Scala Play Application for Production

開發時 activator run 啟動的是 DEV mode，會一直檢查程式有沒有修改過，如果有修改，就會自動編譯並 reload，但這個功能會增加 overhead，在 PROD mode 就不需要了。另外 PROD 環境產生的 error page，也不需要像 DEV mode 一樣有太多錯誤的細節。

Production 相關設定

Play 需要一個 secret key 用來對 session cookie 簽章，還有內建的加密 utilities。

application.conf

play.crypto.secret = "newsecret"

該密碼預設為 "changeme"，如果沒有修改這個密碼，在 PROD mode 就會發生錯誤，但在 DEV mode 就沒有檢查。

---

如果想要在 DEV 跟 PROD mode 使用不同的設定檔，可以在 conf 目錄中增加一個 prod-application.conf 新的設定檔，在啟動 PROD mode 時，加上設定檔的附加參數。

準備一個新的 prod-application.conf，內容為

include "application.conf"

play.crypto.secret = "newsecret"

另外同時準備一個 prod-logback.xml，新的 logback 設定檔，將 slick db sql statement 的 log 隱藏掉。

---

修改 build.sbt ，增加 JavaServerAppPackaging plugin，以及一些 production package 的設定

lazy val root = (project in file(".")).enablePlugins(PlayScala, JavaServerAppPackaging)

// production settings
maintainer := "charley <charley@maxkit.com.tw>"
packageSummary := "Play Slick Sample"
packageDescription := """A fun package description of our software,
  with multiple lines."""

// RPM SETTINGS
rpmVendor := "maxkit"
//rpmLicense := Some("BSD")
rpmChangelogFile := Some("changelog.txt")

---

Play 預設是使用 Netty，Netty 提供了一些參數可以調整，我們可以在 application.conf 中，調整這些參數。

play.server {

  # The server provider class name
  provider = "play.core.server.NettyServerProvider"

  netty {

    # The number of event loop threads. 0 means let Netty decide, which by default will select 2 times the number of
    # available processors.
    eventLoopThreads = 0

    # The maximum length of the initial line. This effectively restricts the maximum length of a URL that the server will
    # accept, the initial line consists of the method (3-7 characters), the URL, and the HTTP version (8 characters),
    # including typical whitespace, the maximum URL length will be this number - 18.
    maxInitialLineLength = 4096

    # The maximum length of the HTTP headers. The most common effect of this is a restriction in cookie length, including
    # number of cookies and size of cookie values.
    maxHeaderSize = 8192

    # The maximum length of body bytes that Netty will read into memory at a time.
    # This is used in many ways.  Note that this setting has no relation to HTTP chunked transfer encoding - Netty will
    # read "chunks", that is, byte buffers worth of content at a time and pass it to Play, regardless of whether the body
    # is using HTTP chunked transfer encoding.  A single HTTP chunk could span multiple Netty chunks if it exceeds this.
    # A body that is not HTTP chunked will span multiple Netty chunks if it exceeds this or if no content length is
    # specified. This only controls the maximum length of the Netty chunk byte buffers.
    maxChunkSize = 8192

    # Whether the Netty wire should be logged
    log.wire = false

    # The transport to use, either jdk or native.
    # Native socket transport has higher performance and produces less garbage but are only available on linux 
    transport = "jdk"

    # Netty options. Possible keys here are defined by:
    #
    # http://netty.io/4.0/api/io/netty/channel/ChannelOption.html
    #
    # Options that pertain to the listening server socket are defined at the top level, options for the sockets associated
    # with received client connections are prefixed with child.*
    option {

      # Set the size of the backlog of TCP connections.  The default and exact meaning of this parameter is JDK specific.
      # SO_BACKLOG = 100

      child {
        # Set whether connections should use TCP keep alive
        # SO_KEEPALIVE = false

        # Set whether the TCP no delay flag is set
        # TCP_NODELAY = false
      }

    }

  }
}

activator 常用指令

ex: activator clean

• clean: 刪除 target 目錄中的編譯結果
• update: 下載的 libraries
• compile: 編譯專案，產生到 target 目錄中
• eclipse: 產生 eclipse 專案 project file，使用前要先執行 compile
• run: 啟動 project，也可以用 activator "run 8888" 啟動到 TCP Port 8888
• publish: 產生專案的 jar，發佈到 build.sbt 中設定的 repository
• publish-local: 發佈到本機的 repository/local 目錄
• stage: 產生 production 專案的 script，通常放在 target/universal/stage 目錄中

產生 stage project

activator stage

完整地產生新的 stage project 要執行

activator clean update compile stage

產生 production project tar.gz file

activator universal:packageZipTarball

PROD mode

以下兩種方式可以啟動 Production Mode

-Dconfig.resource 的部分，會在 class path 尋找設定檔
-Dconfig.file 則是依照 file system 尋找設定檔

-J-Xms512M -J-Xmx1G -J-server 這幾個是啟動 application 的 JVM 參數

target/universal/stage/bin/test6 -Dconfig.resource=prod-application.conf -Dlogger.resource=prod-logback.xml -Dhttp.port=9000 -J-Xms512M -J-Xmx1G -J-server

target/universal/stage/bin/test6 -Dconfig.file=conf/prod-application.conf -Dlogger.file=conf/prod-logback.xml -Dhttp.port=9000 -J-Xms512M -J-Xmx1G -J-server

啟動後，會在 target/universal/stage/RUNNING_PID 產生 process ID 的檔案

如果希望在背景執行 application，就要搭配 nohup 啟動 server

nohup target/universal/stage/bin/test6 -Dconfig.resource=prod-application.conf -Dlogger.resource=prod-logback.xml -Dhttp.port=9000 -J-Xms512M -J-Xmx1G -J-server < /dev/null > /dev/null 2>&1 &

可以用 kill 的方式關掉背景執行的 server

kill -SIGTERM `cat target/universal/stage/RUNNING_PID`

kill -SIGKILL `cat target/universal/stage/RUNNING_PID`

start.sh stop.sh scripts

為了方便，我們把上面的啟動方式，做成一個 script，放在 conf 目錄中，這樣就會在 activator stage 時，同時複製到 target/universal/stage

conf/start.sh

#!/bin/bash

#export JAVA_OPTS=""
#export JAVA_OPTS="$JAVA_OPTS -Xms512M -Xmx1G -server"

console() {
    target/universal/stage/bin/test6 -Dconfig.resource=prod-application.conf -Dlogger.resource=prod-logback.xml -Dhttp.port=9000 -J-Xms512M -J-Xmx1G -J-server
}

server() {
    nohup target/universal/stage/bin/test6 -Dconfig.resource=prod-application.conf -Dlogger.resource=prod-logback.xml -Dhttp.port=9000 -J-Xms512M -J-Xmx1G -J-server < /dev/null > /dev/null 2>&1 &
}

case "$1" in

console)
    console
;;
server)
    server
;;
*)
    echo "Usage: $0 {console|server}"
;;
esac

exit 0

conf/stop.sh

#!/bin/bash

kill -SIGTERM `cat target/universal/stage/RUNNING_PID`

# kill -SIGKILL `cat target/universal/stage/RUNNING_PID`

然後就能用這樣的方式，啟動或停止 server

target/universal/stage/conf/start.sh server
target/universal/stage/conf/stop.sh

SSL

如果要讓 server 可以支援 HTTPS，我們需要做以下設定

Property	Purpose	Default Value
https.port	https port number
https.keyStore	儲存 private key 及 certificate 的檔案路徑
https.keyStoreType	key store type	JavaKeyStore(JKS)
https.keyStorePassword	password	blank password
https.keyStoreAlgorithm	key store algorithm	platform's default algorithm

也可以自己實作 SSLEngine，參考 Configuring HTTPS，製作新的 class CustomSSLEngineProvider(appProvider: ApplicationProvider) extends SSLEngineProvider 。

References

Mastering Play Framework for Scala

The Application Secret

第三章 : Play建置部署與常用指令

overriding-configuration

Start and stop a Scala application in production

Websocket in Scala Play

Websocket 就是在網頁 http protocol 之下，再增加的一層封裝協定，目的是讓 client 建立長時間的 socket 連線，在不重新建立連線的狀況下，我們可以傳送更多即時的資訊。

根據 WebSockets 的官方文件說明，scala play 2.5版已經調整為使用 Akka Streams 及 actors 來處理 WebSockets。

以最基本的 String 資料格式為例，跟一般的 http Action 一樣，websocket 也是以 Controller 為入口點。

WebSocketController 有兩個部分，index 是回傳一個簡單的 websocket 網頁 client，而 socket 就是主要處理 websocket 的部分。

// WebSocketController.scala
import play.api.mvc._
import play.api.libs.streams._

class WebSocketController @Inject()(implicit system: ActorSystem, materializer: Materializer) extends Controller {

  def index = Action { implicit request =>
    Ok(views.html.ws())
  }

  def socket = WebSocket.accept[String, String] { request =>
    ActorFlow.actorRef(out => MyWebSocketActor.props(out))
  }
}

ActorFlow.actorRef(...) 可以被替代為 Akka Streams Flow[In, Out, _]，但還是用 actors 撰寫會比較直接。

在 WebSocketController.scala 的下面，我們直接將處理 websocket 的 MyWebSocketActor 寫在下面，收到字串就會直接回傳 echo String: 加上原本收到的字串。

import akka.actor._

object MyWebSocketActor {
  def props(out: ActorRef) = Props(new MyWebSocketActor(out))
}

class MyWebSocketActor(out: ActorRef) extends Actor {
  def receive = {
    case msg: String =>
      Logger.debug(s"echo String: ${msg}")
      out ! s"echo String: ${msg}"
  }
}

在 routes 加上兩個 service uri

GET         /ws                                         controllers.WebSocketController.socket
GET         /wstest                                     controllers.WebSocketController.index

如果不要自己撰寫 websocket client 網頁，可以直接用 Websocket Echo Test 測試，把 Location: wss://echo.websocket.org 改為 ws://localhost:9000/ws，Use secure WebSocket (TLS) 取消勾選。點 Connect 以後，就可以對 ws server 發送文字訊息。

以下是自己撰寫 websocket 網頁的 sample: ws.scala.html

<!DOCTYPE html>
<meta charset="utf-8" />
<title>WebSocket Test</title>
<script language="javascript" type="text/javascript">
    //var wsUri = "ws://localhost:9000/ws";
    //var output;

    function init()
    {
        //output = document.getElementById("output");
        //testWebSocket();
    }

    function testWebSocket()
    {
        var wsUri= document.getElementById('wsUri').value;
        websocket = new WebSocket(wsUri);
        //websocket.binaryType = 'arraybuffer';

        websocket.onopen = function(evt) { onOpen(evt) };
        websocket.onclose = function(evt) { onClose(evt) };
        websocket.onmessage = function(evt) { onMessage(evt) };
        websocket.onerror = function(evt) { onError(evt) };
    }

    function closeWebSocket() {
        websocket.close();
    }

    function onOpen(evt)
    {
        writeToScreen("CONNECTED");
        //doSend("WebSocket rocks");
    }

    function onClose(evt)
    {
        writeToScreen("DISCONNECTED");
    }

    function onMessage(evt)
    {
        console.log(evt);

        if ( evt.data instanceof ArrayBuffer ) {
            console.log( evt.data );
        } else {
            writeToScreen('<span style="color: blue;">RESPONSE: ' + evt.data+'</span>');
        }
        //websocket.close();
    }

    function onError(evt)
    {
        writeToScreen('<span style="color: red;">ERROR:</span> ' + evt.data);
    }

//    function doSend(message)
//    {
//        writeToScreen("SENT: " + message);
//        websocket.send(message);
//    }

    function doSendInput()
    {
        var message= document.getElementById('sendMessage').value;

        writeToScreen("SENT: " + message);
        websocket.send( message );
        //websocket.send( JSON.stringify(JSON.parse(message)) );
        //var byteArray = new Uint8Array(message);
        //websocket.send( byteArray.buffer );
    }

    function writeToScreen(message)
    {
        var pre = document.createElement("p");
        pre.style.wordWrap = "break-word";
        pre.innerHTML = message;

        output = document.getElementById("output");
        output.appendChild(pre);
    }

    function clearScreen()
    {
        var nodes = document.getElementById("output");
        while (nodes.hasChildNodes()) {
            nodes.removeChild(nodes.childNodes[0]);
        }
    }

    window.addEventListener("load", init, false);

    </script>

<h2>WebSocket Test</h2>

<input id="wsUri" size="35" value="ws://localhost:9000/ws"></input>

<button id="close" onclick="javascipt:testWebSocket()">connect</button>
<button id="close" onclick="javascipt:closeWebSocket()">close</button>

<br/><br/>

<input id="sendMessage" size="35" value="測試 WebSocket!!!"></input>
<button id="send" onclick="javascipt:doSendInput()">Send</button>
<button id="clear" onclick="javascipt:clearScreen()">clear</button>
<div id="output"></div>

啟動 server 瀏覽網頁 http://localhost:9000/wstest 就可以測試 websocket

如果要將資料的格式換成 json，就稍微調整一下程式。

//WebSocketController.scala 把 String 換成 JsValue

  def socketJs = WebSocket.accept[JsValue, JsValue] { request =>
    ActorFlow.actorRef(out => MyWebSocketActor.props(out))
  }

// 接收的資料改為 JsValue，並直接回傳原始的 json
class MyWebSocketActor(out: ActorRef) extends Actor {
  def receive = {
    case msg: JsValue =>
      Logger.debug(s"echo JsValue: ${msg}")
      out ! msg
  }
}

routes 修改為 socketJs method

GET         /ws                                         controllers.WebSocketController.socketJs
GET         /wstest                                     controllers.WebSocketController.index

ws.scala.html 中發送資料的部分，以 JSON.parse 及 JSON.stringify 確認發送的資料是 json。

    function doSendInput()
    {
        var message= document.getElementById('sendMessage').value;

        writeToScreen("SENT: " + message);
        //websocket.send( message );
        websocket.send( JSON.stringify(JSON.parse(message)) );
    }

測試的字串要改為 json

References

Binary websockets with Play 2.0 and Scala (and a bit op JavaCV/OpenCV)

Handling data streams reactively

Akka Streams integration in Play Framework 2.5

How to use XML in scala

scala 內建了 scala.xml 可以處理 XML，以下我們簡單測試了一下 xml 的功能，目前看起來，標準函式庫的功能就足夠應用的需求了。

產生及使用 scala.xml

scala 可以直接偵測 < 這個符號，並以 xml 的方式處理，在程式中，直接把 xml指定給變數，就會直接產生 xml 物件。

scala> val xml = <store><item type="book">Novel</item><item type="pen">pencil</item></store>
xml: scala.xml.Elem = <store><item type="book">Novel</item><item type="pen">pencil</item></store>

產生 xml 物件後，可以用 text method，將所有欄位的 value 全部印出來

scala> xml.text
res0: String = Novelpencil

用 XPath 的語法，可以取得子節點的內容

scala> xml\"item"
res1: scala.xml.NodeSeq = NodeSeq(<item type="book">Novel</item>, <item type="pen">pencil</item>)

scala> (xml\"item").map(_.text).mkString(" ")
res2: String = Novel pencil

用 "@type" selector，可以取得所有 type 屬性的值

scala> (xml\"item").map(_\"@type")
res3: scala.collection.immutable.Seq[scala.xml.NodeSeq] = List(book, pen)

"@type" 只能取得目前這個節點的 children，如果要將所有出現同樣屬性的節點都取出來，就要用 "\" selector

scala> znodes\"z"
res5: scala.xml.NodeSeq = NodeSeq(<z x="1"/>)

scala> znodes\\"z"
res6: scala.xml.NodeSeq = NodeSeq(<z x="1"/>, <z x="2"/>, <z x="3"/>, <z x="4"/>)

跟剛剛一樣的方法，就可以找到屬性 x 的所有 values

scala> (znodes\\"z").map(_\"@x")
res12: scala.collection.immutable.Seq[scala.xml.NodeSeq] = List(1, 2, 3, 4)

如果是一個 xml string，可以用 scala.xml.XML.loadString 將 string 轉換為 xml。

scala> val xmlstring = """<store><item type="book">Novel</item><item type="pen">pencil</item></store>"""
xmlstring: String = <store><item type="book">Novel</item><item type="pen">pencil</item></store>

scala> val xmlfromstring = scala.xml.XML.loadString(xmlstring)
xml: scala.xml.Elem = <store><item type="book">Novel</item><item type="pen">pencil</item></store>

scala> xml == xmlfromstring
res13: Boolean = true

manual Serializing and Deserializing xml

首先定義 Stock class，在 toXml method 中，可以直接用 {symbol} 將 Stock 物件中的資料，產生到 xml 中，而 fromXml 就是用剛剛的 text 的方式取得 xml 裡面的資料放入 Stock 物件中。

case class Stock(var symbol: String, var businessName: String, var price: Double) {

  // convert Stock fields to XML
  def toXml = {
    <stock>
      <symbol>{symbol}</symbol>
      <businessName>{businessName}</businessName>
      <price>{price}</price>
    </stock>
  }

  override def toString =
    s"symbol: $symbol, businessName: $businessName, price: $price"

}

object Stock {

  // convert XML to a Stock
  def fromXml(node: scala.xml.Node):Stock = {
    val symbol = (node \ "symbol").text
    val businessName = (node \ "businessName").text
    val price = (node \ "price").text.toDouble
    new Stock(symbol, businessName, price)
  }
}

用個簡單的 TestXml 測試 toXml 及 fromXml

object TestXml extends App {

  // convert a Stock to its XML representation
  val aapl = new Stock("AAPL", "Apple", 600d)
  println(aapl.toXml)

  // convert an XML representation to a Stock
  val googXml = <stock>
    <symbol>GOOG</symbol>
    <businessName>Google</businessName>
    <price>620.00</price>
  </stock>
  val goog = Stock.fromXml(googXml)
  println(goog)
}

執行結果如下

<stock>
      <symbol>AAPL</symbol>
      <businessName>Apple</businessName>
      <price>600.0</price>
    </stock>

symbol: GOOG, businessName: Google, price: 620.0

References

Basic XML processing with Scala

Practical Scala – processing XML

Serializing and deserializing XML in Scala

Generating dynamic XML from Scala source code (like a template)

Play JSON library

Scala Play 支援自己實作的 play.api.libs.json JSON Lirary

類別

• JsValue: trait 代表任意一種 JSON value，以下這些是 extend JsValue 的 case classes

1. JsString
2. JsNumber
3. JsBoolean
4. JsObject
5. JsArray

6. JsNull

• Json
  提供 utilties，轉換 JsValue

• JsPath
  代表 JsValue 資料結構中的 path，類似 XML 的 XPath，可使用 pattern 在 JsValue 中進行 data traversal

Converting to a JsValue

• 以 json String 直接 parsing 並轉換

import play.api.libs.json._

val json: JsValue = Json.parse("""
{
  "name" : "Watership Down",
  "location" : {
    "lat" : 51.235685,
    "long" : -1.309197
  },
  "residents" : [ {
    "name" : "Fiver",
    "age" : 4,
    "role" : null
  }, {
    "name" : "Bigwig",
    "age" : 6,
    "role" : "Owsla"
  } ]
}
""")

直接將上面的 code ，在 activator console 中進行測試，就可以得到測試結果

scala> json
res0: play.api.libs.json.JsValue = {"name":"Watership Down","location":{"lat":51.235685,"long":-1.309197},"residents":[{"name":"Fiver","age":4,"role":null},{"name":"Bigwig","age":6,"role":"Owsla"}]}

• 以 class 的方式建立 JsValue

import play.api.libs.json._

val json: JsValue = JsObject(Seq(
  "name" -> JsString("Watership Down"),
  "location" -> JsObject(Seq("lat" -> JsNumber(51.235685), "long" -> JsNumber(-1.309197))),
  "residents" -> JsArray(Seq(
    JsObject(Seq(
      "name" -> JsString("Fiver"),
      "age" -> JsNumber(4),
      "role" -> JsNull
    )),
    JsObject(Seq(
      "name" -> JsString("Bigwig"),
      "age" -> JsNumber(6),
      "role" -> JsString("Owsla")
    ))
  ))
))

使用 Writes converters

scala converting to a JsValue 是以 Json.toJsonT(implicit writes: Writes[T]) 進行轉換的，這需要 Writes 物件的幫忙。Play JSON API 提供了一個 implicit Writes 物件，可以轉換 Int, Double, String, Boolean ...，同時也支援 collections

import play.api.libs.json._

// basic types
val jsonString = Json.toJson("Fiver")
val jsonNumber = Json.toJson(4)
val jsonBoolean = Json.toJson(false)

// collections of basic types
val jsonArrayOfInts = Json.toJson(Seq(1, 2, 3, 4))
val jsonArrayOfStrings = Json.toJson(List("Fiver", "Bigwig"))

如果要轉換自己的資料物件類別，就須要提供一個 implicit Writes converter

case class Location(lat: Double, long: Double)
case class Resident(name: String, age: Int, role: Option[String])
case class Place(name: String, location: Location, residents: Seq[Resident])

import play.api.libs.json._

implicit val locationWrites = new Writes[Location] {
  def writes(location: Location) = Json.obj(
    "lat" -> location.lat,
    "long" -> location.long
  )
}

implicit val residentWrites = new Writes[Resident] {
  def writes(resident: Resident) = Json.obj(
    "name" -> resident.name,
    "age" -> resident.age,
    "role" -> resident.role
  )
}

implicit val placeWrites = new Writes[Place] {
  def writes(place: Place) = Json.obj(
    "name" -> place.name,
    "location" -> place.location,
    "residents" -> place.residents)
}

val place = Place(
  "Watership Down",
  Location(51.235685, -1.309197),
  Seq(
    Resident("Fiver", 4, None),
    Resident("Bigwig", 6, Some("Owsla"))
  )
)

val json = Json.toJson(place)

也可以使用 combinator pattern

import play.api.libs.json._
import play.api.libs.functional.syntax._

implicit val locationWrites: Writes[Location] = (
  (JsPath \ "lat").write[Double] and
  (JsPath \ "long").write[Double]
)(unlift(Location.unapply))

implicit val residentWrites: Writes[Resident] = (
  (JsPath \ "name").write[String] and
  (JsPath \ "age").write[Int] and
  (JsPath \ "role").writeNullable[String]
)(unlift(Resident.unapply))

implicit val placeWrites: Writes[Place] = (
  (JsPath \ "name").write[String] and
  (JsPath \ "location").write[Location] and
  (JsPath \ "residents").write[Seq[Resident]]
)(unlift(Place.unapply))

Traversing a JsValue structure

可以 traverse JsValue 並取得特定的資料欄位，這就類似 Scala XML processing

• Simple Path \

val lat = (json \ "location" \ "lat").get
// returns JsNumber(51.235685)

• Recursive path \

val names = json \\ "name"
// returns Seq(JsString("Watership Down"), JsString("Fiver"), JsString("Bigwig"))

• Index lookup (針對 JsArrays)

val bigwig = (json \ "residents")(1)
// returns {"name":"Bigwig","age":6,"role":"Owsla"}

Converting from a JsValue

• 使用 String utilities

val minifiedString: String = Json.stringify(json)

適合閱讀的格式

val readableString: String = Json.prettyPrint(json)

• 使用 JsValue.as/asOpt

將 JsValue 轉換為其他資料類別的方式，最簡單的方式就是用 JsValue.asT: T ，但這個方式需要用到一個 implicit converter: Reads[T]

val name = (json \ "name").as[String]
// "Watership Down"

val names = (json \\ "name").map(_.as[String])
// Seq("Watership Down", "Fiver", "Bigwig")

但是 as 可能會產生 JsResultException，所以比較好的方式，應該是改用 JsValue.asOptT: Option[T]

val nameOption = (json \ "name").asOpt[String]
// Some("Watership Down")

val bogusOption = (json \ "bogus").asOpt[String]
// None

• 使用 validation

會產生兩種 JsResult

1. JsSuccess: validation/convertion 成功
2. JsError: validation/conversion 失敗

val json = { ... }

val nameResult: JsResult[String] = (json \ "name").validate[String]

// Pattern matching
nameResult match {
  case s: JsSuccess[String] => println("Name: " + s.get)
  case e: JsError => println("Errors: " + JsError.toJson(e).toString())
}

// Fallback value
val nameOrFallback = nameResult.getOrElse("Undefined")

// map
val nameUpperResult: JsResult[String] = nameResult.map(_.toUpperCase())

// fold
val nameOption: Option[String] = nameResult.fold(
  invalid = {
    fieldErrors => fieldErrors.foreach(x => {
      println("field: " + x._1 + ", errors: " + x._2)
    })
    None
  },
  valid = {
    name => Some(name)
  }
)

• JsValue 轉換成 data model

case class Location(lat: Double, long: Double)
case class Resident(name: String, age: Int, role: Option[String])
case class Place(name: String, location: Location, residents: Seq[Resident])

import play.api.libs.json._
import play.api.libs.functional.syntax._

implicit val locationReads: Reads[Location] = (
  (JsPath \ "lat").read[Double] and
  (JsPath \ "long").read[Double]
)(Location.apply _)

implicit val residentReads: Reads[Resident] = (
  (JsPath \ "name").read[String] and
  (JsPath \ "age").read[Int] and
  (JsPath \ "role").readNullable[String]
)(Resident.apply _)

implicit val placeReads: Reads[Place] = (
  (JsPath \ "name").read[String] and
  (JsPath \ "location").read[Location] and
  (JsPath \ "residents").read[Seq[Resident]]
)(Place.apply _)


val json = { ... }

val placeResult: JsResult[Place] = json.validate[Place]
// JsSuccess(Place(...),)

val residentResult: JsResult[Resident] = (json \ "residents")(1).validate[Resident]
// JsSuccess(Resident(Bigwig,6,Some(Owsla)),)

Reference

Scala Json in Play

JSON_basics