Scala tech talk

presentation of the Scala language for Java programmers

Transcript

1. Scala
2. Who am I?
3. Yann Simon @simon_yann
5. Why Scala?
6. Fear to lose job?
10. Java can be pain #1
11. public String createInvoiceName( Date invoiceDate, String invoiceId, String userId, String firmId, boolean directInvoice, boolean firmInvoice, boolean electronic) { // ...
12. String newInvoiceId = invoiceCreator.createInvoiceName( new Date(), "45AE-45F", "872346", "abc-234", true, false, false );
13. let's make it readable
14. String newInvoiceId = invoiceCreator.createInvoiceName( new Date(), // invoiceDate "45AE-45F", // invoiceId "872346", // userId "abc-234", // firmId true, // directInvoice false, // firmInvoice false // electronic );
15. OO maybe?
16. public class NewInvoiceNameCommand { private final Date invoiceDate; private final String invoiceId; private final String userId; private final String firmId; private final boolean directInvoice; private final boolean firmInvoice; private final boolean electronic; public NewInvoiceNameCommand( Date invoiceDate, String invoiceId, String userId, String firmId, boolean directInvoice, boolean firmInvoice, boolean electronic) { this.invoiceDate = invoiceDate; this.invoiceId = invoiceId; this.userId = userId; this.firmId = firmId; this.directInvoice = directInvoice; this.firmInvoice = firmInvoice; this.electronic = electronic; } public Date getInvoiceDate() { return invoiceDate; } public String getInvoiceId() { return invoiceId; } public String getUserId() { return userId; } public String getFirmId() { return firmId; } public boolean isDirectInvoice() { return directInvoice; } public boolean isFirmInvoice() { return firmInvoice; } public boolean isElectronic() { return electronic; } }
17. public String createInvoiceName( NewInvoiceNameCommand newInvoiceNameCommand) { // ... return "id"; } String newInvoiceId = invoiceCreator.createInvoiceName( newInvoiceNameCommand);
18. NewInvoiceNameCommand newInvoiceNameCommand = new NewInvoiceNameCommand( new Date(), "45AE-45F", "872346", "abc-234", true, false, false );
19. builder pattern to the rescue
20. public class NewInvoiceNameCommand { public static class NewInvoiceNameCommandBuilder { private Date invoiceDate; private String invoiceId; private String userId; private String firmId; private boolean directInvoice; private boolean firmInvoice; private boolean electronic; public NewInvoiceNameCommand build() { return new NewInvoiceNameCommand( invoiceDate, invoiceId, userId, firmId, directInvoice, firmInvoice, electronic); } public NewInvoiceNameCommandBuilder withInvoiceDate(Date invoiceDate) { this.invoiceDate = invoiceDate; return this; } public NewInvoiceNameCommandBuilder withInvoiceId(String invoiceId) { this.invoiceId = invoiceId; return this; } [...] } } private final Date invoiceDate; private final String invoiceId; private final String userId; private final String firmId; private final boolean directInvoice; private final boolean firmInvoice; private final boolean electronic; private NewInvoiceNameCommand( Date invoiceDate, String invoiceId, String userId, String firmId, boolean directInvoice, boolean firmInvoice, boolean electronic) { this.invoiceDate = invoiceDate; this.invoiceId = invoiceId; this.userId = userId; this.firmId = firmId; this.directInvoice = directInvoice; this.firmInvoice = firmInvoice; this.electronic = electronic; } public Date getInvoiceDate() { return invoiceDate; } public String getInvoiceId() { return invoiceId; } public String getUserId() { return userId; } public String getFirmId() { return firmId; } public boolean isDirectInvoice() { return directInvoice; } public boolean isFirmInvoice() { return firmInvoice; } public boolean isElectronic() { return electronic; }
21. NewInvoiceNameCommand newInvoiceNameCommand = new NewInvoiceNameCommand.NewInvoiceNameCommandBuilder() .withInvoiceDate(new Date()) .withInvoiceId("45AE-45F") .withUserId("872346") .withFirmId("abc-234") .withDirectInvoice(true) .withFirmInvoice(false) .withElectronic(false) .build(); String newInvoiceId = invoiceCreator.createInvoiceName(newInvoiceNameCommand);
22. with default values
23. public class NewInvoiceNameCommand { public static class NewInvoiceNameCommandBuilder { private Date invoiceDate; private String invoiceId; private String userId; private String firmId; private boolean directInvoice; private boolean firmInvoice; private boolean electronic; public NewInvoiceNameCommandBuilder() { // default values this.directInvoice = true; this.firmInvoice = false; } public NewInvoiceNameCommand build() { return new NewInvoiceNameCommand( invoiceDate, invoiceId, userId, firmId, directInvoice, firmInvoice, electronic); }
24. NewInvoiceNameCommand newInvoiceNameCommand = new NewInvoiceNameCommand.NewInvoiceNameCommandBuilder() .withInvoiceDate(new Date()) .withInvoiceId("45AE-45F") .withUserId("872346") .withFirmId("abc-234") .withElectronic(false) .build(); String newInvoiceId = invoiceCreator.createInvoiceName(newInvoiceNameCommand);
25. better!
26. just need some glue
27. public class NewInvoiceNameCommand { public static class NewInvoiceNameCommandBuilder { private Date invoiceDate; private String invoiceId; private String userId; private String firmId; private boolean directInvoice; private boolean firmInvoice; private boolean electronic; public NewInvoiceNameCommandBuilder() { // default values this.directInvoice = true; this.firmInvoice = false; } public NewInvoiceNameCommand build() { return new NewInvoiceNameCommand( invoiceDate, invoiceId, userId, firmId, directInvoice, firmInvoice, electronic); } public NewInvoiceNameCommandBuilder withInvoiceDate(Date invoiceDate) { this.invoiceDate = invoiceDate; return this; } public NewInvoiceNameCommandBuilder withInvoiceId(String invoiceId) { this.invoiceId = invoiceId; return this; } public NewInvoiceNameCommandBuilder withUserId(String userId) { this.userId = userId; return this; } public NewInvoiceNameCommandBuilder withFirmId(String firmId) { this.firmId = firmId; return this; } public NewInvoiceNameCommandBuilder withDirectInvoice(boolean directInvoice) { this.directInvoice = directInvoice; return this; } public NewInvoiceNameCommandBuilder withFirmInvoice(boolean firmInvoice) { this.firmInvoice = firmInvoice; return this; } public NewInvoiceNameCommandBuilder withElectronic(boolean electronic) { this.electronic = electronic; return this; } } private final Date invoiceDate; private final String invoiceId; private final String userId; private final String firmId; private final boolean directInvoice; private final boolean firmInvoice; private final boolean electronic; private NewInvoiceNameCommand( Date invoiceDate, String invoiceId, String userId, String firmId, boolean directInvoice, boolean firmInvoice, boolean electronic) { this.invoiceDate = invoiceDate; this.invoiceId = invoiceId; this.userId = userId; this.firmId = firmId; this.directInvoice = directInvoice; this.firmInvoice = firmInvoice; this.electronic = electronic; } public Date getInvoiceDate() { return invoiceDate; } public String getInvoiceId() { return invoiceId; } public String getUserId() { return userId; } public String getFirmId() { return firmId; } public boolean isDirectInvoice() { return directInvoice; } public boolean isFirmInvoice() { return firmInvoice; } public boolean isElectronic() { return electronic; } }
28. let's try with Scala
29. def createInvoiceName( invoiceDate: Date, invoiceId: String, userId: String, firmId: String, directInvoice: Boolean, firmInvoice: Boolean, electronic: Boolean): String = { // ... }
30. val newInvoiceId = invoiceCreator.createInvoiceName( new Date, "45AE-45F", "872346", "abc-234", true, false, false )
31. Scala can be ugly too (surprise #1)
32. val newInvoiceId = invoiceCreator.createInvoiceName( new Date, // invoiceDate "45AE-45F", // invoiceId "872346", // userId "abc-234", // firmId true, // directInvoice false, // firmInvoice false // electronic )
33. comments exist in Scala (surprise #2)
34. val newInvoiceId = invoiceCreator.createInvoiceName( invoiceDate = new Date, invoiceId = "45AE-45F", userId = "872346", firmId = "abc-234", directInvoice = true, firmInvoice = false, electronic = false )
35. Yes, named parameters!
36. and default values?
37. def createInvoiceName( invoiceDate: Date, invoiceId: String, userId: String, firmId: String, directInvoice: Boolean = true, firmInvoice: Boolean = false, electronic: Boolean): String = {
38. val newInvoiceId = invoiceCreator.createInvoiceName( invoiceDate = new Date, invoiceId = "45AE-45F", userId = "872346", firmId = "abc-234", electronic = false )
39. but I want a command object
40. case class NewInvoiceNameCommand ( invoiceDate: Date, invoiceId: String, userId: String, firmId: String, directInvoice: Boolean = true, firmInvoice: Boolean = false, electronic: Boolean )
41. val newInvoiceNameCommand = NewInvoiceNameCommand ( invoiceDate = new Date, invoiceId = "45AE-45F", userId = "872346", firmId = "abc-234", electronic = false ) val newInvoiceId = invoiceCreator.createInvoiceName( newInvoiceNameCommand)
42. Java can be pain #2
43. public int multiplyBy2(int number) { return number * 2; } [...] public void multiplyUserInputBy2() { Integer userInput = null; multiplyBy2(userInput); }
44. def multiplyBy2(number: Int): Int = { number * 2 } def multiplyUserInputBy2 { //val userInput: Int = null // does not compile //val userInput = Int.unbox(new Integer(null)) throws exception val userInput = 2 multiplyBy2(userInput) }
45. Java can be pain #3
46. public class User { private final String name; private final String gender; private final Date dateOfBirth; public User(String name, String gender, Date dateOfBirth) { this.name = name; this.gender = gender; this.dateOfBirth = dateOfBirth; } public String getName() { return name; } public String getGender() { return gender; } public Date getDateOfBirth() { return dateOfBirth; } }
47. public class User { private final String name; private final String gender; private final Date dateOfBirth; public User(String name, String gender, Date dateOfBirth) { this.name = name; this.gender = gender; this.dateOfBirth = dateOfBirth; } public String getName() { return name; } public String getGender() { return gender; } public Date getDateOfBirth() { return dateOfBirth; } public Integer getAge() { if (dateOfBirth == null) { return null; } Date now = new Date(); long difference = now.getTime() - dateOfBirth.getTime(); Calendar yearCalculator = Calendar.getInstance(); yearCalculator.setTimeInMillis(difference); return yearCalculator.get(Calendar.YEAR); } }
48. public class UserBusiness { private final UserRepository userRepository = new UserRepository(); public boolean isUserAllowed(String name) { User user = userRepository.findUserByName(name); if (user != null) { if (user.getGender() != null && user.getGender().equals("F")) { if (user.getAge() != null && user.getAge() >= 18) { return true; } } } return false; } }
49. case class User ( name: String, gender: Option[String] = None, dateOfBirth: Option[Date] = None ) { def age: Option[Int] = dateOfBirth.map { dob => calculateAge(dob) } private def calculateAge(dateOfBirth: Date): Int = { val now = new Date() val difference = now.getTime - dateOfBirth.getTime val yearCalculator = Calendar.getInstance() yearCalculator.setTimeInMillis(difference) yearCalculator.get(Calendar.YEAR) } }
50. class UserBusiness { val userRepository = new UserRepository() def isUserAllowed(name: String): Boolean = { val allowedUser = for { user <- userRepository.findUserByName(name) gender <- user.gender if gender == "F" age <- user.age if age >= 18 } yield user allowedUser.isDefined } }
51. Bye bye NullPointerException
52. Asynchronous IO
53. Asynchronous IO - What?
57. Asynchronous IO - Why?
62. Asynchronous IO in Java
63. public Promise<JsonNode> searchStock(String query) { Promise<WS.Response> responsePromise = WS.url("http://localhost:9001/search") .setQueryParameter("query", query) .get(); return responsePromise.map(new F.Function<WS.Response, JsonNode>() { @Override public JsonNode apply(WS.Response response) throws Throwable { if (response.getStatus() == 200) { JsonNode jsonNode = response.asJson(); return jsonNode.findPath("results"); } else { throw new Exception("Error calling search service.\nResponse status " + response.getStatus() + "\n"); } } }); }
64. Asynchronous IO in Scala
65. def searchStock(query: String): Future[Seq[JsObject]] = { WS.url("http://localhost:9001/search") .withQueryString("query" -> query) .get() .map { response => response.status match { case 200 => (response.json \ "results").as[Seq[JsObject]] case _ => throw new Exception(s"Error calling search service.\nResponse status ${response.status}\n") } } }
66. Three sequential calls
67. public static Promise<Result> index(String userId) { Promise<User> user = backends.getUserById(userId); Promise<List<Order>> orders = user.flatMap(new F.Function<User, Promise<List<Order>>>() { @Override public Promise<List<Order>> apply(User user) throws Throwable { return backends.getOrdersForUser(user.getEmail()); } }); Promise<List<Product>> products = orders.flatMap(new F.Function<List<Order>, Promise<List<Product>>>() { @Override public Promise<List<Product>> apply(List<Order> orders) throws Throwable { return backends.getProductsForOrders(orders); } }); Promise<List<Stock>> stocks = products.flatMap(new F.Function<List<Product>, Promise<List<Stock>>>() { @Override public Promise<List<Stock>> apply(List<Product> products) throws Throwable { return backends.getStocksForProducts(products); } }); Promise<List<Object>> promises = Promise.sequence(user, orders, products, stocks); return promises.map(new F.Function<List<Object>, Result>() { @Override public Result apply(List<Object> results) throws Throwable { User user = (User)results.get(0); List<Order> orders = (List<Order>)results.get(1); List<Product> products = (List<Product>)results.get(2); List<Stock> stocks = (List<Stock>)results.get(3); return ok(orders.size() + " order(s) for user " + user.getEmail()); } }); }
68. def index(userId: String) = Action.async { for { user <- getUserById(userId) orders <- getOrdersForUser(user.email) products <- getProductsForOrders(orders) stocks <- getStocksForProducts(products) } yield Ok(s"${orders.size} order(s) for user ${user.email}") }
69. OK, I want to try Scala
70. Be careful
71. Scala can be pain #1
72. ✗ slow compilation
73. ✗ slow compilation incremental compilation ~run modules Scala 2.11
74. Scala can be pain #2
75. functional programming terrorists
76. use the most appropriate style for the problem (and for the maintenance)
77. Scala can be pain #3
78. # Scala dev < Java
79. use this problem as opportunity Ex: “Yes, all of us were quite experienced Java programmers. [...] Because we were all learning together, this worked really well.”
80. Online courses: Functional Programming Principles in Scala Principles of Reactive Programming
81. Scala User Group Play framework User Group
82. Trainings http://www.leanovate.de/training/software/
83. I get it I want to try Scala
84. Integration in my project?
85. ✔ Maven ✔ ANT ✔ SBT ✔ Gradle
86. Begin with scala-test?
87. test("content disposition parser extracts the filename") { val header = "Attachment; filename=example.html" val filename = ContentDispositionHeader.parse(header).filename assert(filename === Some("example.html")) }
88. it should "replace ä with ae" in { SwiftLatinCharset.from("fooÄfoo") shouldEqual "fooAefoo" SwiftLatinCharset.from("fooäfoo") shouldEqual "fooaefoo" }
89. Integration in my firm?
90. Continuous Integration
91. sbt test mvn test ...
92. ✔ ✔ ✔
93. Scala ✔ Integrate with Java ✔ Integrate with existing build ✔ Usual tools
94. Build products ✔ efficient development ✔ motivated teams ✔ enable SOA (async IO) ✔ less lines of code ✔ easier maintenance
95. ✔ focus on your product!
96. thanks for your attention