Developing Java EE 7 Applications with

Scala (CON2664) Demystifying the Object-Functional

Peter Pilgrim Scala and Java EE

Independent contractor

@peter_pilgrim  

Xenonique

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About Me •  Scala and Java EE developer independent

contractor •  Digital transformation / e-commerce •  Java Champion •  Working on the JVM since 1998

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Java EE 7 Developer Handbook September  2013  Packt  Publishing    Digital Java EE 7 Web APPS December  2014  

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Agenda •  Scala Technology •  Java EE 7 •  CDI •  JSF, Servlets •  JAX-RS, JMS

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#1 Scala Object-functional Since 2003 Statically typed programming Scalable Language Inventor: Professor Martin Odersky, EPFL, Typesafe

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#1 Scala Pattern Matching Case Classes Traits, Mix-ins, Collections Expressions, In-fix operators Functions, Closures, Control Abstractions Extension through Library functions

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#1 Scala Gradle, Gradle, Gradle v2.0 Groovy assembler, builder Comprehensible, Configurable, Flexible Works with Scala since Gradle v1.7 With Gradle, building WAR files is very straightforward

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Scala Language

var age: Int = 37 val pi: Double = 3.141596527 val text: String = "human nature" val r = if (age >= 18 ) "Adult" else "Child"

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Scala Test #1

import collection.mutable.Stack import org.scalatest._ import org.scalatest.junit.JUnitRunner @RunWith(classOf[JUnitRunner]) class StackSpec extends FlatSpec with Matchers { /* ... */

}

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Scala Test #2

class StackSpec extends FlatSpec with Matchers { "A Stack" should "pop values in last-in-first-out order" in { val stack = new Stack[Int] stack.push(1) stack.push(2) stack.pop() should be (2) stack.pop() should be (1) } /* ... */ }

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Scala Test #3

class StackSpec extends FlatSpec with Matchers { /* ... */ it should "throw NoSuchElementException if an empty stack is popped" in { val emptyStack = new Stack[Int] a [NoSuchElementException] should be thrownBy {

emptyStack.pop() } } }

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Java EE 7 released 2013 Built products on top of a standard platform Transactions, Concurrency, Remote Endpoints, Lifecycle, State, Persistence

Java is a programming language. Java is a virtual machine. Java is a platform.

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Java  EE  7  

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Context & Dependency Injection

•  Writing Scala beans •  Annotate with Scala @BeanProperty on

POSI (Plain Old Scala Instances) •  Ensure compatibility with Java code •  @BeanProperty exposes properties to CDI

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Plain Old Scala Instance

@ApplicationScoped class CashierService { @BeanProperty @Inject() var service: PaymentService = _ def process( acc: Account, amount: BigDecimal): Unit = { service.debit(amount); acc.balance = acc.balance - amount } }

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CDI Dependent Object

@ApplicationScoped class PaymentService { var message: String = _ def debit(amount: BigDecimal): Unit = { message = s"You paid ${amount}" } } // Note String interpolators

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CDI Model instance

class Account( var balance: BigDecimal ) // This is a complete class definition! ;-)

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CDI Scala Gotchas •  Companion Objects cannot be used •  Case Classes (and obviously Case Objects) – Failure due to creation of multiple static methods

in byte code

•  Implicit class parameters •  Implicit method parameters •  Lazy public vals also fail

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Building Java EE 7 War Files •  Gradle allows developers to build WAR files

very easy and also add customisation •  Explicitly include the Scala Library JAR as a

dependency •  With SBT, it is harder to create WAR files – Battling between *.scala and *.sbt files

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Sample Gradle Dependencies

dependencies { providedCompile 'javax:javaee-api:7.0’ compile 'org.scala-lang:scala-library:2.11.2' testCompile 'junit:junit:4.11' testCompile 'org.scalatest:scalatest_2.11:2.2.0’ }

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CDI Factory #1

trait Maker { def createSample(): Fruit } @ApplicationScoped class FruitFactory { private class CocktailMaker extends Maker { override def createSample():Fruit = new Strawberry } private class FruitSaladMaker extends Maker { override def createSample():Fruit = new Banana } }

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CDI Factory #2

@ApplicationScoped class FruitFactory { // ... @Produces def generateCocktail(): Maker = new CocktailMaker() @Produces def generateFruitSalad(): Maker = new FruitSaladMaker() }

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CDI Factory #3

trait Fruit { val price: Double; val name = this.getClass.getSimpleName } case class Apple() extends Fruit { override val price = 0.75 } case class Banana() extends Fruit { override val price = 0.95 } case class Strawberry() extends Fruit { override val price = 2.99 }

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#1 Collection Of Case Classes

@ApplicationScoped class FruitVendor { def sell( fruit: Fruit with Product with Serializable, quantity: Int): Double = { fruit.price * quantity } }

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#2 Collection Of Case Classes

@Test def shouldPriceFruitWithQuantity(): Unit = { val fruits = List((Apple,2), (Orange,4), (Banana,5)) for ( (fruit, quantity) <- fruits) { val product = fruitVendor.sell(fruit(), quantity) assertEquals( product, fruit().price * quantity, 0.01 ) } }

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#3 Collection Of Case Classes Sugaring of Supertype

scala> val list = List( Apple -> 1, Orange -> 4, Banana -> 7 ) list: List[(scala.runtime.AbstractFunction0[ Product with Serializable with Fruit] with Serializable, Int)] = List((Apple,1), (Orange,4), (Banana,7)) // [R]AbstractFunction0.apply() => R // fruit() returns the Fruit mix-in type

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#2 Arquillian: Prefer integration tests over unit tests. You can write Arquillian tests with Scala You cannot yet mix ScalaTest specifications

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Writing Arquillian Tests with Scala #1

// HERE WOULD BE THE IDEAL WORLD import org.jboss.arquillian.junit.Arquillian import org.junit.runner.RunWith import org.scalatest.junit. JUnitSuite} import org.scalatest.{FlatSpecLike, Matcher} @RunWith(classOf[Arquillian], classOf[JUnitRunner]) /* ;-) */ class HelloArquillianSpec extends JUnitSuite with FlatSpecLike with Matchers { }

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Writing Arquillian Tests with Scala #2

// The Reality of the Situation in 2014 @RunWith(classOf[Arquillian]) class HelloArquillianSpec extends JUnitSuite with Matchers { // You can’t use BDD like specificationsL }

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Writing Arquillian Tests with Scala #3

// Add a companion object, generate a WAR file object HelloArquillianSpec { @Deployment def createDeployment():WebArchive = { ShrinkWrap.create( classOf[WebArchive], "test.war") .addPackage("uk.co.xenonique.digitalone") .addAsLibrary( GradleDependency.resolve(

"org.scala-lang:scala-library:2.11.1") ) .addAsLibrary( GradleDependency.resolve(

"org.scalatest:scalatest_2.11:2.2.0") ) .addAsManifestResource(EmptyAsset.INSTANCE, "beans.xml”) } }

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Writing Arquillian Tests with Scala #4

// Add a companion object @RunWith(classOf[Arquillian]) class HelloArquillianSpec extends JUnitSuite with Matchers { @Inject var hello: Hello = _ @Test def shouldPrintAPoliteGreeting():Unit = { val msg = hello.hello("JavaOne 2014") // ;-) At least, we can use matchers! (msg) should be ("Hello JavaOne 2014") } }

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#3  Servlets  A  Java  Servlet  is  a  web  component  managed  container.  Java  Servlets  are  based  on  the  Java  technology,  they  generate  dynamic  content,  and  hence  the  container  that  manages  them  is  capable  of  delivering  dynamic  content  to  the  web  client.    

 

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Simplest Json Servlet @WebServlet(Array("/simple")) class SimpleServlet extends HttpServlet { override def doGet(req: HttpServletRequest, resp: HttpServletResponse): Unit = { resp.setContentType("application/json”) val writer = resp.getWriter() writer.println( s""" |{ | "trackTitle": "Two Tribes", | "class": "${this.getClass().getName}", | "date": "${new Date()}" |} """.stripMargin ) } }

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#4 JAX-RS Easy to write in Scala Jackson Annotations, Json4S We demand Json support with seamless Scala support Jackson, especially, FasterXML is extremely helpful https://github.com/FasterXML/jackson-annotations/ For Parsing JSON from text strings, then examine Json4S https://github.com/json4s/json4s

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Convert Posis to Json

// How do we convert this POSI to JSON // to seamlessly and easily? ;-/ class Traveller( @BeanProperty var givenName: String, @BeanProperty var familyName: String, @BeanProperty var dateOfBirth: Date , @BeanProperty var docNo: String )

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Jackson Json Jaxb Annotations

// Look at the Jackson JAX-B project for // inspiration ;-D class Traveller2( @BeanProperty @JsonProperty("givenName") var givenName: String, @BeanProperty @JsonProperty("familyName") var familyName: String, @BeanProperty @JsonProperty("dateOfBirth") var dateOfBirth: Date, @BeanProperty @JsonProperty("documentNo") var docNo: String )

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Restful Scala JAX-RS Service Endpoint

@Path("/traveller") class TravellerServiceEndpoint { @GET() @Produces(Array(MediaType.APPLICATION_JSON)) def retrieve(): Response = { val cal = Calendar.getInstance() cal.set(1986, Calendar.MAY, 21) val dob = cal.getTime val traveller = new Traveller2("Sam", "Smith", dob, "1234567890") Response.ok(traveller).build() } }

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Jackson Json Mapping With Provider

@Singleton @Provider @Consumes(Array(MediaType.APPLICATION_JSON, "application/*+json", "text/json")) @Produces(Array(MediaType.APPLICATION_JSON, "application/*+json", "text/json")) class JacksonScalaContextResolver extends JacksonJaxbJsonProvider(JacksonScalaContextResolver.getObjectMapper, JacksonJaxbJsonProvider.DEFAULT_ANNOTATIONS) object JacksonScalaContextResolver { def getObjectMapper: ObjectMapper = { val mapper = new ObjectMapper with ScalaObjectMapper mapper.registerModule(new DefaultScalaModule) mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false) mapper.setSerializationInclusion(Include.NON_NULL) mapper } }

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Case Classes Instances and Jackson Annotations

@JsonIgnoreProperties(Array("databaseId", "computedDeliveryDateTime")) case class Traveller3( @BeanProperty @JsonProperty("givenName") var givenName: String, @BeanProperty @JsonProperty("familyName") var familyName: String, @BeanProperty @JsonProperty("dateOfBirth") var dateOfBirth: Date , @BeanProperty @JsonProperty("documentNo") var docNo: Option[String], @BeanProperty var computedDeliveryDateTime: Date = new Date())

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Consuming of Json to Scala Case Class Instance #1

@POST() @Consumes(Array(MediaType.APPLICATION_JSON)) def store( traveller: Traveller3): Response = { if ( traveller.getDocNo().isEmpty ) { Response.status( Response.Status.BAD_REQUEST) .entity(ErrorMessage("E199", "Missing document No")) .build() } else { Response.ok().build() } }

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Case Class #2

case class ErrorMessage( @JsonProperty("id") var id: String, @JsonProperty("error") var text: String) // Renders // { "id": "E199", // "error": "Missing document No" // }

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#5 JSF Easy to write in Scala Conversational, FlowScoped RequestScoped, SessionScoped All types of validation are supported including BeanValidation just like Java

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Conversational Scoped Managed Bean

@Named("wizard") @ConversationScoped class RegisterDrivingLicense extends Serializable { @Inject var conversation: Conversation = _; @BeanProperty var title: String = _ @BeanProperty var firstName: String = _ @BeanProperty var lastName: String = _ /* ... */ }

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Controller Methods

def jumpGettingStarted(): String = { beginConversation() "form1?faces-redirect=true" } def submitPage1(): String = { beginConversation() "form2?faces-redirect=true" }

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Conversational States

def beginConversation(): Unit = { if (conversation.isTransient()) { conversation.begin() } } def endConversation(): Unit = { if (!conversation.isTransient()) { conversation.end() } }

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Finish Conversational Scopes

def submitDeclarationPage(): String = { endConversation() if ( !declaration ) { // The declaration was not signed cancelApplication() } else { // Here the form is complete "end?faces-redirect=true" } }

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#6 JMS JMS is straight forward to code with Scala MDB is essentially an asynchronous EJB Tricky part is publishing with JMS 2.0!

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JMS with CDI Qualifiers #1

class JMSResourceProducer { @Resource(name = "jms/OrderConnectionFactory") val orderConnFactory: QueueConnectionFactory = _ @Produces @Order @Resource(name = "jms/OrderQueue") val orderQueue: Queue = _ @Produces @Order def createOrderConnection(): QueueConnection = orderConnectionFactory.createQueueConnection() /* ... */ }

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JMS with CDI Qualifiers #2

class JMSResourceProducer { /* ... */ @Produces @Order def createOrderSession( @Order conn:QueueConnection): QueueSession = conn.createQueueSession( true, Session.AUTO_ACKNOWLEDGE) }

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#Conclusion(1) Source code is available now! https://github.com/peterpilgrim/digital-scala-javaone-2014

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#Conclusion(2) Scala and Java EE 7 integrate well from an Object-Oriented point of view Java EE 8 and Lambda API promise a functional approach. Java EE 7 annotations work in Scala. The ability of Jackson annotations and a singleton provider to seamlessly handle Scala’s case classes is a wonderful addition. Arquillian almost works completely with ScalaTest.

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#Conclusion(3) WAR files require the runtime Scala Library Decent server configuration using Chef and Puppet can obviate the bundling of the runtime Scala allows developers to avoid Java boilerplate Library writers should prefer to explicitly declare the return types of functions and methods

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@peter_pilgrim  

uk.linkedin.com/in/peterpilgrim

2000/  

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#101 Bonus Information on Scala A Powerful weapon that requires great responsibility Great developers can create apps AM #1: “Interactions and individuals over processes and tools”

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How to avoid null pointers in Scala Programming?

val greeting1: Option[String] = Some("AOTB14") val greeting2: Option[String] = None

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Pattern Matching

def checker(p : Option[String]): String = { p match { case Some(v) => v case _ => "Unexpected" } } checker(greeting1) // "Hello AOTB14" checker(greeting2) // "Unspecified"

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Scala’s generic immutable list collection type

val list: List[Int] = List(1,2,3,4) list.foreach { x => println(x) } // 1,2,3,4

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Scala’s option behaves like collection type #2

greeting1.foreach { x => println(s"Work: ${x}" ) } // Work: Hello AOTB14

greeting2.foreach { x => println(s"Work: ${x}" ) } // *** nothing happens ***

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Read, Evaluate, Print, Loop •  Scala, Clojure, Groovy, Kotlin, Ceylon, Fantom All have a interpretative mode •  Java JDK does not (yet) have an official REPL (However try out javarepl.com online) •  Fingers crossed Project Kulla in JDK 9 http://blog.gmane.org/gmane.comp.java.openjdk.general

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