertx.dispatcher()) { try { val result1 = awaitResult { handler !-> handler.handle(Future.succeededFuture("OK")) } println("Result 1 $result1") val result2 = awaitResult { handler !-> handler.handle(Future.failedFuture("Ouch")) } println("Result 2 $result1") } catch (e: Exception) { println("Ouch ${e.message}") } }

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launch(vertx.dispatcher()) { try { val result1 = awaitResult { handler !-> handler.handle(Future.succeededFuture("OK")) } println("Result 1 $result1") val result2 = awaitResult { handler !-> handler.handle(Future.failedFuture("Ouch")) } println("Result 2 $result1") } catch (e: Exception) { println("Ouch ${e.message}") } }

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(demo) “Going interactive with coroutines”

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Streaming with channels

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Streaming with channels Kotlin provides channels ReceiveChannel SendChannel Vert.x provides streams ReadStream WriteStream

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send(○) receive()

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vertx.createHttpServer().requestHandler { request !-> val readStream: ReadStream = request readStream.handler { buffer !-> !// Handle each buffer } readStream.exceptionHandler { err !-> request.response().setStatusCode(500).end("${err.message}") } readStream.endHandler { request.response().end("OK") } }.listen(8080) ɥ ReadStream

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vertx.createHttpServer().requestHandler { request !-> val readStream: ReadStream = request val receiveChannel: ReceiveChannel = readStream.toChannel(vertx) launch(vertx.dispatcher()) { try { for (buffer in receiveChannel) { !// Handle each buffer } request.response().end("OK") } catch (e: Exception) { request.response().setStatusCode(500).end("${e.message}") } } }.listen(8080) ɥ ReceiveChannel

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val writeStream: WriteStream = request.response() val item = Buffer.buffer("the-item") fun sendItemAndClose() { writeStream.write(item) request.response().end() } if (!writeStream.writeQueueFull()) { sendItemAndClose() } else { writeStream.drainHandler { sendItemAndClose() } } WriteStream ɣ

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val writeStream: WriteStream = request.response() val sendChannel = writeStream.toChannel(vertx) launch(vertx.dispatcher()) { sendChannel.send(Buffer.buffer("the-item")) request.response().end() } ɣ when full when drained SendChannel

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back-pressure

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Application Sockets HTTP WebSockets OS pipes DB cursors File system Apache Kafka IPC Vert.x

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Preemptive back-pressure try { while (true) { val amount = input.read(buffer) if (amount !== -1) { break } output.write(buffer, 0, amount) } } finally { output.close() } when buffer is full block the thread

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Cooperative back-pressure launch(vertx.dispatcher()) { try { while (true) { val buffer = input.receiveOrNull() if (buffer !== null) { break; } output.send(buffer); } } finally { output.close() } } when buffer is full suspends the coroutine

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Example - JSON parser Most parsers requires full buffering Process JSON as soon as possible Reduce the footprint Handle large JSON documents JSON streaming

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175 ops/ms 350 ops/ms 525 ops/ms 700 ops/ms Synchronous Coroutine 1 Coroutine (10 chunks) Vert.x parser Vert.x reactive parser Vert.x reactive parser (10 chunks)

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Coroutines vs RxJava

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Rxified application router { get("/movie/:id") { ctx !-> getMovie(ctx) } post("/rate/:id") { ctx !-> rateMovie(ctx) } get("/rating/:id") { ctx !-> getRating(ctx) } }

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val movie = ctx.pathParam("id") val rating = ctx.queryParam("getRating")[0] val query = "SELECT TITLE FROM MOVIE WHERE ID=?" val queryParams = json { array(movie) } val update = "INSERT INTO RATING (VALUE, MOVIE_ID) VALUES ?, ?" val updateParams = json { array(rating, movie) } val single = client.rxGetConnection().flatMap { connection !-> connection .rxQueryWithParams(query, queryParams) .flatMap { result !-> if (result.results.size !== 1) { connection.rxUpdateWithParams(update, updateParams) } else { Single.error(NotFoundException()) } } .doAfterTerminate { connection.close() } }

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val movie = ctx.pathParam("id") val rating = ctx.queryParam("getRating")[0] val query = "SELECT TITLE FROM MOVIE WHERE ID=?" val queryParams = json { array(movie) } val update = "INSERT INTO RATING (VALUE, MOVIE_ID) VALUES ?, ?" val updateParams = json { array(rating, movie) } val single = client.rxGetConnection().flatMap { connection !-> connection .rxQueryWithParams(query, queryParams) .flatMap { result !-> if (result.results.size !== 1) { connection.rxUpdateWithParams(update, updateParams) } else { Single.error(NotFoundException()) } } .doAfterTerminate { connection.close() } }

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val movie = ctx.pathParam("id") val rating = ctx.queryParam("getRating")[0] val query = "SELECT TITLE FROM MOVIE WHERE ID=?" val queryParams = json { array(movie) } val update = "INSERT INTO RATING (VALUE, MOVIE_ID) VALUES ?, ?" val updateParams = json { array(rating, movie) } val single = client.rxGetConnection().flatMap { connection !-> connection .rxQueryWithParams(query, queryParams) .flatMap { result !-> if (result.results.size !== 1) { connection.rxUpdateWithParams(update, updateParams) } else { Single.error(NotFoundException()) } } .doAfterTerminate { connection.close() } }

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val movie = ctx.pathParam("id") val rating = ctx.queryParam("getRating")[0] val query = "SELECT TITLE FROM MOVIE WHERE ID=?" val queryParams = json { array(movie) } val update = "INSERT INTO RATING (VALUE, MOVIE_ID) VALUES ?, ?" val updateParams = json { array(rating, movie) } val single = client.rxGetConnection().flatMap { connection !-> connection .rxQueryWithParams(query, queryParams) .flatMap { result !-> if (result.results.size !== 1) { connection.rxUpdateWithParams(update, updateParams) } else { Single.error(NotFoundException()) } } .doAfterTerminate { connection.close() } }

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val movie = ctx.pathParam("id") val rating = ctx.queryParam("getRating")[0] val query = "SELECT TITLE FROM MOVIE WHERE ID=?" val queryParams = json { array(movie) } val update = "INSERT INTO RATING (VALUE, MOVIE_ID) VALUES ?, ?" val updateParams = json { array(rating, movie) } val single = client.rxGetConnection().flatMap { connection !-> connection .rxQueryWithParams(query, queryParams) .flatMap { result !-> if (result.results.size !== 1) { connection.rxUpdateWithParams(update, updateParams) } else { Single.error(NotFoundException()) } } .doAfterTerminate { connection.close() } }

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val movie = ctx.pathParam("id") val rating = ctx.queryParam("getRating")[0] val query = "SELECT TITLE FROM MOVIE WHERE ID=?" val queryParams = json { array(movie) } val update = "INSERT INTO RATING (VALUE, MOVIE_ID) VALUES ?, ?" val updateParams = json { array(rating, movie) } val single = client.rxGetConnection().flatMap { connection !-> connection .rxQueryWithParams(query, queryParams) .flatMap { result !-> if (result.results.size !== 1) { connection.rxUpdateWithParams(update, updateParams) } else { Single.error(NotFoundException()) } } .doAfterTerminate { connection.close() } }

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val movie = ctx.pathParam("id") val rating = ctx.queryParam("getRating")[0] val query = "SELECT TITLE FROM MOVIE WHERE ID=?" val queryParams = json { array(movie) } val update = "INSERT INTO RATING (VALUE, MOVIE_ID) VALUES ?, ?" val updateParams = json { array(rating, movie) } val single = client.rxGetConnection().flatMap { connection !-> connection .rxQueryWithParams(query, queryParams) .flatMap { result !-> if (result.results.size !== 1) { connection.rxUpdateWithParams(update, updateParams) } else { Single.error(NotFoundException()) } } .doAfterTerminate { connection.close() } }

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val consumer = createKafkaConsumer(vertx, map, String!::class, JsonObject!::class) val stream = consumer.toObservable() stream .map({ record !-> record.value().getInteger("temperature") }) .buffer(1, TimeUnit.SECONDS) .map({ list !-> list.sum() }) .subscribe({ temperature !-> println("Current temperature is " + temperature) })

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Coroutines and RxJava Both are complementary Combine them with kotlinx-coroutines-rx1 kotlinx-coroutines-rx2

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TL;DR

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TL;DR ✓ Coroutines are great for workflows and correlated events ✓ Vert.x provides an unified end-to-end reactive model + ecosystem ✓ Make your Reactive applications Interactive in Kotlin

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Building Reactive Microservices in Java https:!//goo.gl/ep6yB9 Guide to async programming with Vert.x https:!//goo.gl/AcWW3A vertx.io ſ Kotlin Slack #vertx GitHub repo https:!//goo.gl/19BJiH