add global exception handler for controllers

add new not found exception, add new test for ShopController

src/main/kotlin/com/example/demo/controllers/ShopController.kt

@@ -1,11 +1,11 @@
 package com.example.demo.controllers
 
+import com.example.demo.exceptions.NotFoundException
 import com.example.demo.provider.ShopProvider
 import jakarta.servlet.http.HttpServletResponse
 import kotlinx.serialization.json.Json
 import kotlinx.serialization.json.encodeToJsonElement
 import org.springframework.beans.factory.annotation.Autowired
-import org.springframework.http.HttpStatus
 import org.springframework.web.bind.annotation.GetMapping
 import org.springframework.web.bind.annotation.ResponseBody
 import org.springframework.web.bind.annotation.RestController
@@ -16,14 +16,9 @@ class ShopController (
 ) {
     @GetMapping(value = ["/shop/common-info"], produces = ["application/json"])
     @ResponseBody
+    @Throws(NotFoundException::class)
     fun commonInfo(response: HttpServletResponse): String {
-        val shop = shopProvider.getRandomShop()
-
-        if (shop == null) {
-            response.status = HttpStatus.NOT_FOUND.value()
-
-            return "not found"
-        }
+        val shop = shopProvider.getRandomShop() ?: throw NotFoundException()
 
         return Json.encodeToJsonElement(value = mapOf(
             "customers" to mapOf(

src/main/kotlin/com/example/demo/exceptions/ExceptionHandler.kt

@@ -0,0 +1,13 @@
+package com.example.demo.exceptions
+
+import com.example.demo.responses.makeNotFound
+import org.springframework.http.HttpStatus
+import org.springframework.http.ResponseEntity
+import org.springframework.web.bind.annotation.ControllerAdvice
+import org.springframework.web.bind.annotation.ExceptionHandler
+
+@ControllerAdvice
+class ExceptionHandler {
+    @ExceptionHandler(NotFoundException::class)
+    fun handleNotFound(): ResponseEntity<Any> = ResponseEntity(makeNotFound(), HttpStatus.NOT_FOUND)
+}

src/main/kotlin/com/example/demo/exceptions/NotFoundException.kt

@@ -0,0 +1,3 @@
+package com.example.demo.exceptions
+
+class NotFoundException: RuntimeException()

src/main/kotlin/com/example/demo/responses/BaseResponse.kt

@@ -0,0 +1,5 @@
+package com.example.demo.responses
+
+class BaseResponse(val status: ResponseStatus)
+
+fun makeNotFound(): BaseResponse = BaseResponse(status = ResponseStatus.NOT_FOUND)

src/main/kotlin/com/example/demo/responses/ResponseStatus.kt

@@ -0,0 +1,7 @@
+package com.example.demo.responses
+
+import com.fasterxml.jackson.annotation.JsonValue
+
+enum class ResponseStatus(@JsonValue val status: String) {
+    NOT_FOUND("not found");
+}