diff --git a/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/api/PetApi.java b/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/api/PetApi.java
index 0860e750a13..5cac886b443 100644
--- a/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/api/PetApi.java
+++ b/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/api/PetApi.java
@@ -17,7 +17,7 @@ import org.springframework.web.bind.annotation.RequestPart;
 import org.springframework.web.multipart.MultipartFile;
 
 import java.util.List;
-import java.util.concurrent.Callable;
+import java.util.concurrent.CompletableFuture;
 
 
 @Api(value = "pet", description = "the pet API")
@@ -35,9 +35,9 @@ public interface PetApi {
         produces = { "application/xml", "application/json" }, 
         consumes = { "application/json", "application/xml" },
         method = RequestMethod.POST)
-    default Callable<ResponseEntity<Void>> addPet(@ApiParam(value = "Pet object that needs to be added to the store" ,required=true ) @RequestBody Pet body) {
+    default CompletableFuture<ResponseEntity<Void>> addPet(@ApiParam(value = "Pet object that needs to be added to the store" ,required=true ) @RequestBody Pet body) {
         // do some magic!
-        return () -> new ResponseEntity<Void>(HttpStatus.OK);
+        return CompletableFuture.completedFuture(new ResponseEntity<Void>(HttpStatus.OK));
     }
 
 
@@ -52,10 +52,9 @@ public interface PetApi {
     @RequestMapping(value = "/pet/{petId}",
         produces = { "application/xml", "application/json" }, 
         method = RequestMethod.DELETE)
-    default Callable<ResponseEntity<Void>> deletePet(@ApiParam(value = "Pet id to delete",required=true ) @PathVariable("petId") Long petId,
-        @ApiParam(value = ""  ) @RequestHeader(value="api_key", required=false) String apiKey) {
+    default CompletableFuture<ResponseEntity<Void>> deletePet(@ApiParam(value = "Pet id to delete",required=true ) @PathVariable("petId") Long petId,@ApiParam(value = ""  ) @RequestHeader(value="api_key", required=false) String apiKey) {
         // do some magic!
-        return () -> new ResponseEntity<Void>(HttpStatus.OK);
+        return CompletableFuture.completedFuture(new ResponseEntity<Void>(HttpStatus.OK));
     }
 
 
@@ -71,9 +70,9 @@ public interface PetApi {
     @RequestMapping(value = "/pet/findByStatus",
         produces = { "application/xml", "application/json" }, 
         method = RequestMethod.GET)
-    default Callable<ResponseEntity<List<Pet>>> findPetsByStatus(@ApiParam(value = "Status values that need to be considered for filter", required = true) @RequestParam(value = "status", required = true) List<String> status) {
+    default CompletableFuture<ResponseEntity<List<Pet>>> findPetsByStatus(@ApiParam(value = "Status values that need to be considered for filter", required = true) @RequestParam(value = "status", required = true) List<String> status) {
         // do some magic!
-        return () -> new ResponseEntity<List<Pet>>(HttpStatus.OK);
+        return CompletableFuture.completedFuture(new ResponseEntity<List<Pet>>(HttpStatus.OK));
     }
 
 
@@ -89,9 +88,9 @@ public interface PetApi {
     @RequestMapping(value = "/pet/findByTags",
         produces = { "application/xml", "application/json" }, 
         method = RequestMethod.GET)
-    default Callable<ResponseEntity<List<Pet>>> findPetsByTags(@ApiParam(value = "Tags to filter by", required = true) @RequestParam(value = "tags", required = true) List<String> tags) {
+    default CompletableFuture<ResponseEntity<List<Pet>>> findPetsByTags(@ApiParam(value = "Tags to filter by", required = true) @RequestParam(value = "tags", required = true) List<String> tags) {
         // do some magic!
-        return () -> new ResponseEntity<List<Pet>>(HttpStatus.OK);
+        return CompletableFuture.completedFuture(new ResponseEntity<List<Pet>>(HttpStatus.OK));
     }
 
 
@@ -105,9 +104,9 @@ public interface PetApi {
     @RequestMapping(value = "/pet/{petId}",
         produces = { "application/xml", "application/json" }, 
         method = RequestMethod.GET)
-    default Callable<ResponseEntity<Pet>> getPetById(@ApiParam(value = "ID of pet to return",required=true ) @PathVariable("petId") Long petId) {
+    default CompletableFuture<ResponseEntity<Pet>> getPetById(@ApiParam(value = "ID of pet to return",required=true ) @PathVariable("petId") Long petId) {
         // do some magic!
-        return () -> new ResponseEntity<Pet>(HttpStatus.OK);
+        return CompletableFuture.completedFuture(new ResponseEntity<Pet>(HttpStatus.OK));
     }
 
 
@@ -125,9 +124,9 @@ public interface PetApi {
         produces = { "application/xml", "application/json" }, 
         consumes = { "application/json", "application/xml" },
         method = RequestMethod.PUT)
-    default Callable<ResponseEntity<Void>> updatePet(@ApiParam(value = "Pet object that needs to be added to the store" ,required=true ) @RequestBody Pet body) {
+    default CompletableFuture<ResponseEntity<Void>> updatePet(@ApiParam(value = "Pet object that needs to be added to the store" ,required=true ) @RequestBody Pet body) {
         // do some magic!
-        return () -> new ResponseEntity<Void>(HttpStatus.OK);
+        return CompletableFuture.completedFuture(new ResponseEntity<Void>(HttpStatus.OK));
     }
 
 
@@ -143,11 +142,9 @@ public interface PetApi {
         produces = { "application/xml", "application/json" }, 
         consumes = { "application/x-www-form-urlencoded" },
         method = RequestMethod.POST)
-    default Callable<ResponseEntity<Void>> updatePetWithForm(@ApiParam(value = "ID of pet that needs to be updated",required=true ) @PathVariable("petId") Long petId,
-        @ApiParam(value = "Updated name of the pet" ) @RequestPart(value="name", required=false)  String name,
-        @ApiParam(value = "Updated status of the pet" ) @RequestPart(value="status", required=false)  String status) {
+    default CompletableFuture<ResponseEntity<Void>> updatePetWithForm(@ApiParam(value = "ID of pet that needs to be updated",required=true ) @PathVariable("petId") Long petId,@ApiParam(value = "Updated name of the pet" ) @RequestPart(value="name", required=false)  String name,@ApiParam(value = "Updated status of the pet" ) @RequestPart(value="status", required=false)  String status) {
         // do some magic!
-        return () -> new ResponseEntity<Void>(HttpStatus.OK);
+        return CompletableFuture.completedFuture(new ResponseEntity<Void>(HttpStatus.OK));
     }
 
 
@@ -163,11 +160,9 @@ public interface PetApi {
         produces = { "application/json" }, 
         consumes = { "multipart/form-data" },
         method = RequestMethod.POST)
-    default Callable<ResponseEntity<ModelApiResponse>> uploadFile(@ApiParam(value = "ID of pet to update",required=true ) @PathVariable("petId") Long petId,
-        @ApiParam(value = "Additional data to pass to server" ) @RequestPart(value="additionalMetadata", required=false)  String additionalMetadata,
-        @ApiParam(value = "file detail") @RequestPart("file") MultipartFile file) {
+    default CompletableFuture<ResponseEntity<ModelApiResponse>> uploadFile(@ApiParam(value = "ID of pet to update",required=true ) @PathVariable("petId") Long petId,@ApiParam(value = "Additional data to pass to server" ) @RequestPart(value="additionalMetadata", required=false)  String additionalMetadata,@ApiParam(value = "file detail") @RequestPart("file") MultipartFile file) {
         // do some magic!
-        return () -> new ResponseEntity<ModelApiResponse>(HttpStatus.OK);
+        return CompletableFuture.completedFuture(new ResponseEntity<ModelApiResponse>(HttpStatus.OK));
     }
 
 }
diff --git a/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/api/StoreApi.java b/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/api/StoreApi.java
index 763342b3227..05d94900cd5 100644
--- a/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/api/StoreApi.java
+++ b/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/api/StoreApi.java
@@ -16,7 +16,7 @@ import org.springframework.web.bind.annotation.RequestPart;
 import org.springframework.web.multipart.MultipartFile;
 
 import java.util.List;
-import java.util.concurrent.Callable;
+import java.util.concurrent.CompletableFuture;
 
 
 @Api(value = "store", description = "the store API")
@@ -29,9 +29,9 @@ public interface StoreApi {
     @RequestMapping(value = "/store/order/{orderId}",
         produces = { "application/xml", "application/json" }, 
         method = RequestMethod.DELETE)
-    default Callable<ResponseEntity<Void>> deleteOrder(@ApiParam(value = "ID of the order that needs to be deleted",required=true ) @PathVariable("orderId") String orderId) {
+    default CompletableFuture<ResponseEntity<Void>> deleteOrder(@ApiParam(value = "ID of the order that needs to be deleted",required=true ) @PathVariable("orderId") String orderId) {
         // do some magic!
-        return () -> new ResponseEntity<Void>(HttpStatus.OK);
+        return CompletableFuture.completedFuture(new ResponseEntity<Void>(HttpStatus.OK));
     }
 
 
@@ -43,9 +43,9 @@ public interface StoreApi {
     @RequestMapping(value = "/store/inventory",
         produces = { "application/json" }, 
         method = RequestMethod.GET)
-    default Callable<ResponseEntity<Map<String, Integer>>> getInventory() {
+    default CompletableFuture<ResponseEntity<Map<String, Integer>>> getInventory() {
         // do some magic!
-        return () -> new ResponseEntity<Map<String, Integer>>(HttpStatus.OK);
+        return CompletableFuture.completedFuture(new ResponseEntity<Map<String, Integer>>(HttpStatus.OK));
     }
 
 
@@ -57,9 +57,9 @@ public interface StoreApi {
     @RequestMapping(value = "/store/order/{orderId}",
         produces = { "application/xml", "application/json" }, 
         method = RequestMethod.GET)
-    default Callable<ResponseEntity<Order>> getOrderById(@ApiParam(value = "ID of pet that needs to be fetched",required=true ) @PathVariable("orderId") Long orderId) {
+    default CompletableFuture<ResponseEntity<Order>> getOrderById(@ApiParam(value = "ID of pet that needs to be fetched",required=true ) @PathVariable("orderId") Long orderId) {
         // do some magic!
-        return () -> new ResponseEntity<Order>(HttpStatus.OK);
+        return CompletableFuture.completedFuture(new ResponseEntity<Order>(HttpStatus.OK));
     }
 
 
@@ -70,9 +70,9 @@ public interface StoreApi {
     @RequestMapping(value = "/store/order",
         produces = { "application/xml", "application/json" }, 
         method = RequestMethod.POST)
-    default Callable<ResponseEntity<Order>> placeOrder(@ApiParam(value = "order placed for purchasing the pet" ,required=true ) @RequestBody Order body) {
+    default CompletableFuture<ResponseEntity<Order>> placeOrder(@ApiParam(value = "order placed for purchasing the pet" ,required=true ) @RequestBody Order body) {
         // do some magic!
-        return () -> new ResponseEntity<Order>(HttpStatus.OK);
+        return CompletableFuture.completedFuture(new ResponseEntity<Order>(HttpStatus.OK));
     }
 
 }
diff --git a/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/api/UserApi.java b/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/api/UserApi.java
index 8e284d5b8f4..4badb1ac87c 100644
--- a/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/api/UserApi.java
+++ b/samples/server/petstore/spring-mvc-j8-async/src/main/java/io/swagger/api/UserApi.java
@@ -16,7 +16,7 @@ import org.springframework.web.bind.annotation.RequestPart;
 import org.springframework.web.multipart.MultipartFile;
 
 import java.util.List;
-import java.util.concurrent.Callable;
+import java.util.concurrent.CompletableFuture;
 
 
 @Api(value = "user", description = "the user API")
@@ -28,9 +28,9 @@ public interface UserApi {
     @RequestMapping(value = "/user",
         produces = { "application/xml", "application/json" }, 
         method = RequestMethod.POST)
-    default Callable<ResponseEntity<Void>> createUser(@ApiParam(value = "Created user object" ,required=true ) @RequestBody User body) {
+    default CompletableFuture<ResponseEntity<Void>> createUser(@ApiParam(value = "Created user object" ,required=true ) @RequestBody User body) {
         // do some magic!
-        return () -> new ResponseEntity<Void>(HttpStatus.OK);
+        return CompletableFuture.completedFuture(new ResponseEntity<Void>(HttpStatus.OK));
     }
 
 
@@ -40,9 +40,9 @@ public interface UserApi {
     @RequestMapping(value = "/user/createWithArray",
         produces = { "application/xml", "application/json" }, 
         method = RequestMethod.POST)
-    default Callable<ResponseEntity<Void>> createUsersWithArrayInput(@ApiParam(value = "List of user object" ,required=true ) @RequestBody List<User> body) {
+    default CompletableFuture<ResponseEntity<Void>> createUsersWithArrayInput(@ApiParam(value = "List of user object" ,required=true ) @RequestBody List<User> body) {
         // do some magic!
-        return () -> new ResponseEntity<Void>(HttpStatus.OK);
+        return CompletableFuture.completedFuture(new ResponseEntity<Void>(HttpStatus.OK));
     }
 
 
@@ -52,9 +52,9 @@ public interface UserApi {
     @RequestMapping(value = "/user/createWithList",
         produces = { "application/xml", "application/json" }, 
         method = RequestMethod.POST)
-    default Callable<ResponseEntity<Void>> createUsersWithListInput(@ApiParam(value = "List of user object" ,required=true ) @RequestBody List<User> body) {
+    default CompletableFuture<ResponseEntity<Void>> createUsersWithListInput(@ApiParam(value = "List of user object" ,required=true ) @RequestBody List<User> body) {
         // do some magic!
-        return () -> new ResponseEntity<Void>(HttpStatus.OK);
+        return CompletableFuture.completedFuture(new ResponseEntity<Void>(HttpStatus.OK));
     }
 
 
@@ -65,9 +65,9 @@ public interface UserApi {
     @RequestMapping(value = "/user/{username}",
         produces = { "application/xml", "application/json" }, 
         method = RequestMethod.DELETE)
-    default Callable<ResponseEntity<Void>> deleteUser(@ApiParam(value = "The name that needs to be deleted",required=true ) @PathVariable("username") String username) {
+    default CompletableFuture<ResponseEntity<Void>> deleteUser(@ApiParam(value = "The name that needs to be deleted",required=true ) @PathVariable("username") String username) {
         // do some magic!
-        return () -> new ResponseEntity<Void>(HttpStatus.OK);
+        return CompletableFuture.completedFuture(new ResponseEntity<Void>(HttpStatus.OK));
     }
 
 
@@ -79,9 +79,9 @@ public interface UserApi {
     @RequestMapping(value = "/user/{username}",
         produces = { "application/xml", "application/json" }, 
         method = RequestMethod.GET)
-    default Callable<ResponseEntity<User>> getUserByName(@ApiParam(value = "The name that needs to be fetched. Use user1 for testing. ",required=true ) @PathVariable("username") String username) {
+    default CompletableFuture<ResponseEntity<User>> getUserByName(@ApiParam(value = "The name that needs to be fetched. Use user1 for testing. ",required=true ) @PathVariable("username") String username) {
         // do some magic!
-        return () -> new ResponseEntity<User>(HttpStatus.OK);
+        return CompletableFuture.completedFuture(new ResponseEntity<User>(HttpStatus.OK));
     }
 
 
@@ -92,10 +92,9 @@ public interface UserApi {
     @RequestMapping(value = "/user/login",
         produces = { "application/xml", "application/json" }, 
         method = RequestMethod.GET)
-    default Callable<ResponseEntity<String>> loginUser(@ApiParam(value = "The user name for login", required = true) @RequestParam(value = "username", required = true) String username,
-        @ApiParam(value = "The password for login in clear text", required = true) @RequestParam(value = "password", required = true) String password) {
+    default CompletableFuture<ResponseEntity<String>> loginUser(@ApiParam(value = "The user name for login", required = true) @RequestParam(value = "username", required = true) String username,@ApiParam(value = "The password for login in clear text", required = true) @RequestParam(value = "password", required = true) String password) {
         // do some magic!
-        return () -> new ResponseEntity<String>(HttpStatus.OK);
+        return CompletableFuture.completedFuture(new ResponseEntity<String>(HttpStatus.OK));
     }
 
 
@@ -105,9 +104,9 @@ public interface UserApi {
     @RequestMapping(value = "/user/logout",
         produces = { "application/xml", "application/json" }, 
         method = RequestMethod.GET)
-    default Callable<ResponseEntity<Void>> logoutUser() {
+    default CompletableFuture<ResponseEntity<Void>> logoutUser() {
         // do some magic!
-        return () -> new ResponseEntity<Void>(HttpStatus.OK);
+        return CompletableFuture.completedFuture(new ResponseEntity<Void>(HttpStatus.OK));
     }
 
 
@@ -118,10 +117,9 @@ public interface UserApi {
     @RequestMapping(value = "/user/{username}",
         produces = { "application/xml", "application/json" }, 
         method = RequestMethod.PUT)
-    default Callable<ResponseEntity<Void>> updateUser(@ApiParam(value = "name that need to be deleted",required=true ) @PathVariable("username") String username,
-        @ApiParam(value = "Updated user object" ,required=true ) @RequestBody User body) {
+    default CompletableFuture<ResponseEntity<Void>> updateUser(@ApiParam(value = "name that need to be deleted",required=true ) @PathVariable("username") String username,@ApiParam(value = "Updated user object" ,required=true ) @RequestBody User body) {
         // do some magic!
-        return () -> new ResponseEntity<Void>(HttpStatus.OK);
+        return CompletableFuture.completedFuture(new ResponseEntity<Void>(HttpStatus.OK));
     }
 
 }