diff --git a/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/json_serializable/api/serialize.mustache b/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/json_serializable/api/serialize.mustache
index 93aed695e980..6cfeff6703a5 100644
--- a/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/json_serializable/api/serialize.mustache
+++ b/modules/openapi-generator/src/main/resources/dart/libraries/dio/serialization/json_serializable/api/serialize.mustache
@@ -1 +1,19 @@
-{{#bodyParam}}_bodyData=jsonEncode({{{paramName}}});{{/bodyParam}}
\ No newline at end of file
+      {{#hasFormParams}}
+      {{#isMultipart}}
+      _bodyData = FormData.fromMap(<String, dynamic>{
+        {{#formParams}}
+        {{^required}}{{^isNullable}}if ({{{paramName}}} != null) {{/isNullable}}{{/required}}r'{{{baseName}}}': {{#isFile}}{{{paramName}}}{{#isArray}}.toList(){{/isArray}}{{/isFile}}{{^isFile}}{{{paramName}}}{{/isFile}},
+        {{/formParams}}
+      });
+      {{/isMultipart}}
+      {{^isMultipart}}
+      _bodyData = <String, dynamic>{
+        {{#formParams}}
+        {{^required}}{{^isNullable}}if ({{{paramName}}} != null) {{/isNullable}}{{/required}}r'{{{baseName}}}': {{{paramName}}},
+        {{/formParams}}
+      };
+      {{/isMultipart}}
+      {{/hasFormParams}}
+      {{#bodyParam}}
+      _bodyData = jsonEncode({{{paramName}}});
+      {{/bodyParam}}
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/another_fake_api.dart b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/another_fake_api.dart
index 20e0f8da9464..80243cc5957a 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/another_fake_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/another_fake_api.dart
@@ -57,7 +57,8 @@ class AnotherFakeApi {
     dynamic _bodyData;
 
     try {
-_bodyData=jsonEncode(modelClient);
+      _bodyData = jsonEncode(modelClient);
+
     } catch(error, stackTrace) {
       throw DioException(
          requestOptions: _options.compose(
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/fake_api.dart b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/fake_api.dart
index 95e28581f213..370401906dcd 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/fake_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/fake_api.dart
@@ -293,7 +293,8 @@ _responseData = rawData == null ? null : deserialize<HealthCheckResult, HealthCh
     dynamic _bodyData;
 
     try {
-_bodyData=jsonEncode(pet);
+      _bodyData = jsonEncode(pet);
+
     } catch(error, stackTrace) {
       throw DioException(
          requestOptions: _options.compose(
@@ -360,7 +361,8 @@ _bodyData=jsonEncode(pet);
     dynamic _bodyData;
 
     try {
-_bodyData=jsonEncode(body);
+      _bodyData = jsonEncode(body);
+
     } catch(error, stackTrace) {
       throw DioException(
          requestOptions: _options.compose(
@@ -450,7 +452,8 @@ _responseData = rawData == null ? null : deserialize<bool, bool>(rawData, 'bool'
     dynamic _bodyData;
 
     try {
-_bodyData=jsonEncode(outerComposite);
+      _bodyData = jsonEncode(outerComposite);
+
     } catch(error, stackTrace) {
       throw DioException(
          requestOptions: _options.compose(
@@ -540,7 +543,8 @@ _responseData = rawData == null ? null : deserialize<OuterComposite, OuterCompos
     dynamic _bodyData;
 
     try {
-_bodyData=jsonEncode(body);
+      _bodyData = jsonEncode(body);
+
     } catch(error, stackTrace) {
       throw DioException(
          requestOptions: _options.compose(
@@ -630,7 +634,8 @@ _responseData = rawData == null ? null : deserialize<num, num>(rawData, 'num', g
     dynamic _bodyData;
 
     try {
-_bodyData=jsonEncode(body);
+      _bodyData = jsonEncode(body);
+
     } catch(error, stackTrace) {
       throw DioException(
          requestOptions: _options.compose(
@@ -720,7 +725,8 @@ _responseData = rawData == null ? null : deserialize<String, String>(rawData, 'S
     dynamic _bodyData;
 
     try {
-_bodyData=jsonEncode(outerObjectWithEnumProperty);
+      _bodyData = jsonEncode(outerObjectWithEnumProperty);
+
     } catch(error, stackTrace) {
       throw DioException(
          requestOptions: _options.compose(
@@ -810,7 +816,8 @@ _responseData = rawData == null ? null : deserialize<OuterObjectWithEnumProperty
     dynamic _bodyData;
 
     try {
-_bodyData=jsonEncode(requestBody);
+      _bodyData = jsonEncode(requestBody);
+
     } catch(error, stackTrace) {
       throw DioException(
          requestOptions: _options.compose(
@@ -875,7 +882,8 @@ _bodyData=jsonEncode(requestBody);
     dynamic _bodyData;
 
     try {
-_bodyData=jsonEncode(body);
+      _bodyData = jsonEncode(body);
+
     } catch(error, stackTrace) {
       throw DioException(
          requestOptions: _options.compose(
@@ -940,7 +948,8 @@ _bodyData=jsonEncode(body);
     dynamic _bodyData;
 
     try {
-_bodyData=jsonEncode(fileSchemaTestClass);
+      _bodyData = jsonEncode(fileSchemaTestClass);
+
     } catch(error, stackTrace) {
       throw DioException(
          requestOptions: _options.compose(
@@ -1011,7 +1020,8 @@ _bodyData=jsonEncode(fileSchemaTestClass);
     dynamic _bodyData;
 
     try {
-_bodyData=jsonEncode(user);
+      _bodyData = jsonEncode(user);
+
     } catch(error, stackTrace) {
       throw DioException(
          requestOptions: _options.compose(
@@ -1078,7 +1088,8 @@ _bodyData=jsonEncode(user);
     dynamic _bodyData;
 
     try {
-_bodyData=jsonEncode(modelClient);
+      _bodyData = jsonEncode(modelClient);
+
     } catch(error, stackTrace) {
       throw DioException(
          requestOptions: _options.compose(
@@ -1200,6 +1211,22 @@ _responseData = rawData == null ? null : deserialize<ModelClient, ModelClient>(r
     dynamic _bodyData;
 
     try {
+      _bodyData = <String, dynamic>{
+        if (integer != null) r'integer': integer,
+        if (int32 != null) r'int32': int32,
+        if (int64 != null) r'int64': int64,
+        r'number': number,
+        if (float != null) r'float': float,
+        r'double': double_,
+        if (string != null) r'string': string,
+        r'pattern_without_delimiter': patternWithoutDelimiter,
+        r'byte': byte,
+        if (binary != null) r'binary': binary,
+        if (date != null) r'date': date,
+        if (dateTime != null) r'dateTime': dateTime,
+        if (password != null) r'password': password,
+        if (callback != null) r'callback': callback,
+      };
 
     } catch(error, stackTrace) {
       throw DioException(
@@ -1291,6 +1318,10 @@ _responseData = rawData == null ? null : deserialize<ModelClient, ModelClient>(r
     dynamic _bodyData;
 
     try {
+      _bodyData = <String, dynamic>{
+        if (enumFormStringArray != null) r'enum_form_string_array': enumFormStringArray,
+        if (enumFormString != null) r'enum_form_string': enumFormString,
+      };
 
     } catch(error, stackTrace) {
       throw DioException(
@@ -1431,7 +1462,8 @@ _responseData = rawData == null ? null : deserialize<ModelClient, ModelClient>(r
     dynamic _bodyData;
 
     try {
-_bodyData=jsonEncode(requestBody);
+      _bodyData = jsonEncode(requestBody);
+
     } catch(error, stackTrace) {
       throw DioException(
          requestOptions: _options.compose(
@@ -1496,7 +1528,8 @@ _bodyData=jsonEncode(requestBody);
     dynamic _bodyData;
 
     try {
-_bodyData=jsonEncode(testInlineFreeformAdditionalPropertiesRequest);
+      _bodyData = jsonEncode(testInlineFreeformAdditionalPropertiesRequest);
+
     } catch(error, stackTrace) {
       throw DioException(
          requestOptions: _options.compose(
@@ -1563,6 +1596,10 @@ _bodyData=jsonEncode(testInlineFreeformAdditionalPropertiesRequest);
     dynamic _bodyData;
 
     try {
+      _bodyData = <String, dynamic>{
+        r'param': param,
+        r'param2': param2,
+      };
 
     } catch(error, stackTrace) {
       throw DioException(
@@ -1628,7 +1665,8 @@ _bodyData=jsonEncode(testInlineFreeformAdditionalPropertiesRequest);
     dynamic _bodyData;
 
     try {
-_bodyData=jsonEncode(childWithNullable);
+      _bodyData = jsonEncode(childWithNullable);
+
     } catch(error, stackTrace) {
       throw DioException(
          requestOptions: _options.compose(
@@ -1763,7 +1801,8 @@ _bodyData=jsonEncode(childWithNullable);
     dynamic _bodyData;
 
     try {
-_bodyData=jsonEncode(requestBody);
+      _bodyData = jsonEncode(requestBody);
+
     } catch(error, stackTrace) {
       throw DioException(
          requestOptions: _options.compose(
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/fake_classname_tags123_api.dart b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/fake_classname_tags123_api.dart
index 85fbbac9287b..6fc587cd1244 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/fake_classname_tags123_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/fake_classname_tags123_api.dart
@@ -64,7 +64,8 @@ class FakeClassnameTags123Api {
     dynamic _bodyData;
 
     try {
-_bodyData=jsonEncode(modelClient);
+      _bodyData = jsonEncode(modelClient);
+
     } catch(error, stackTrace) {
       throw DioException(
          requestOptions: _options.compose(
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/pet_api.dart b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/pet_api.dart
index aab8df518913..60aaece86905 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/pet_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/pet_api.dart
@@ -63,7 +63,8 @@ class PetApi {
     dynamic _bodyData;
 
     try {
-_bodyData=jsonEncode(pet);
+      _bodyData = jsonEncode(pet);
+
     } catch(error, stackTrace) {
       throw DioException(
          requestOptions: _options.compose(
@@ -432,7 +433,8 @@ _responseData = rawData == null ? null : deserialize<Pet, Pet>(rawData, 'Pet', g
     dynamic _bodyData;
 
     try {
-_bodyData=jsonEncode(pet);
+      _bodyData = jsonEncode(pet);
+
     } catch(error, stackTrace) {
       throw DioException(
          requestOptions: _options.compose(
@@ -506,6 +508,10 @@ _bodyData=jsonEncode(pet);
     dynamic _bodyData;
 
     try {
+      _bodyData = <String, dynamic>{
+        if (name != null) r'name': name,
+        if (status != null) r'status': status,
+      };
 
     } catch(error, stackTrace) {
       throw DioException(
@@ -580,6 +586,10 @@ _bodyData=jsonEncode(pet);
     dynamic _bodyData;
 
     try {
+      _bodyData = FormData.fromMap(<String, dynamic>{
+        if (additionalMetadata != null) r'additionalMetadata': additionalMetadata,
+        if (file != null) r'file': file,
+      });
 
     } catch(error, stackTrace) {
       throw DioException(
@@ -679,6 +689,10 @@ _responseData = rawData == null ? null : deserialize<ApiResponse, ApiResponse>(r
     dynamic _bodyData;
 
     try {
+      _bodyData = FormData.fromMap(<String, dynamic>{
+        if (additionalMetadata != null) r'additionalMetadata': additionalMetadata,
+        r'requiredFile': requiredFile,
+      });
 
     } catch(error, stackTrace) {
       throw DioException(
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/store_api.dart b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/store_api.dart
index f81b521ed418..272e45a0ef6c 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/store_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/store_api.dart
@@ -253,7 +253,8 @@ _responseData = rawData == null ? null : deserialize<Order, Order>(rawData, 'Ord
     dynamic _bodyData;
 
     try {
-_bodyData=jsonEncode(order);
+      _bodyData = jsonEncode(order);
+
     } catch(error, stackTrace) {
       throw DioException(
          requestOptions: _options.compose(
diff --git a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/user_api.dart b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/user_api.dart
index 85583331abe7..87ceeccc6b4a 100644
--- a/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/user_api.dart
+++ b/samples/openapi3/client/petstore/dart-dio/petstore_client_lib_fake-json_serializable/lib/src/api/user_api.dart
@@ -57,7 +57,8 @@ class UserApi {
     dynamic _bodyData;
 
     try {
-_bodyData=jsonEncode(user);
+      _bodyData = jsonEncode(user);
+
     } catch(error, stackTrace) {
       throw DioException(
          requestOptions: _options.compose(
@@ -122,7 +123,8 @@ _bodyData=jsonEncode(user);
     dynamic _bodyData;
 
     try {
-_bodyData=jsonEncode(user);
+      _bodyData = jsonEncode(user);
+
     } catch(error, stackTrace) {
       throw DioException(
          requestOptions: _options.compose(
@@ -187,7 +189,8 @@ _bodyData=jsonEncode(user);
     dynamic _bodyData;
 
     try {
-_bodyData=jsonEncode(user);
+      _bodyData = jsonEncode(user);
+
     } catch(error, stackTrace) {
       throw DioException(
          requestOptions: _options.compose(
@@ -498,7 +501,8 @@ _responseData = rawData == null ? null : deserialize<String, String>(rawData, 'S
     dynamic _bodyData;
 
     try {
-_bodyData=jsonEncode(user);
+      _bodyData = jsonEncode(user);
+
     } catch(error, stackTrace) {
       throw DioException(
          requestOptions: _options.compose(