Add k6 tests

virtual-threads-app/src/main/java/com/zeenea/experiments/virtualthreads/virtualthreadsapp/domain/marketplace/MarketplaceService.java

@@ -8,7 +8,7 @@ import com.zeenea.experiments.virtualthreads.virtualthreadsapp.domain.marketplac
 import org.springframework.stereotype.Service;
 
 import java.util.List;
-import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.*;
 
 @Service
 public class MarketplaceService {
@@ -21,9 +21,12 @@ public class MarketplaceService {
     }
 
     public Marketplace getMarketplace() {
-        return getMarketplaceInParallel();
+        return getMarketplaceInParallel2();
     }
 
+    /**
+     * This method uses classic threads while it is using `CompletableFuture`s. This way should be avoided.
+     */
     private Marketplace getMarketplaceInParallel() {
         CompletableFuture<List<Catalog>> getCatalogsFuture = CompletableFuture.supplyAsync(catalogService::getAll);
         CompletableFuture<List<Item>> getAllItemsFuture = CompletableFuture.supplyAsync(itemService::getAllItems);
@@ -38,6 +41,23 @@ public class MarketplaceService {
         return new Marketplace(catalogs, sharedItems);
     }
 
+    private Marketplace getMarketplaceInParallel2() {
+        try (ExecutorService executorService = Executors.newVirtualThreadPerTaskExecutor()) {
+            Future<List<Catalog>> getCatalogsFuture = executorService.submit(catalogService::getAll);
+            Future<List<Item>> getItemsFuture = executorService.submit(itemService::getAllItems);
+
+            List<Catalog> catalogs = getCatalogsFuture.get();
+            List<Item> items = getItemsFuture.get();
+
+            var sharedItems = items.stream()
+                    .filter(Item::isShared)
+                    .toList();
+            return new Marketplace(catalogs, sharedItems);
+        } catch (ExecutionException | InterruptedException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
     private Marketplace getMarketplaceSequentially() {
         return new Marketplace(
                 catalogService.getAll(),