首先要說明,Kotlin支持你所知道的全部Java框架和庫,包括但不限於Spring全家桶、Guice、Hibernate、MyBatis、Jackson等,甚至有人在用Kotlin寫Spark大數據程序,所以Kotlin不須要專門的框架。所以,爲Kotlin開發框架的人,都是懷着滿滿的愛!java
Kotlin如今主要流行於Android開發,我是搞後端開發的,不熟悉Android,就不妄言了。這篇文章主要介紹後端框架,包括Web、SQL、依賴注入、測試這些方面。git
- An HTTP Framework https://github.com/wasabifx/wasabigithub
極簡的Web框架,基於Netty構建,編程風格效仿了Ruby的Sinatra和Node.js的Express。web
Java也有個效仿Sinatra風格的Web框架,叫Spark(是的,與某大數據框架重名了)。sql
使用很簡單:編程
var server = AppServer() server.get("/", { response.send("Hello World!") }) server.start()
也能夠這麼寫:json
server.get(「/「) { response.send("Hello World!") }
加一個前置攔截器(next()
表示進入下一步處理):後端
server.get("/", { val log = Log() log.info("URI requested is ${request.uri}") next() }, { response.send("Hello World!", "application/json") } )
獲取參數:安全
server.get("/customer/:id", { val customerId = request.routeParams["id"] } )
server.get("/customer", { val customerName = request.queryParams["name"] } )
爲了提供可維護性,能夠在別處定義一個方法,在程序入口引用它:app
appServer.get("/customer", ::getCustomer)
這種微框架很適合快速爲一個後端服務添加REST接口。
https://github.com/TinyMissio...
JetBrains官方支持的Web框架,特點是類型安全的HTML DSL和CSS DSL (風格相似Haml/Slim和SASS/LESS)
由於Kotlin是支持動態執行代碼的,因此DSL理論上是能夠熱修改的,可是不知道Kara框架有沒有內置這個特性。
HTML View:
class Index() : HtmlView() { override fun render(context: ActionContext) { h2("Welcome to Kara") p("Your app is up and running, now it's time to make something!") p("Start by editing this file here: src/com/karaexample/views/home/Index.kt") } }
HTML Layout:
class DefaultLayout() : HtmlLayout() { override fun render(context: ActionContext, mainView: HtmlView) { head { title("Kara Demo Title") stylesheet(DefaultStyles()) } body { h1("Kara Demo Site") div(id="main") { renderView(context, mainView) } a(text="Kara is developed by Tiny Mission", href="http://tinymission.com") } } }
Forms:
class BookForm(val book : Book) : HtmlView() { override fun render(context: ActionContext) { h2("Book Form") formFor(book, "/updatebook", FormMethod.Post) { p { labelFor("title") textFieldFor("title") } p { labelFor("isPublished", "Is Published?") checkBoxFor("isPublished") } } } }
CSS:
class DefaultStyles() : Stylesheet() { override fun render() { s("body") { backgroundColor = c("#f0f0f0") } s("#main") { width = 85.percent backgroundColor = c("#fff") margin = box(0.px, auto) padding = box(1.em) border = "1px solid #ccc" borderRadius = 5.px } s("input[type=text], textarea") { padding = box(4.px) width = 300.px } s("textarea") { height = 80.px } s("table.fields") { s("td") { padding = box(6.px, 3.px) } s("td.label") { textAlign = TextAlign.right } s("td.label.top") { verticalAlign = VerticalAlign.top } } } }
其實就是在寫Kotlin代碼,顯然你能夠自行擴展出更多的DSL,還能夠用面向對象或函數式的方式來複用。
不須要用到反射,性能更高:
object Home { val layout = DefaultLayout() Get("/") class Index() : Request({ karademo.views.home.Index() }) Get("/test") class Test() : Request({ TextResult("This is a test action, yo") }) Post("/updatebook") class Update() : Request({ redirect("/forms") }) Get("/complex/*/list/:id") Complex(id : Int) : Request({ TextResult("complex: ${params[0]} id = ${params["id"]}") }) }
實現這個接口並綁定到路由路徑就能夠了:
/** * Base class for Kara middleware. * Middleware is code that is injected inside the request pipeline, * either before or after a request is handled by the application. */ abstract class Middleware() { /** * Gets called before the application is allowed to handle the request. * Return false to stop the request pipeline from executing anything else. */ abstract fun beforeRequest(context : ActionContext) : Boolean /** * Gets called after the application is allowed to handle the request. * Return false to stop the request pipeline from executing anything else. */ abstract fun afterRequest(context : ActionContext) : Boolean }
appConfig.middleware.add(MyMiddleware(), "/books")
綜合來講,Kara確實是比較優秀的web框架。
但有一點很差,默認使用3000端口,與Rails重複了。
https://github.com/jetbrains/...
JetBrains官方支持的SQL/ORM框架,風格頗爲相似Django ORM,而且充分發揮了Kotlin的強類型優點。
項目主頁有很長一段示例代碼,全程都是強類型,很是流暢,使人賞心悅目:
import org.jetbrains.exposed.sql.* import org.jetbrains.exposed.sql.transactions.transaction import org.jetbrains.exposed.sql.SchemaUtils.create import org.jetbrains.exposed.sql.SchemaUtils.drop object Users : Table() { val id = varchar("id", 10).primaryKey() // Column<String> val name = varchar("name", length = 50) // Column<String> val cityId = (integer("city_id") references Cities.id).nullable() // Column<Int?> } object Cities : Table() { val id = integer("id").autoIncrement().primaryKey() // Column<Int> val name = varchar("name", 50) // Column<String> } fun main(args: Array<String>) { Database.connect("jdbc:h2:mem:test", driver = "org.h2.Driver") transaction { create (Cities, Users) val saintPetersburgId = Cities.insert { it[name] = "St. Petersburg" } get Cities.id val munichId = Cities.insert { it[name] = "Munich" } get Cities.id Cities.insert { it[name] = "Prague" } Users.insert { it[id] = "andrey" it[name] = "Andrey" it[cityId] = saintPetersburgId } Users.insert { it[id] = "sergey" it[name] = "Sergey" it[cityId] = munichId } Users.insert { it[id] = "eugene" it[name] = "Eugene" it[cityId] = munichId } Users.insert { it[id] = "alex" it[name] = "Alex" it[cityId] = null } Users.insert { it[id] = "smth" it[name] = "Something" it[cityId] = null } Users.update({Users.id eq "alex"}) { it[name] = "Alexey" } Users.deleteWhere{Users.name like "%thing"} println("All cities:") for (city in Cities.selectAll()) { println("${city[Cities.id]}: ${city[Cities.name]}") } println("Manual join:") (Users innerJoin Cities).slice(Users.name, Cities.name). select {(Users.id.eq("andrey") or Users.name.eq("Sergey")) and Users.id.eq("sergey") and Users.cityId.eq(Cities.id)}.forEach { println("${it[Users.name]} lives in ${it[Cities.name]}") } println("Join with foreign key:") (Users innerJoin Cities).slice(Users.name, Users.cityId, Cities.name). select {Cities.name.eq("St. Petersburg") or Users.cityId.isNull()}.forEach { if (it[Users.cityId] != null) { println("${it[Users.name]} lives in ${it[Cities.name]}") } else { println("${it[Users.name]} lives nowhere") } } println("Functions and group by:") ((Cities innerJoin Users).slice(Cities.name, Users.id.count()).selectAll().groupBy(Cities.name)).forEach { val cityName = it[Cities.name] val userCount = it[Users.id.count()] if (userCount > 0) { println("$userCount user(s) live(s) in $cityName") } else { println("Nobody lives in $cityName") } } drop (Users, Cities) } }
CRUD和各類查詢都很容易表達,也能自動建表,確實方便得很。
可是文檔沒提到schema migration,想必是沒這個功能。若是你想修改表結構,還得手動用SQL去改?這方面須要提升。
https://github.com/requery/re...
這是一個主要面向Android的Java ORM框架,爲Kotlin提供了一些額外特性。
你須要把實體聲明爲abstract class或interface,而後標上相似JPA的註解:
@Entity abstract class AbstractPerson { @Key @Generated int id; @Index("name_index") // table specification String name; @OneToMany // relationships 1:1, 1:many, many to many Set<Phone> phoneNumbers; @Converter(EmailToStringConverter.class) // custom type conversion Email email; @PostLoad // lifecycle callbacks void afterLoad() { updatePeopleList(); } // getter, setters, equals & hashCode automatically generated into Person.java }
@Entity public interface Person { @Key @Generated int getId(); String getName(); @OneToMany Set<Phone> getPhoneNumbers(); String getEmail(); }
它提供了SQL DSL,看起來彷佛依賴代碼生成:
Result<Person> query = data .select(Person.class) .where(Person.NAME.lower().like("b%")).and(Person.AGE.gt(20)) .orderBy(Person.AGE.desc()) .limit(5) .get();
用Kotlin能夠寫得更簡潔:
data { val result = select(Person::class) where (Person::age gt 21) and (Person::name eq "Bob") limit 10 }
https://github.com/andrewoma/...
https://github.com/x2bool/kuery
https://github.com/seratch/ko...
這三個其實是SQL庫,對JDBC作了一些封裝,提供了簡易的SQL DSL。我不想用篇幅來介紹,有興趣的朋友能夠去項目主頁看一看。
還要特別推薦Ebean ORM框架 https://ebean-orm.github.io/ 融合了JPA和Active Record的風格,成熟度相對高一些,已有必定規模的用戶羣,雖然不是專爲Kotlin設計,但做者也在使用Kotlin。
https://github.com/SalomonBry...
用法簡單,支持scopes, modules, lazy等特性。
val kodein = Kodein { bind<Dice>() with provider { RandomDice(0, 5) } bind<DataSource>() with singleton { SqliteDS.open("path/to/file") } } class Controller(private val kodein: Kodein) { private val ds: DataSource = kodein.instance() }
我的認爲Kodein沒有什麼亮點。
由於傳統的Spring和Guice都是能夠用的,功能和穩定性更有保證,因此建議繼續用傳統的吧。
https://github.com/JetBrains/...
JetBrains官方支持的規格測試框架,效仿了Ruby的RSpec,代碼風格很類似,可讀性很好:
class SimpleTest : Spek({ describe("a calculator") { val calculator = SampleCalculator() it("should return the result of adding the first number to the second number") { val sum = calculator.sum(2, 4) assertEquals(6, sum) } it("should return the result of subtracting the second number from the first number") { val subtract = calculator.subtract(4, 2) assertEquals(2, subtract) } } })
除此以外,Java的JUnit, TestNG, Mockito等框架在Kotlin中都是可使用的。
相比於Scala,Kotlin在實用性方面下了大功夫,無縫兼容Java,融入Java生態,自身也有簡潔的語法和強大的DSL能力。(想想Scala 2.10 2.11 2.12的互不兼容,以及build一個項目會下載標準庫的n個版本,例如2.11.0、2.11.一、2.11.2,也不知道實際運行的是哪一個。)
這些新興的Kotlin框架延續了Kotlin的簡潔和強大,相信它們很快就會展示出光明的前途!