Add Kotlin data mapping examples (BAEL-2247) (eugenp#5560)

Author: kiview

core-kotlin/README.md

@@ -40,3 +40,4 @@
 - [Converting Kotlin Data Class from JSON using GSON](https://www.baeldung.com/kotlin-json-convert-data-class)
 - [Concatenate Strings in Kotlin](https://www.baeldung.com/kotlin-concatenate-strings)
 - [Kotlin return, break, continue Keywords](https://www.baeldung.com/kotlin-return-break-continue)
+- [Mapping of Data Objects in Kotlin](https://www.baeldung.com/kotlin-data-objects-mapping)

core-kotlin/src/main/kotlin/com/baeldung/datamapping/User.kt

@@ -0,0 +1,10 @@
+package com.baeldung.datamapping
+
+data class User(
+        val firstName: String,
+        val lastName: String,
+        val street: String,
+        val houseNumber: String,
+        val phone: String,
+        val age: Int,
+        val password: String)

core-kotlin/src/main/kotlin/com/baeldung/datamapping/UserExtensions.kt

@@ -0,0 +1,22 @@
+package com.baeldung.datamapping
+
+import kotlin.reflect.full.memberProperties
+
+fun User.toUserView() = UserView(
+        name = "$firstName $lastName",
+        address = "$street $houseNumber",
+        telephone = phone,
+        age = age
+)
+
+fun User.toUserViewReflection() = with(::UserView) {
+    val propertiesByName = User::class.memberProperties.associateBy { it.name }
+    callBy(parameters.associate { parameter ->
+        parameter to when (parameter.name) {
+            UserView::name.name -> "$firstName $lastName"
+            UserView::address.name -> "$street $houseNumber"
+            UserView::telephone.name -> phone
+            else -> propertiesByName[parameter.name]?.get(this@toUserViewReflection)
+        }
+    })
+}

core-kotlin/src/main/kotlin/com/baeldung/datamapping/UserView.kt

@@ -0,0 +1,8 @@
+package com.baeldung.datamapping
+
+data class UserView(
+        val name: String,
+        val address: String,
+        val telephone: String,
+        val age: Int
+)

core-kotlin/src/test/kotlin/com/baeldung/datamapping/UserTest.kt

@@ -0,0 +1,43 @@
+package com.baeldung.datamapping
+
+import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.assertAll
+import kotlin.test.assertEquals
+
+class UserTest {
+
+    @Test
+    fun `maps User to UserResponse using extension function`() {
+        val p = buildUser()
+        val view = p.toUserView()
+        assertUserView(view)
+    }
+
+    @Test
+    fun `maps User to UserResponse using reflection`() {
+        val p = buildUser()
+        val view = p.toUserViewReflection()
+        assertUserView(view)
+    }
+
+    private fun buildUser(): User {
+        return User(
+                "Java",
+                "Duke",
+                "Javastreet",
+                "42",
+                "1234567",
+                30,
+                "s3cr37"
+        )
+    }
+
+    private fun assertUserView(pr: UserView) {
+        assertAll(
+                { assertEquals("Java Duke", pr.name) },
+                { assertEquals("Javastreet 42", pr.address) },
+                { assertEquals("1234567", pr.telephone) },
+                { assertEquals(30, pr.age) }
+        )
+    }
+}