BAEL-1462 Kotlin DI with Kodein (#3544)

* BAEL-1462 Kotlin DI with Kodein

* BAEL-1462 Kotlin DI with Kodein

* applied editor's suggestions
* removed unnecessary curly braces

* Moved kodein files into core-kotlin as per editor's review

* Using assertj instead of junit assertions as per editor's instruction

core-kotlin/pom.xml

@@ -76,7 +76,18 @@
             <artifactId>mockito-kotlin</artifactId>
             <version>${mockito-kotlin.version}</version>
             <scope>test</scope>
-        </dependency>        
+        </dependency>
+        <dependency>
+            <groupId>com.github.salomonbrys.kodein</groupId>
+            <artifactId>kodein</artifactId>
+            <version>${kodein.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
     <build>
@@ -189,11 +200,13 @@
         <kotlin-reflect.version>1.1.2</kotlin-reflect.version>
         <kotlinx.version>0.15</kotlinx.version>
         <mockito-kotlin.version>1.5.0</mockito-kotlin.version>
+        <kodein.version>4.1.0</kodein.version>
 
         <junit.jupiter.version>5.0.0</junit.jupiter.version>
         <junit.platform.version>1.0.0</junit.platform.version>
         <junit.vintage.version>4.12.0</junit.vintage.version>
         <junit4.version>4.12</junit4.version>
+        <assertj.version>3.9.1</assertj.version>
     </properties>
 
 </project>

core-kotlin/src/main/kotlin/com/baeldung/kotlin/kodein/Controller.kt

@@ -0,0 +1,3 @@
+package com.baeldung.kotlin.kodein
+
+class Controller(private val service : Service)

core-kotlin/src/main/kotlin/com/baeldung/kotlin/kodein/Dao.kt

@@ -0,0 +1,3 @@
+package com.baeldung.kotlin.kodein
+
+interface Dao

core-kotlin/src/main/kotlin/com/baeldung/kotlin/kodein/JdbcDao.kt

@@ -0,0 +1,3 @@
+package com.baeldung.kotlin.kodein
+
+class JdbcDao : Dao

core-kotlin/src/main/kotlin/com/baeldung/kotlin/kodein/MongoDao.kt

@@ -0,0 +1,3 @@
+package com.baeldung.kotlin.kodein
+
+class MongoDao : Dao

core-kotlin/src/main/kotlin/com/baeldung/kotlin/kodein/Service.kt

@@ -0,0 +1,3 @@
+package com.baeldung.kotlin.kodein
+
+class Service(private val dao: Dao, private val tag: String)

core-kotlin/src/test/kotlin/com/baeldung/kotlin/kodein/KodeinUnitTest.kt

@@ -0,0 +1,191 @@
+package com.baeldung.kotlin.kodein
+
+import com.github.salomonbrys.kodein.*
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.Test
+
+class KodeinUnitTest {
+
+    class InMemoryDao : Dao
+
+    @Test
+    fun whenSingletonBinding_thenSingleInstanceIsCreated() {
+        var created = false
+        val kodein = Kodein {
+            bind<Dao>() with singleton {
+                created = true
+                MongoDao()
+            }
+        }
+
+        assertThat(created).isFalse()
+
+        val dao1: Dao = kodein.instance()
+
+        assertThat(created).isTrue()
+
+        val dao2: Dao = kodein.instance()
+
+        assertThat(dao1).isSameAs(dao2)
+    }
+
+    @Test
+    fun whenFactoryBinding_thenNewInstanceIsCreated() {
+        val kodein = Kodein {
+            bind<Dao>() with singleton { MongoDao() }
+            bind<Service>() with factory { tag: String -> Service(instance(), tag) }
+        }
+        val service1: Service = kodein.with("myTag").instance()
+        val service2: Service = kodein.with("myTag").instance()
+
+        assertThat(service1).isNotSameAs(service2)
+    }
+
+    @Test
+    fun whenProviderBinding_thenNewInstanceIsCreated() {
+        val kodein = Kodein {
+            bind<Dao>() with provider { MongoDao() }
+        }
+        val dao1: Dao = kodein.instance()
+        val dao2: Dao = kodein.instance()
+
+        assertThat(dao1).isNotSameAs(dao2)
+    }
+
+    @Test
+    fun whenTaggedBinding_thenMultipleInstancesOfSameTypeCanBeRegistered() {
+        val kodein = Kodein {
+            bind<Dao>("dao1") with singleton { MongoDao() }
+            bind<Dao>("dao2") with singleton { MongoDao() }
+        }
+        val dao1: Dao = kodein.instance("dao1")
+        val dao2: Dao = kodein.instance("dao2")
+
+        assertThat(dao1).isNotSameAs(dao2)
+    }
+
+    @Test
+    fun whenEagerSingletonBinding_thenCreationIsEager() {
+        var created = false
+        val kodein = Kodein {
+            bind<Dao>() with eagerSingleton {
+                created = true
+                MongoDao()
+            }
+        }
+
+        assertThat(created).isTrue()
+        val dao1: Dao = kodein.instance()
+        val dao2: Dao = kodein.instance()
+
+        assertThat(dao1).isSameAs(dao2)
+    }
+
+    @Test
+    fun whenMultitonBinding_thenInstancesAreReused() {
+        val kodein = Kodein {
+            bind<Dao>() with singleton { MongoDao() }
+            bind<Service>() with multiton { tag: String -> Service(instance(), tag) }
+        }
+        val service1: Service = kodein.with("myTag").instance()
+        val service2: Service = kodein.with("myTag").instance()
+
+        assertThat(service1).isSameAs(service2)
+    }
+
+    @Test
+    fun whenInstanceBinding_thenItIsReused() {
+        val dao = MongoDao()
+        val kodein = Kodein {
+            bind<Dao>() with instance(dao)
+        }
+        val fromContainer: Dao = kodein.instance()
+
+        assertThat(dao).isSameAs(fromContainer)
+    }
+
+    @Test
+    fun whenConstantBinding_thenItIsAvailable() {
+        val kodein = Kodein {
+            constant("magic") with 42
+        }
+        val fromContainer: Int = kodein.instance("magic")
+
+        assertThat(fromContainer).isEqualTo(42)
+    }
+
+    @Test
+    fun whenUsingModules_thenTransitiveDependenciesAreSuccessfullyResolved() {
+        val jdbcModule = Kodein.Module {
+            bind<Dao>() with singleton { JdbcDao() }
+        }
+        val kodein = Kodein {
+            import(jdbcModule)
+            bind<Controller>() with singleton { Controller(instance()) }
+            bind<Service>() with singleton { Service(instance(), "myService") }
+        }
+
+        val dao: Dao = kodein.instance()
+        assertThat(dao).isInstanceOf(JdbcDao::class.java)
+    }
+
+    @Test
+    fun whenComposition_thenBeansAreReUsed() {
+        val persistenceContainer = Kodein {
+            bind<Dao>() with singleton { MongoDao() }
+        }
+        val serviceContainer = Kodein {
+            extend(persistenceContainer)
+            bind<Service>() with singleton { Service(instance(), "myService") }
+        }
+        val fromPersistence: Dao = persistenceContainer.instance()
+        val fromService: Dao = serviceContainer.instance()
+
+        assertThat(fromPersistence).isSameAs(fromService)
+    }
+
+    @Test
+    fun whenOverriding_thenRightBeanIsUsed() {
+        val commonModule = Kodein.Module {
+            bind<Dao>() with singleton { MongoDao() }
+            bind<Service>() with singleton { Service(instance(), "myService") }
+        }
+        val testContainer = Kodein {
+            import(commonModule)
+            bind<Dao>(overrides = true) with singleton { InMemoryDao() }
+        }
+        val dao: Dao = testContainer.instance()
+
+        assertThat(dao).isInstanceOf(InMemoryDao::class.java)
+    }
+
+    @Test
+    fun whenMultiBinding_thenWorks() {
+        val kodein = Kodein {
+            bind() from setBinding<Dao>()
+            bind<Dao>().inSet() with singleton { MongoDao() }
+            bind<Dao>().inSet() with singleton { JdbcDao() }
+        }
+        val daos: Set<Dao> = kodein.instance()
+
+        assertThat(daos.map { it.javaClass as Class<*> }).containsOnly(MongoDao::class.java, JdbcDao::class.java)
+    }
+
+    @Test
+    fun whenInjector_thenWorks() {
+        class Controller2 {
+            private val injector = KodeinInjector()
+            val service: Service by injector.instance()
+            fun injectDependencies(kodein: Kodein) = injector.inject(kodein)
+        }
+
+        val kodein = Kodein {
+            bind<Dao>() with singleton { MongoDao() }
+            bind<Service>() with singleton { Service(instance(), "myService") }
+        }
+        val controller = Controller2()
+        controller.injectDependencies(kodein)
+
+        assertThat(controller.service).isNotNull
+    }
+}