[BAEL-1401] Fuel HTTP Library with Kotlin (#5142)

* builder pattern in kotlin

* builder pattern in kotlin new-line

* deleted Sandbox, added unit test

* add other tests

* named and default parameters builder

* Make FoodOrderNamed a data class

* idiomatic Kotlin version

* Fuel HTTP library

* fuel pom property

* BAEL-1401 Removed extra pom.xml properties

core-kotlin/src/main/kotlin/com/baeldung/fuel/Interceptors.kt

@@ -0,0 +1,11 @@
+package com.baeldung.fuel
+
+import com.github.kittinunf.fuel.core.Request
+
+fun tokenInterceptor() = {
+    next: (Request) -> Request ->
+    { req: Request ->
+        req.header(mapOf("Authorization" to "Bearer AbCdEf123456"))
+        next(req)
+    }
+}

core-kotlin/src/main/kotlin/com/baeldung/fuel/Post.kt

@@ -0,0 +1,15 @@
+package com.baeldung.fuel
+
+import com.github.kittinunf.fuel.core.ResponseDeserializable
+import com.google.gson.Gson
+
+data class Post(var userId:Int,
+                var id:Int,
+                var title:String,
+                var body:String){
+
+
+    class Deserializer : ResponseDeserializable<Array<Post>> {
+        override fun deserialize(content: String): Array<Post> = Gson().fromJson(content, Array<Post>::class.java)
+    }
+}

core-kotlin/src/main/kotlin/com/baeldung/fuel/PostRoutingAPI.kt

@@ -0,0 +1,42 @@
+package com.baeldung.fuel
+
+import com.github.kittinunf.fuel.core.Method
+import com.github.kittinunf.fuel.util.FuelRouting
+
+sealed class PostRoutingAPI : FuelRouting {
+
+    override val basePath = "https://jsonplaceholder.typicode.com"
+
+    class posts(val id: String, override val body: String?): PostRoutingAPI()
+
+    class comments(val postId: String, override val body: String?): PostRoutingAPI()
+
+    override val method: Method
+        get() {
+            return when(this) {
+                is PostRoutingAPI.posts -> Method.GET
+                is PostRoutingAPI.comments -> Method.GET
+            }
+        }
+
+    override val path: String
+        get() {
+            return when(this) {
+                is PostRoutingAPI.posts -> "/posts"
+                is PostRoutingAPI.comments -> "/comments"
+            }
+        }
+
+    override val params: List<Pair<String, Any?>>?
+        get() {
+            return when(this) {
+                is PostRoutingAPI.posts -> listOf("id" to this.id)
+                is PostRoutingAPI.comments -> listOf("postId" to this.postId)
+            }
+        }
+
+    override val headers: Map<String, String>?
+        get() {
+            return null
+        }
+}