Add Spring boot with Rest controller

src/main/kotlin/Main.kt

@@ -1,5 +0,0 @@
-package org.example
-
-fun main() {
-    println("Hello World!")
-}

src/main/kotlin/org/example/Application.kt

@@ -0,0 +1,11 @@
+package org.example
+
+import org.springframework.boot.autoconfigure.SpringBootApplication
+import org.springframework.boot.runApplication
+
+@SpringBootApplication
+class Application
+
+fun main(args: Array<String>) {
+    runApplication<Application>(*args)
+}

src/main/kotlin/org/example/HelloController.kt

@@ -0,0 +1,13 @@
+package org.example
+
+import org.springframework.web.bind.annotation.GetMapping
+import org.springframework.web.bind.annotation.RestController
+
+@RestController
+class HelloController {
+
+    @GetMapping("/hello")
+    fun sayHello(): String {
+        return "Hello, World!"
+    }
+}