diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/DartDioClientCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/DartDioClientCodegen.java
index 29c81b823ce4..7a4886f5ed43 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/DartDioClientCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/DartDioClientCodegen.java
@@ -243,8 +243,6 @@ public void processOpts() {
             additionalProperties.put("core", "true");
             typeMapping.put("Date", "DateTime");
             typeMapping.put("date", "DateTime");
-            importMapping.put("DateTime", "DateTime");
-            importMapping.put("OffsetDateTime", "DateTime");
         } else if ("timemachine".equals(dateLibrary)) {
             additionalProperties.put("timeMachine", "true");
             typeMapping.put("date", "LocalDate");
diff --git a/modules/openapi-generator/src/main/resources/dart-dio/api.mustache b/modules/openapi-generator/src/main/resources/dart-dio/api.mustache
index e25eb930e83e..5b7ace703e8a 100644
--- a/modules/openapi-generator/src/main/resources/dart-dio/api.mustache
+++ b/modules/openapi-generator/src/main/resources/dart-dio/api.mustache
@@ -23,7 +23,7 @@ class {{classname}} {
         /// {{notes}}
         Future<Response{{#returnType}}<{{{returnType}}}>{{/returnType}}>{{nickname}}({{#allParams}}{{#required}}{{{dataType}}} {{paramName}},{{/required}}{{/allParams}}{ {{#allParams}}{{^required}}{{{dataType}}} {{paramName}},{{/required}}{{/allParams}}CancelToken cancelToken, Map<String, String> headers,}) async {
 
-            String path = "{{{path}}}"{{#pathParams}}.replaceAll("{" + "{{baseName}}" + "}", {{{paramName}}}.toString()){{/pathParams}};
+        String path = "{{{path}}}"{{#pathParams}}.replaceAll("{" + "{{baseName}}" + "}", {{{paramName}}}.toString()){{/pathParams}};
 
         Map<String, dynamic> queryParams = {};
         Map<String, String> headerParams = Map.from(headers ?? {});
@@ -46,7 +46,7 @@ class {{classname}} {
         {{#isMultipart}}
             {{^isFile}}
                 if ({{paramName}} != null) {
-                    formData['{{baseName}}'] = parameterToString({{paramName}});
+                    formData['{{baseName}}'] = parameterToString(_serializers, {{paramName}});
                 }
             {{/isFile}}
             {{#isFile}}
diff --git a/modules/openapi-generator/src/main/resources/dart-dio/api_util.mustache b/modules/openapi-generator/src/main/resources/dart-dio/api_util.mustache
index eedad9166fd4..e99530f6c39e 100644
--- a/modules/openapi-generator/src/main/resources/dart-dio/api_util.mustache
+++ b/modules/openapi-generator/src/main/resources/dart-dio/api_util.mustache
@@ -1,18 +1,14 @@
+import 'dart:convert';
+
+import 'package:built_value/serializer.dart';
+
 /// Format the given parameter object into string.
-String parameterToString(dynamic value) {
-  if (value == null) {
-    return '';
-  } else if (value is DateTime) {
-    return value.toUtc().toIso8601String();
-  {{#models}}
-    {{#model}}
-      {{#isEnum}}
-  } else if (value is {{classname}}) {
-    return {{classname}}TypeTransformer().encode(value).toString();
-      {{/isEnum}}
-    {{/model}}
-  {{/models}}
-  } else {
-    return value.toString();
-  }
+String parameterToString(Serializers serializers, dynamic value) {
+	if (value == null) {
+		return '';
+	} else if (value is String || value is num) {
+		return value.toString();
+	} else {
+		return json.encode(serializers.serialize(value));
+	}
 }
\ No newline at end of file
diff --git a/samples/client/petstore/dart-dio/README.md b/samples/client/petstore/dart-dio/README.md
index c9c0f49b85ed..ceda34066bc0 100644
--- a/samples/client/petstore/dart-dio/README.md
+++ b/samples/client/petstore/dart-dio/README.md
@@ -57,36 +57,36 @@ All URIs are relative to *http://petstore.swagger.io/v2*
 
 Class | Method | HTTP request | Description
 ------------ | ------------- | ------------- | -------------
-*PetApi* | [**addPet**](doc\/PetApi.md#addpet) | **post** /pet | Add a new pet to the store
-*PetApi* | [**deletePet**](doc\/PetApi.md#deletepet) | **delete** /pet/{petId} | Deletes a pet
-*PetApi* | [**findPetsByStatus**](doc\/PetApi.md#findpetsbystatus) | **get** /pet/findByStatus | Finds Pets by status
-*PetApi* | [**findPetsByTags**](doc\/PetApi.md#findpetsbytags) | **get** /pet/findByTags | Finds Pets by tags
-*PetApi* | [**getPetById**](doc\/PetApi.md#getpetbyid) | **get** /pet/{petId} | Find pet by ID
-*PetApi* | [**updatePet**](doc\/PetApi.md#updatepet) | **put** /pet | Update an existing pet
-*PetApi* | [**updatePetWithForm**](doc\/PetApi.md#updatepetwithform) | **post** /pet/{petId} | Updates a pet in the store with form data
-*PetApi* | [**uploadFile**](doc\/PetApi.md#uploadfile) | **post** /pet/{petId}/uploadImage | uploads an image
-*StoreApi* | [**deleteOrder**](doc\/StoreApi.md#deleteorder) | **delete** /store/order/{orderId} | Delete purchase order by ID
-*StoreApi* | [**getInventory**](doc\/StoreApi.md#getinventory) | **get** /store/inventory | Returns pet inventories by status
-*StoreApi* | [**getOrderById**](doc\/StoreApi.md#getorderbyid) | **get** /store/order/{orderId} | Find purchase order by ID
-*StoreApi* | [**placeOrder**](doc\/StoreApi.md#placeorder) | **post** /store/order | Place an order for a pet
-*UserApi* | [**createUser**](doc\/UserApi.md#createuser) | **post** /user | Create user
-*UserApi* | [**createUsersWithArrayInput**](doc\/UserApi.md#createuserswitharrayinput) | **post** /user/createWithArray | Creates list of users with given input array
-*UserApi* | [**createUsersWithListInput**](doc\/UserApi.md#createuserswithlistinput) | **post** /user/createWithList | Creates list of users with given input array
-*UserApi* | [**deleteUser**](doc\/UserApi.md#deleteuser) | **delete** /user/{username} | Delete user
-*UserApi* | [**getUserByName**](doc\/UserApi.md#getuserbyname) | **get** /user/{username} | Get user by user name
-*UserApi* | [**loginUser**](doc\/UserApi.md#loginuser) | **get** /user/login | Logs user into the system
-*UserApi* | [**logoutUser**](doc\/UserApi.md#logoutuser) | **get** /user/logout | Logs out current logged in user session
-*UserApi* | [**updateUser**](doc\/UserApi.md#updateuser) | **put** /user/{username} | Updated user
+*PetApi* | [**addPet**](doc//PetApi.md#addpet) | **post** /pet | Add a new pet to the store
+*PetApi* | [**deletePet**](doc//PetApi.md#deletepet) | **delete** /pet/{petId} | Deletes a pet
+*PetApi* | [**findPetsByStatus**](doc//PetApi.md#findpetsbystatus) | **get** /pet/findByStatus | Finds Pets by status
+*PetApi* | [**findPetsByTags**](doc//PetApi.md#findpetsbytags) | **get** /pet/findByTags | Finds Pets by tags
+*PetApi* | [**getPetById**](doc//PetApi.md#getpetbyid) | **get** /pet/{petId} | Find pet by ID
+*PetApi* | [**updatePet**](doc//PetApi.md#updatepet) | **put** /pet | Update an existing pet
+*PetApi* | [**updatePetWithForm**](doc//PetApi.md#updatepetwithform) | **post** /pet/{petId} | Updates a pet in the store with form data
+*PetApi* | [**uploadFile**](doc//PetApi.md#uploadfile) | **post** /pet/{petId}/uploadImage | uploads an image
+*StoreApi* | [**deleteOrder**](doc//StoreApi.md#deleteorder) | **delete** /store/order/{orderId} | Delete purchase order by ID
+*StoreApi* | [**getInventory**](doc//StoreApi.md#getinventory) | **get** /store/inventory | Returns pet inventories by status
+*StoreApi* | [**getOrderById**](doc//StoreApi.md#getorderbyid) | **get** /store/order/{orderId} | Find purchase order by ID
+*StoreApi* | [**placeOrder**](doc//StoreApi.md#placeorder) | **post** /store/order | Place an order for a pet
+*UserApi* | [**createUser**](doc//UserApi.md#createuser) | **post** /user | Create user
+*UserApi* | [**createUsersWithArrayInput**](doc//UserApi.md#createuserswitharrayinput) | **post** /user/createWithArray | Creates list of users with given input array
+*UserApi* | [**createUsersWithListInput**](doc//UserApi.md#createuserswithlistinput) | **post** /user/createWithList | Creates list of users with given input array
+*UserApi* | [**deleteUser**](doc//UserApi.md#deleteuser) | **delete** /user/{username} | Delete user
+*UserApi* | [**getUserByName**](doc//UserApi.md#getuserbyname) | **get** /user/{username} | Get user by user name
+*UserApi* | [**loginUser**](doc//UserApi.md#loginuser) | **get** /user/login | Logs user into the system
+*UserApi* | [**logoutUser**](doc//UserApi.md#logoutuser) | **get** /user/logout | Logs out current logged in user session
+*UserApi* | [**updateUser**](doc//UserApi.md#updateuser) | **put** /user/{username} | Updated user
 
 
 ## Documentation For Models
 
- - [ApiResponse](doc\/ApiResponse.md)
- - [Category](doc\/Category.md)
- - [Order](doc\/Order.md)
- - [Pet](doc\/Pet.md)
- - [Tag](doc\/Tag.md)
- - [User](doc\/User.md)
+ - [ApiResponse](doc//ApiResponse.md)
+ - [Category](doc//Category.md)
+ - [Order](doc//Order.md)
+ - [Pet](doc//Pet.md)
+ - [Tag](doc//Tag.md)
+ - [User](doc//User.md)
 
 
 ## Documentation For Authorization
diff --git a/samples/client/petstore/dart-dio/lib/api/pet_api.dart b/samples/client/petstore/dart-dio/lib/api/pet_api.dart
index 2458f5ffe927..7078df59692a 100644
--- a/samples/client/petstore/dart-dio/lib/api/pet_api.dart
+++ b/samples/client/petstore/dart-dio/lib/api/pet_api.dart
@@ -21,7 +21,7 @@ class PetApi {
         /// 
         Future<Response>addPet(Pet body,{ CancelToken cancelToken, Map<String, String> headers,}) async {
 
-            String path = "/pet";
+        String path = "/pet";
 
         Map<String, dynamic> queryParams = {};
         Map<String, String> headerParams = Map.from(headers ?? {});
@@ -54,7 +54,7 @@ class PetApi {
         /// 
         Future<Response>deletePet(int petId,{ String apiKey,CancelToken cancelToken, Map<String, String> headers,}) async {
 
-            String path = "/pet/{petId}".replaceAll("{" + "petId" + "}", petId.toString());
+        String path = "/pet/{petId}".replaceAll("{" + "petId" + "}", petId.toString());
 
         Map<String, dynamic> queryParams = {};
         Map<String, String> headerParams = Map.from(headers ?? {});
@@ -85,7 +85,7 @@ class PetApi {
         /// Multiple status values can be provided with comma separated strings
         Future<Response<List<Pet>>>findPetsByStatus(List<String> status,{ CancelToken cancelToken, Map<String, String> headers,}) async {
 
-            String path = "/pet/findByStatus";
+        String path = "/pet/findByStatus";
 
         Map<String, dynamic> queryParams = {};
         Map<String, String> headerParams = Map.from(headers ?? {});
@@ -131,7 +131,7 @@ class PetApi {
         /// Multiple tags can be provided with comma separated strings. Use tag1, tag2, tag3 for testing.
         Future<Response<List<Pet>>>findPetsByTags(List<String> tags,{ CancelToken cancelToken, Map<String, String> headers,}) async {
 
-            String path = "/pet/findByTags";
+        String path = "/pet/findByTags";
 
         Map<String, dynamic> queryParams = {};
         Map<String, String> headerParams = Map.from(headers ?? {});
@@ -177,7 +177,7 @@ class PetApi {
         /// Returns a single pet
         Future<Response<Pet>>getPetById(int petId,{ CancelToken cancelToken, Map<String, String> headers,}) async {
 
-            String path = "/pet/{petId}".replaceAll("{" + "petId" + "}", petId.toString());
+        String path = "/pet/{petId}".replaceAll("{" + "petId" + "}", petId.toString());
 
         Map<String, dynamic> queryParams = {};
         Map<String, String> headerParams = Map.from(headers ?? {});
@@ -221,7 +221,7 @@ class PetApi {
         /// 
         Future<Response>updatePet(Pet body,{ CancelToken cancelToken, Map<String, String> headers,}) async {
 
-            String path = "/pet";
+        String path = "/pet";
 
         Map<String, dynamic> queryParams = {};
         Map<String, String> headerParams = Map.from(headers ?? {});
@@ -254,7 +254,7 @@ class PetApi {
         /// 
         Future<Response>updatePetWithForm(int petId,{ String name,String status,CancelToken cancelToken, Map<String, String> headers,}) async {
 
-            String path = "/pet/{petId}".replaceAll("{" + "petId" + "}", petId.toString());
+        String path = "/pet/{petId}".replaceAll("{" + "petId" + "}", petId.toString());
 
         Map<String, dynamic> queryParams = {};
         Map<String, String> headerParams = Map.from(headers ?? {});
@@ -286,7 +286,7 @@ class PetApi {
         /// 
         Future<Response<ApiResponse>>uploadFile(int petId,{ String additionalMetadata,Uint8List file,CancelToken cancelToken, Map<String, String> headers,}) async {
 
-            String path = "/pet/{petId}/uploadImage".replaceAll("{" + "petId" + "}", petId.toString());
+        String path = "/pet/{petId}/uploadImage".replaceAll("{" + "petId" + "}", petId.toString());
 
         Map<String, dynamic> queryParams = {};
         Map<String, String> headerParams = Map.from(headers ?? {});
@@ -299,7 +299,7 @@ class PetApi {
 
         Map<String, dynamic> formData = {};
                 if (additionalMetadata != null) {
-                    formData['additionalMetadata'] = parameterToString(additionalMetadata);
+                    formData['additionalMetadata'] = parameterToString(_serializers, additionalMetadata);
                 }
                 if (file != null) {
                     formData['file'] = MultipartFile.fromBytes(file, filename: "file");
diff --git a/samples/client/petstore/dart-dio/lib/api/store_api.dart b/samples/client/petstore/dart-dio/lib/api/store_api.dart
index 8be8835b6b0f..abbe73be27c2 100644
--- a/samples/client/petstore/dart-dio/lib/api/store_api.dart
+++ b/samples/client/petstore/dart-dio/lib/api/store_api.dart
@@ -18,7 +18,7 @@ class StoreApi {
         /// For valid response try integer IDs with value &lt; 1000. Anything above 1000 or nonintegers will generate API errors
         Future<Response>deleteOrder(String orderId,{ CancelToken cancelToken, Map<String, String> headers,}) async {
 
-            String path = "/store/order/{orderId}".replaceAll("{" + "orderId" + "}", orderId.toString());
+        String path = "/store/order/{orderId}".replaceAll("{" + "orderId" + "}", orderId.toString());
 
         Map<String, dynamic> queryParams = {};
         Map<String, String> headerParams = Map.from(headers ?? {});
@@ -48,7 +48,7 @@ class StoreApi {
         /// Returns a map of status codes to quantities
         Future<Response<Map<String, int>>>getInventory({ CancelToken cancelToken, Map<String, String> headers,}) async {
 
-            String path = "/store/inventory";
+        String path = "/store/inventory";
 
         Map<String, dynamic> queryParams = {};
         Map<String, String> headerParams = Map.from(headers ?? {});
@@ -92,7 +92,7 @@ class StoreApi {
         /// For valid response try integer IDs with value &lt;&#x3D; 5 or &gt; 10. Other values will generated exceptions
         Future<Response<Order>>getOrderById(int orderId,{ CancelToken cancelToken, Map<String, String> headers,}) async {
 
-            String path = "/store/order/{orderId}".replaceAll("{" + "orderId" + "}", orderId.toString());
+        String path = "/store/order/{orderId}".replaceAll("{" + "orderId" + "}", orderId.toString());
 
         Map<String, dynamic> queryParams = {};
         Map<String, String> headerParams = Map.from(headers ?? {});
@@ -136,7 +136,7 @@ class StoreApi {
         /// 
         Future<Response<Order>>placeOrder(Order body,{ CancelToken cancelToken, Map<String, String> headers,}) async {
 
-            String path = "/store/order";
+        String path = "/store/order";
 
         Map<String, dynamic> queryParams = {};
         Map<String, String> headerParams = Map.from(headers ?? {});
diff --git a/samples/client/petstore/dart-dio/lib/api/user_api.dart b/samples/client/petstore/dart-dio/lib/api/user_api.dart
index bb2c84d2e8c4..a2d2d3189a32 100644
--- a/samples/client/petstore/dart-dio/lib/api/user_api.dart
+++ b/samples/client/petstore/dart-dio/lib/api/user_api.dart
@@ -18,7 +18,7 @@ class UserApi {
         /// This can only be done by the logged in user.
         Future<Response>createUser(User body,{ CancelToken cancelToken, Map<String, String> headers,}) async {
 
-            String path = "/user";
+        String path = "/user";
 
         Map<String, dynamic> queryParams = {};
         Map<String, String> headerParams = Map.from(headers ?? {});
@@ -51,7 +51,7 @@ class UserApi {
         /// 
         Future<Response>createUsersWithArrayInput(List<User> body,{ CancelToken cancelToken, Map<String, String> headers,}) async {
 
-            String path = "/user/createWithArray";
+        String path = "/user/createWithArray";
 
         Map<String, dynamic> queryParams = {};
         Map<String, String> headerParams = Map.from(headers ?? {});
@@ -85,7 +85,7 @@ class UserApi {
         /// 
         Future<Response>createUsersWithListInput(List<User> body,{ CancelToken cancelToken, Map<String, String> headers,}) async {
 
-            String path = "/user/createWithList";
+        String path = "/user/createWithList";
 
         Map<String, dynamic> queryParams = {};
         Map<String, String> headerParams = Map.from(headers ?? {});
@@ -119,7 +119,7 @@ class UserApi {
         /// This can only be done by the logged in user.
         Future<Response>deleteUser(String username,{ CancelToken cancelToken, Map<String, String> headers,}) async {
 
-            String path = "/user/{username}".replaceAll("{" + "username" + "}", username.toString());
+        String path = "/user/{username}".replaceAll("{" + "username" + "}", username.toString());
 
         Map<String, dynamic> queryParams = {};
         Map<String, String> headerParams = Map.from(headers ?? {});
@@ -149,7 +149,7 @@ class UserApi {
         /// 
         Future<Response<User>>getUserByName(String username,{ CancelToken cancelToken, Map<String, String> headers,}) async {
 
-            String path = "/user/{username}".replaceAll("{" + "username" + "}", username.toString());
+        String path = "/user/{username}".replaceAll("{" + "username" + "}", username.toString());
 
         Map<String, dynamic> queryParams = {};
         Map<String, String> headerParams = Map.from(headers ?? {});
@@ -193,7 +193,7 @@ class UserApi {
         /// 
         Future<Response<String>>loginUser(String username,String password,{ CancelToken cancelToken, Map<String, String> headers,}) async {
 
-            String path = "/user/login";
+        String path = "/user/login";
 
         Map<String, dynamic> queryParams = {};
         Map<String, String> headerParams = Map.from(headers ?? {});
@@ -239,7 +239,7 @@ class UserApi {
         /// 
         Future<Response>logoutUser({ CancelToken cancelToken, Map<String, String> headers,}) async {
 
-            String path = "/user/logout";
+        String path = "/user/logout";
 
         Map<String, dynamic> queryParams = {};
         Map<String, String> headerParams = Map.from(headers ?? {});
@@ -269,7 +269,7 @@ class UserApi {
         /// This can only be done by the logged in user.
         Future<Response>updateUser(String username,User body,{ CancelToken cancelToken, Map<String, String> headers,}) async {
 
-            String path = "/user/{username}".replaceAll("{" + "username" + "}", username.toString());
+        String path = "/user/{username}".replaceAll("{" + "username" + "}", username.toString());
 
         Map<String, dynamic> queryParams = {};
         Map<String, String> headerParams = Map.from(headers ?? {});
diff --git a/samples/client/petstore/dart-dio/lib/api_util.dart b/samples/client/petstore/dart-dio/lib/api_util.dart
index 3a05d24f7b99..e99530f6c39e 100644
--- a/samples/client/petstore/dart-dio/lib/api_util.dart
+++ b/samples/client/petstore/dart-dio/lib/api_util.dart
@@ -1,10 +1,14 @@
+import 'dart:convert';
+
+import 'package:built_value/serializer.dart';
+
 /// Format the given parameter object into string.
-String parameterToString(dynamic value) {
-  if (value == null) {
-    return '';
-  } else if (value is DateTime) {
-    return value.toUtc().toIso8601String();
-  } else {
-    return value.toString();
-  }
+String parameterToString(Serializers serializers, dynamic value) {
+	if (value == null) {
+		return '';
+	} else if (value is String || value is num) {
+		return value.toString();
+	} else {
+		return json.encode(serializers.serialize(value));
+	}
 }
\ No newline at end of file
diff --git a/samples/client/petstore/dart-dio/lib/model/order.dart b/samples/client/petstore/dart-dio/lib/model/order.dart
index 01f93031072e..4838d56a1d7b 100644
--- a/samples/client/petstore/dart-dio/lib/model/order.dart
+++ b/samples/client/petstore/dart-dio/lib/model/order.dart
@@ -1,4 +1,3 @@
-            import 'DateTime';
         import 'package:built_value/built_value.dart';
 import 'package:built_value/serializer.dart';