diff --git a/modules/openapi-generator/src/main/resources/Java/libraries/google-api-client/api.mustache b/modules/openapi-generator/src/main/resources/Java/libraries/google-api-client/api.mustache
index 757ee73e9261..2b4365bbfa2a 100644
--- a/modules/openapi-generator/src/main/resources/Java/libraries/google-api-client/api.mustache
+++ b/modules/openapi-generator/src/main/resources/Java/libraries/google-api-client/api.mustache
@@ -123,7 +123,13 @@ public class {{classname}} {
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = {{#isBodyAllowed}}{{#bodyParam}}apiClient.new JacksonJsonHttpContent({{paramName}}){{/bodyParam}}{{^bodyParam}}new EmptyContent(){{/bodyParam}}{{/isBodyAllowed}}{{^isBodyAllowed}}null{{/isBodyAllowed}};
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.{{httpMethod}}, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.{{httpMethod}}, genericUrl, content);
+        {{#headerParams}}
+        if ({{paramName}} != null) {
+            httpRequest.getHeaders().set("{{baseName}}", {{paramName}});
+        }
+        {{/headerParams}}
+        return httpRequest.execute();
     }{{#bodyParam}}
 
       {{#isDeprecated}}
@@ -159,7 +165,13 @@ public class {{classname}} {
               HttpContent content = {{#bodyParam}}{{paramName}} == null ?
                 apiClient.new JacksonJsonHttpContent(null) :
                 new InputStreamContent(mediaType == null ? Json.MEDIA_TYPE : mediaType, {{paramName}}){{/bodyParam}};
-              return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.{{httpMethod}}, genericUrl, content).execute();
+              com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.{{httpMethod}}, genericUrl, content);
+              {{#headerParams}}
+              if ({{paramName}} != null) {
+                  httpRequest.getHeaders().set("{{baseName}}", {{paramName}});
+              }
+              {{/headerParams}}
+              return httpRequest.execute();
       }{{/bodyParam}}
 
     {{#isDeprecated}}
@@ -201,7 +213,21 @@ public class {{classname}} {
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = {{#isBodyAllowed}}{{#bodyParam}}apiClient.new JacksonJsonHttpContent({{paramName}}){{/bodyParam}}{{^bodyParam}}new EmptyContent(){{/bodyParam}}{{/isBodyAllowed}}{{^isBodyAllowed}}null{{/isBodyAllowed}};
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.{{httpMethod}}, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.{{httpMethod}}, genericUrl, content);
+        {{#hasHeaderParams}}
+        // Note: Header params passed via 'params' map are handled below
+        for (Map.Entry<String, Object> entry: params.entrySet()) {
+            String key = entry.getKey();
+            Object value = entry.getValue();
+            // Check if this is a header parameter by name
+            {{#headerParams}}
+            if ("{{baseName}}".equals(key) && value != null) {
+                httpRequest.getHeaders().set(key, value);
+            }
+            {{/headerParams}}
+        }
+        {{/hasHeaderParams}}
+        return httpRequest.execute();
     }
 
 
diff --git a/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/api/AnotherFakeApi.java b/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
index 89f412c47760..22f651ee1550 100644
--- a/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
+++ b/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
@@ -87,7 +87,11 @@ public HttpResponse call123testSpecialTagsForHttpResponse(@javax.annotation.Nonn
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PATCH, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PATCH, genericUrl, content);
+        if (uuidTest != null) {
+            httpRequest.getHeaders().set("uuid_test", uuidTest);
+        }
+        return httpRequest.execute();
     }
 
       public HttpResponse call123testSpecialTagsForHttpResponse(@javax.annotation.Nonnull UUID uuidTest, java.io.InputStream body, String mediaType) throws IOException {
@@ -106,7 +110,11 @@ public HttpResponse call123testSpecialTagsForHttpResponse(@javax.annotation.Nonn
               HttpContent content = body == null ?
                 apiClient.new JacksonJsonHttpContent(null) :
                 new InputStreamContent(mediaType == null ? Json.MEDIA_TYPE : mediaType, body);
-              return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PATCH, genericUrl, content).execute();
+              com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PATCH, genericUrl, content);
+              if (uuidTest != null) {
+                  httpRequest.getHeaders().set("uuid_test", uuidTest);
+              }
+              return httpRequest.execute();
       }
 
     public HttpResponse call123testSpecialTagsForHttpResponse(@javax.annotation.Nonnull UUID uuidTest, @javax.annotation.Nonnull Client body, Map<String, Object> params) throws IOException {
@@ -141,7 +149,17 @@ public HttpResponse call123testSpecialTagsForHttpResponse(@javax.annotation.Nonn
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PATCH, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PATCH, genericUrl, content);
+        // Note: Header params passed via 'params' map are handled below
+        for (Map.Entry<String, Object> entry: params.entrySet()) {
+            String key = entry.getKey();
+            Object value = entry.getValue();
+            // Check if this is a header parameter by name
+            if ("uuid_test".equals(key) && value != null) {
+                httpRequest.getHeaders().set(key, value);
+            }
+        }
+        return httpRequest.execute();
     }
 
 
diff --git a/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/api/FakeApi.java b/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/api/FakeApi.java
index a3061d476aae..7ac7c4d4172a 100644
--- a/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/api/FakeApi.java
+++ b/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/api/FakeApi.java
@@ -83,7 +83,8 @@ public HttpResponse createXmlItemForHttpResponse(@javax.annotation.Nonnull XmlIt
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(xmlItem);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
       public HttpResponse createXmlItemForHttpResponse(java.io.InputStream xmlItem, String mediaType) throws IOException {
@@ -99,7 +100,8 @@ public HttpResponse createXmlItemForHttpResponse(java.io.InputStream xmlItem, St
               HttpContent content = xmlItem == null ?
                 apiClient.new JacksonJsonHttpContent(null) :
                 new InputStreamContent(mediaType == null ? Json.MEDIA_TYPE : mediaType, xmlItem);
-              return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+              com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+              return httpRequest.execute();
       }
 
     public HttpResponse createXmlItemForHttpResponse(@javax.annotation.Nonnull XmlItem xmlItem, Map<String, Object> params) throws IOException {
@@ -131,7 +133,8 @@ public HttpResponse createXmlItemForHttpResponse(@javax.annotation.Nonnull XmlIt
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(xmlItem);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
@@ -169,7 +172,8 @@ public HttpResponse fakeOuterBooleanSerializeForHttpResponse(@javax.annotation.N
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
       public HttpResponse fakeOuterBooleanSerializeForHttpResponse(java.io.InputStream body, String mediaType) throws IOException {
@@ -182,7 +186,8 @@ public HttpResponse fakeOuterBooleanSerializeForHttpResponse(java.io.InputStream
               HttpContent content = body == null ?
                 apiClient.new JacksonJsonHttpContent(null) :
                 new InputStreamContent(mediaType == null ? Json.MEDIA_TYPE : mediaType, body);
-              return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+              com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+              return httpRequest.execute();
       }
 
     public HttpResponse fakeOuterBooleanSerializeForHttpResponse(@javax.annotation.Nullable Boolean body, Map<String, Object> params) throws IOException {
@@ -211,7 +216,8 @@ public HttpResponse fakeOuterBooleanSerializeForHttpResponse(@javax.annotation.N
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
@@ -249,7 +255,8 @@ public HttpResponse fakeOuterCompositeSerializeForHttpResponse(@javax.annotation
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
       public HttpResponse fakeOuterCompositeSerializeForHttpResponse(java.io.InputStream body, String mediaType) throws IOException {
@@ -262,7 +269,8 @@ public HttpResponse fakeOuterCompositeSerializeForHttpResponse(java.io.InputStre
               HttpContent content = body == null ?
                 apiClient.new JacksonJsonHttpContent(null) :
                 new InputStreamContent(mediaType == null ? Json.MEDIA_TYPE : mediaType, body);
-              return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+              com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+              return httpRequest.execute();
       }
 
     public HttpResponse fakeOuterCompositeSerializeForHttpResponse(@javax.annotation.Nullable OuterComposite body, Map<String, Object> params) throws IOException {
@@ -291,7 +299,8 @@ public HttpResponse fakeOuterCompositeSerializeForHttpResponse(@javax.annotation
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
@@ -329,7 +338,8 @@ public HttpResponse fakeOuterNumberSerializeForHttpResponse(@javax.annotation.Nu
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
       public HttpResponse fakeOuterNumberSerializeForHttpResponse(java.io.InputStream body, String mediaType) throws IOException {
@@ -342,7 +352,8 @@ public HttpResponse fakeOuterNumberSerializeForHttpResponse(java.io.InputStream
               HttpContent content = body == null ?
                 apiClient.new JacksonJsonHttpContent(null) :
                 new InputStreamContent(mediaType == null ? Json.MEDIA_TYPE : mediaType, body);
-              return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+              com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+              return httpRequest.execute();
       }
 
     public HttpResponse fakeOuterNumberSerializeForHttpResponse(@javax.annotation.Nullable BigDecimal body, Map<String, Object> params) throws IOException {
@@ -371,7 +382,8 @@ public HttpResponse fakeOuterNumberSerializeForHttpResponse(@javax.annotation.Nu
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
@@ -409,7 +421,8 @@ public HttpResponse fakeOuterStringSerializeForHttpResponse(@javax.annotation.Nu
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
       public HttpResponse fakeOuterStringSerializeForHttpResponse(java.io.InputStream body, String mediaType) throws IOException {
@@ -422,7 +435,8 @@ public HttpResponse fakeOuterStringSerializeForHttpResponse(java.io.InputStream
               HttpContent content = body == null ?
                 apiClient.new JacksonJsonHttpContent(null) :
                 new InputStreamContent(mediaType == null ? Json.MEDIA_TYPE : mediaType, body);
-              return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+              com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+              return httpRequest.execute();
       }
 
     public HttpResponse fakeOuterStringSerializeForHttpResponse(@javax.annotation.Nullable String body, Map<String, Object> params) throws IOException {
@@ -451,7 +465,8 @@ public HttpResponse fakeOuterStringSerializeForHttpResponse(@javax.annotation.Nu
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
@@ -487,7 +502,8 @@ public HttpResponse testBodyWithFileSchemaForHttpResponse(@javax.annotation.Nonn
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PUT, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PUT, genericUrl, content);
+        return httpRequest.execute();
     }
 
       public HttpResponse testBodyWithFileSchemaForHttpResponse(java.io.InputStream body, String mediaType) throws IOException {
@@ -503,7 +519,8 @@ public HttpResponse testBodyWithFileSchemaForHttpResponse(java.io.InputStream bo
               HttpContent content = body == null ?
                 apiClient.new JacksonJsonHttpContent(null) :
                 new InputStreamContent(mediaType == null ? Json.MEDIA_TYPE : mediaType, body);
-              return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PUT, genericUrl, content).execute();
+              com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PUT, genericUrl, content);
+              return httpRequest.execute();
       }
 
     public HttpResponse testBodyWithFileSchemaForHttpResponse(@javax.annotation.Nonnull FileSchemaTestClass body, Map<String, Object> params) throws IOException {
@@ -535,7 +552,8 @@ public HttpResponse testBodyWithFileSchemaForHttpResponse(@javax.annotation.Nonn
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PUT, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PUT, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
@@ -585,7 +603,8 @@ public HttpResponse testBodyWithQueryParamsForHttpResponse(@javax.annotation.Non
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PUT, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PUT, genericUrl, content);
+        return httpRequest.execute();
     }
 
       public HttpResponse testBodyWithQueryParamsForHttpResponse(@javax.annotation.Nonnull String query, java.io.InputStream body, String mediaType) throws IOException {
@@ -615,7 +634,8 @@ public HttpResponse testBodyWithQueryParamsForHttpResponse(@javax.annotation.Non
               HttpContent content = body == null ?
                 apiClient.new JacksonJsonHttpContent(null) :
                 new InputStreamContent(mediaType == null ? Json.MEDIA_TYPE : mediaType, body);
-              return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PUT, genericUrl, content).execute();
+              com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PUT, genericUrl, content);
+              return httpRequest.execute();
       }
 
     public HttpResponse testBodyWithQueryParamsForHttpResponse(@javax.annotation.Nonnull String query, @javax.annotation.Nonnull User body, Map<String, Object> params) throws IOException {
@@ -652,7 +672,8 @@ public HttpResponse testBodyWithQueryParamsForHttpResponse(@javax.annotation.Non
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PUT, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PUT, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
@@ -696,7 +717,8 @@ public HttpResponse testClientModelForHttpResponse(@javax.annotation.Nonnull Cli
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PATCH, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PATCH, genericUrl, content);
+        return httpRequest.execute();
     }
 
       public HttpResponse testClientModelForHttpResponse(java.io.InputStream body, String mediaType) throws IOException {
@@ -712,7 +734,8 @@ public HttpResponse testClientModelForHttpResponse(java.io.InputStream body, Str
               HttpContent content = body == null ?
                 apiClient.new JacksonJsonHttpContent(null) :
                 new InputStreamContent(mediaType == null ? Json.MEDIA_TYPE : mediaType, body);
-              return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PATCH, genericUrl, content).execute();
+              com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PATCH, genericUrl, content);
+              return httpRequest.execute();
       }
 
     public HttpResponse testClientModelForHttpResponse(@javax.annotation.Nonnull Client body, Map<String, Object> params) throws IOException {
@@ -744,7 +767,8 @@ public HttpResponse testClientModelForHttpResponse(@javax.annotation.Nonnull Cli
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PATCH, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PATCH, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
@@ -809,7 +833,8 @@ public HttpResponse testEndpointParametersForHttpResponse(@javax.annotation.Nonn
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = new EmptyContent();
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
     public HttpResponse testEndpointParametersForHttpResponse(@javax.annotation.Nonnull BigDecimal number, @javax.annotation.Nonnull Double _double, @javax.annotation.Nonnull String patternWithoutDelimiter, @javax.annotation.Nonnull byte[] _byte, Map<String, Object> params) throws IOException {
@@ -850,7 +875,8 @@ public HttpResponse testEndpointParametersForHttpResponse(@javax.annotation.Nonn
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = new EmptyContent();
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
@@ -934,7 +960,14 @@ public HttpResponse testEnumParametersForHttpResponse(@javax.annotation.Nullable
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = null;
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content);
+        if (enumHeaderStringArray != null) {
+            httpRequest.getHeaders().set("enum_header_string_array", enumHeaderStringArray);
+        }
+        if (enumHeaderString != null) {
+            httpRequest.getHeaders().set("enum_header_string", enumHeaderString);
+        }
+        return httpRequest.execute();
     }
 
     public HttpResponse testEnumParametersForHttpResponse(Map<String, Object> params) throws IOException {
@@ -963,7 +996,20 @@ public HttpResponse testEnumParametersForHttpResponse(Map<String, Object> params
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = null;
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content);
+        // Note: Header params passed via 'params' map are handled below
+        for (Map.Entry<String, Object> entry: params.entrySet()) {
+            String key = entry.getKey();
+            Object value = entry.getValue();
+            // Check if this is a header parameter by name
+            if ("enum_header_string_array".equals(key) && value != null) {
+                httpRequest.getHeaders().set(key, value);
+            }
+            if ("enum_header_string".equals(key) && value != null) {
+                httpRequest.getHeaders().set(key, value);
+            }
+        }
+        return httpRequest.execute();
     }
 
 
@@ -1055,7 +1101,14 @@ public HttpResponse testGroupParametersForHttpResponse(@javax.annotation.Nonnull
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = null;
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.DELETE, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.DELETE, genericUrl, content);
+        if (requiredBooleanGroup != null) {
+            httpRequest.getHeaders().set("required_boolean_group", requiredBooleanGroup);
+        }
+        if (booleanGroup != null) {
+            httpRequest.getHeaders().set("boolean_group", booleanGroup);
+        }
+        return httpRequest.execute();
     }
 
     public HttpResponse testGroupParametersForHttpResponse(@javax.annotation.Nonnull Integer requiredStringGroup, @javax.annotation.Nonnull Boolean requiredBooleanGroup, @javax.annotation.Nonnull Long requiredInt64Group, Map<String, Object> params) throws IOException {
@@ -1097,7 +1150,20 @@ public HttpResponse testGroupParametersForHttpResponse(@javax.annotation.Nonnull
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = null;
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.DELETE, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.DELETE, genericUrl, content);
+        // Note: Header params passed via 'params' map are handled below
+        for (Map.Entry<String, Object> entry: params.entrySet()) {
+            String key = entry.getKey();
+            Object value = entry.getValue();
+            // Check if this is a header parameter by name
+            if ("required_boolean_group".equals(key) && value != null) {
+                httpRequest.getHeaders().set(key, value);
+            }
+            if ("boolean_group".equals(key) && value != null) {
+                httpRequest.getHeaders().set(key, value);
+            }
+        }
+        return httpRequest.execute();
     }
 
 
@@ -1133,7 +1199,8 @@ public HttpResponse testInlineAdditionalPropertiesForHttpResponse(@javax.annotat
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(param);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
       public HttpResponse testInlineAdditionalPropertiesForHttpResponse(java.io.InputStream param, String mediaType) throws IOException {
@@ -1149,7 +1216,8 @@ public HttpResponse testInlineAdditionalPropertiesForHttpResponse(java.io.InputS
               HttpContent content = param == null ?
                 apiClient.new JacksonJsonHttpContent(null) :
                 new InputStreamContent(mediaType == null ? Json.MEDIA_TYPE : mediaType, param);
-              return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+              com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+              return httpRequest.execute();
       }
 
     public HttpResponse testInlineAdditionalPropertiesForHttpResponse(@javax.annotation.Nonnull Map<String, String> param, Map<String, Object> params) throws IOException {
@@ -1181,7 +1249,8 @@ public HttpResponse testInlineAdditionalPropertiesForHttpResponse(@javax.annotat
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(param);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
@@ -1222,7 +1291,8 @@ public HttpResponse testJsonFormDataForHttpResponse(@javax.annotation.Nonnull St
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = null;
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content);
+        return httpRequest.execute();
     }
 
     public HttpResponse testJsonFormDataForHttpResponse(@javax.annotation.Nonnull String param, @javax.annotation.Nonnull String param2, Map<String, Object> params) throws IOException {
@@ -1257,7 +1327,8 @@ public HttpResponse testJsonFormDataForHttpResponse(@javax.annotation.Nonnull St
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = null;
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
@@ -1364,7 +1435,8 @@ public HttpResponse testQueryParameterCollectionFormatForHttpResponse(@javax.ann
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = new EmptyContent();
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PUT, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PUT, genericUrl, content);
+        return httpRequest.execute();
     }
 
     public HttpResponse testQueryParameterCollectionFormatForHttpResponse(@javax.annotation.Nonnull List<String> pipe, @javax.annotation.Nonnull List<String> ioutil, @javax.annotation.Nonnull List<String> http, @javax.annotation.Nonnull List<String> url, @javax.annotation.Nonnull List<String> context, Map<String, Object> params) throws IOException {
@@ -1418,7 +1490,8 @@ public HttpResponse testQueryParameterCollectionFormatForHttpResponse(@javax.ann
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = new EmptyContent();
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PUT, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PUT, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
diff --git a/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java b/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java
index 3e918fd103a4..171f8392839f 100644
--- a/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java
+++ b/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java
@@ -81,7 +81,8 @@ public HttpResponse testClassnameForHttpResponse(@javax.annotation.Nonnull Clien
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PATCH, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PATCH, genericUrl, content);
+        return httpRequest.execute();
     }
 
       public HttpResponse testClassnameForHttpResponse(java.io.InputStream body, String mediaType) throws IOException {
@@ -97,7 +98,8 @@ public HttpResponse testClassnameForHttpResponse(java.io.InputStream body, Strin
               HttpContent content = body == null ?
                 apiClient.new JacksonJsonHttpContent(null) :
                 new InputStreamContent(mediaType == null ? Json.MEDIA_TYPE : mediaType, body);
-              return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PATCH, genericUrl, content).execute();
+              com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PATCH, genericUrl, content);
+              return httpRequest.execute();
       }
 
     public HttpResponse testClassnameForHttpResponse(@javax.annotation.Nonnull Client body, Map<String, Object> params) throws IOException {
@@ -129,7 +131,8 @@ public HttpResponse testClassnameForHttpResponse(@javax.annotation.Nonnull Clien
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PATCH, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PATCH, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
diff --git a/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/api/PetApi.java b/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/api/PetApi.java
index 750d187510ed..fc749592d437 100644
--- a/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/api/PetApi.java
+++ b/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/api/PetApi.java
@@ -78,7 +78,8 @@ public HttpResponse addPetForHttpResponse(@javax.annotation.Nonnull Pet body) th
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
       public HttpResponse addPetForHttpResponse(java.io.InputStream body, String mediaType) throws IOException {
@@ -94,7 +95,8 @@ public HttpResponse addPetForHttpResponse(java.io.InputStream body, String media
               HttpContent content = body == null ?
                 apiClient.new JacksonJsonHttpContent(null) :
                 new InputStreamContent(mediaType == null ? Json.MEDIA_TYPE : mediaType, body);
-              return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+              com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+              return httpRequest.execute();
       }
 
     public HttpResponse addPetForHttpResponse(@javax.annotation.Nonnull Pet body, Map<String, Object> params) throws IOException {
@@ -126,7 +128,8 @@ public HttpResponse addPetForHttpResponse(@javax.annotation.Nonnull Pet body, Ma
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
@@ -168,7 +171,11 @@ public HttpResponse deletePetForHttpResponse(@javax.annotation.Nonnull Long petI
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = null;
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.DELETE, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.DELETE, genericUrl, content);
+        if (apiKey != null) {
+            httpRequest.getHeaders().set("api_key", apiKey);
+        }
+        return httpRequest.execute();
     }
 
     public HttpResponse deletePetForHttpResponse(@javax.annotation.Nonnull Long petId, Map<String, Object> params) throws IOException {
@@ -203,7 +210,17 @@ public HttpResponse deletePetForHttpResponse(@javax.annotation.Nonnull Long petI
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = null;
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.DELETE, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.DELETE, genericUrl, content);
+        // Note: Header params passed via 'params' map are handled below
+        for (Map.Entry<String, Object> entry: params.entrySet()) {
+            String key = entry.getKey();
+            Object value = entry.getValue();
+            // Check if this is a header parameter by name
+            if ("api_key".equals(key) && value != null) {
+                httpRequest.getHeaders().set(key, value);
+            }
+        }
+        return httpRequest.execute();
     }
 
 
@@ -260,7 +277,8 @@ public HttpResponse findPetsByStatusForHttpResponse(@javax.annotation.Nonnull Li
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = null;
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content);
+        return httpRequest.execute();
     }
 
     public HttpResponse findPetsByStatusForHttpResponse(@javax.annotation.Nonnull List<String> status, Map<String, Object> params) throws IOException {
@@ -294,7 +312,8 @@ public HttpResponse findPetsByStatusForHttpResponse(@javax.annotation.Nonnull Li
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = null;
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
@@ -358,7 +377,8 @@ public HttpResponse findPetsByTagsForHttpResponse(@javax.annotation.Nonnull Set<
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = null;
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content);
+        return httpRequest.execute();
     }
 
     @Deprecated
@@ -393,7 +413,8 @@ public HttpResponse findPetsByTagsForHttpResponse(@javax.annotation.Nonnull Set<
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = null;
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
@@ -444,7 +465,8 @@ public HttpResponse getPetByIdForHttpResponse(@javax.annotation.Nonnull Long pet
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = null;
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content);
+        return httpRequest.execute();
     }
 
     public HttpResponse getPetByIdForHttpResponse(@javax.annotation.Nonnull Long petId, Map<String, Object> params) throws IOException {
@@ -479,7 +501,8 @@ public HttpResponse getPetByIdForHttpResponse(@javax.annotation.Nonnull Long pet
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = null;
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
@@ -521,7 +544,8 @@ public HttpResponse updatePetForHttpResponse(@javax.annotation.Nonnull Pet body)
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PUT, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PUT, genericUrl, content);
+        return httpRequest.execute();
     }
 
       public HttpResponse updatePetForHttpResponse(java.io.InputStream body, String mediaType) throws IOException {
@@ -537,7 +561,8 @@ public HttpResponse updatePetForHttpResponse(java.io.InputStream body, String me
               HttpContent content = body == null ?
                 apiClient.new JacksonJsonHttpContent(null) :
                 new InputStreamContent(mediaType == null ? Json.MEDIA_TYPE : mediaType, body);
-              return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PUT, genericUrl, content).execute();
+              com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PUT, genericUrl, content);
+              return httpRequest.execute();
       }
 
     public HttpResponse updatePetForHttpResponse(@javax.annotation.Nonnull Pet body, Map<String, Object> params) throws IOException {
@@ -569,7 +594,8 @@ public HttpResponse updatePetForHttpResponse(@javax.annotation.Nonnull Pet body,
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PUT, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PUT, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
@@ -610,7 +636,8 @@ public HttpResponse updatePetWithFormForHttpResponse(@javax.annotation.Nonnull L
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = new EmptyContent();
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
     public HttpResponse updatePetWithFormForHttpResponse(@javax.annotation.Nonnull Long petId, Map<String, Object> params) throws IOException {
@@ -645,7 +672,8 @@ public HttpResponse updatePetWithFormForHttpResponse(@javax.annotation.Nonnull L
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = new EmptyContent();
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
@@ -692,7 +720,8 @@ public HttpResponse uploadFileForHttpResponse(@javax.annotation.Nonnull Long pet
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = new EmptyContent();
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
     public HttpResponse uploadFileForHttpResponse(@javax.annotation.Nonnull Long petId, Map<String, Object> params) throws IOException {
@@ -727,7 +756,8 @@ public HttpResponse uploadFileForHttpResponse(@javax.annotation.Nonnull Long pet
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = new EmptyContent();
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
@@ -778,7 +808,8 @@ public HttpResponse uploadFileWithRequiredFileForHttpResponse(@javax.annotation.
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = new EmptyContent();
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
     public HttpResponse uploadFileWithRequiredFileForHttpResponse(@javax.annotation.Nonnull Long petId, @javax.annotation.Nonnull File requiredFile, Map<String, Object> params) throws IOException {
@@ -816,7 +847,8 @@ public HttpResponse uploadFileWithRequiredFileForHttpResponse(@javax.annotation.
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = new EmptyContent();
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
diff --git a/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/api/StoreApi.java b/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/api/StoreApi.java
index 961d0f550a67..71f2ca5a8411 100644
--- a/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/api/StoreApi.java
+++ b/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/api/StoreApi.java
@@ -80,7 +80,8 @@ public HttpResponse deleteOrderForHttpResponse(@javax.annotation.Nonnull String
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = null;
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.DELETE, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.DELETE, genericUrl, content);
+        return httpRequest.execute();
     }
 
     public HttpResponse deleteOrderForHttpResponse(@javax.annotation.Nonnull String orderId, Map<String, Object> params) throws IOException {
@@ -115,7 +116,8 @@ public HttpResponse deleteOrderForHttpResponse(@javax.annotation.Nonnull String
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = null;
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.DELETE, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.DELETE, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
@@ -154,7 +156,8 @@ public HttpResponse getInventoryForHttpResponse() throws IOException {
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = null;
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content);
+        return httpRequest.execute();
     }
 
     public HttpResponse getInventoryForHttpResponse(Map<String, Object> params) throws IOException {
@@ -183,7 +186,8 @@ public HttpResponse getInventoryForHttpResponse(Map<String, Object> params) thro
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = null;
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
@@ -234,7 +238,8 @@ public HttpResponse getOrderByIdForHttpResponse(@javax.annotation.Nonnull Long o
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = null;
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content);
+        return httpRequest.execute();
     }
 
     public HttpResponse getOrderByIdForHttpResponse(@javax.annotation.Nonnull Long orderId, Map<String, Object> params) throws IOException {
@@ -269,7 +274,8 @@ public HttpResponse getOrderByIdForHttpResponse(@javax.annotation.Nonnull Long o
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = null;
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
@@ -313,7 +319,8 @@ public HttpResponse placeOrderForHttpResponse(@javax.annotation.Nonnull Order bo
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
       public HttpResponse placeOrderForHttpResponse(java.io.InputStream body, String mediaType) throws IOException {
@@ -329,7 +336,8 @@ public HttpResponse placeOrderForHttpResponse(java.io.InputStream body, String m
               HttpContent content = body == null ?
                 apiClient.new JacksonJsonHttpContent(null) :
                 new InputStreamContent(mediaType == null ? Json.MEDIA_TYPE : mediaType, body);
-              return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+              com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+              return httpRequest.execute();
       }
 
     public HttpResponse placeOrderForHttpResponse(@javax.annotation.Nonnull Order body, Map<String, Object> params) throws IOException {
@@ -361,7 +369,8 @@ public HttpResponse placeOrderForHttpResponse(@javax.annotation.Nonnull Order bo
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
diff --git a/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/api/UserApi.java b/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/api/UserApi.java
index c7601f126d3b..0223f9f5821a 100644
--- a/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/api/UserApi.java
+++ b/samples/client/petstore/java/google-api-client/src/main/java/org/openapitools/client/api/UserApi.java
@@ -76,7 +76,8 @@ public HttpResponse createUserForHttpResponse(@javax.annotation.Nonnull User bod
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
       public HttpResponse createUserForHttpResponse(java.io.InputStream body, String mediaType) throws IOException {
@@ -92,7 +93,8 @@ public HttpResponse createUserForHttpResponse(java.io.InputStream body, String m
               HttpContent content = body == null ?
                 apiClient.new JacksonJsonHttpContent(null) :
                 new InputStreamContent(mediaType == null ? Json.MEDIA_TYPE : mediaType, body);
-              return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+              com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+              return httpRequest.execute();
       }
 
     public HttpResponse createUserForHttpResponse(@javax.annotation.Nonnull User body, Map<String, Object> params) throws IOException {
@@ -124,7 +126,8 @@ public HttpResponse createUserForHttpResponse(@javax.annotation.Nonnull User bod
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
@@ -160,7 +163,8 @@ public HttpResponse createUsersWithArrayInputForHttpResponse(@javax.annotation.N
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
       public HttpResponse createUsersWithArrayInputForHttpResponse(java.io.InputStream body, String mediaType) throws IOException {
@@ -176,7 +180,8 @@ public HttpResponse createUsersWithArrayInputForHttpResponse(java.io.InputStream
               HttpContent content = body == null ?
                 apiClient.new JacksonJsonHttpContent(null) :
                 new InputStreamContent(mediaType == null ? Json.MEDIA_TYPE : mediaType, body);
-              return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+              com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+              return httpRequest.execute();
       }
 
     public HttpResponse createUsersWithArrayInputForHttpResponse(@javax.annotation.Nonnull List<User> body, Map<String, Object> params) throws IOException {
@@ -208,7 +213,8 @@ public HttpResponse createUsersWithArrayInputForHttpResponse(@javax.annotation.N
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
@@ -244,7 +250,8 @@ public HttpResponse createUsersWithListInputForHttpResponse(@javax.annotation.No
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
       public HttpResponse createUsersWithListInputForHttpResponse(java.io.InputStream body, String mediaType) throws IOException {
@@ -260,7 +267,8 @@ public HttpResponse createUsersWithListInputForHttpResponse(java.io.InputStream
               HttpContent content = body == null ?
                 apiClient.new JacksonJsonHttpContent(null) :
                 new InputStreamContent(mediaType == null ? Json.MEDIA_TYPE : mediaType, body);
-              return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+              com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+              return httpRequest.execute();
       }
 
     public HttpResponse createUsersWithListInputForHttpResponse(@javax.annotation.Nonnull List<User> body, Map<String, Object> params) throws IOException {
@@ -292,7 +300,8 @@ public HttpResponse createUsersWithListInputForHttpResponse(@javax.annotation.No
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.POST, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
@@ -335,7 +344,8 @@ public HttpResponse deleteUserForHttpResponse(@javax.annotation.Nonnull String u
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = null;
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.DELETE, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.DELETE, genericUrl, content);
+        return httpRequest.execute();
     }
 
     public HttpResponse deleteUserForHttpResponse(@javax.annotation.Nonnull String username, Map<String, Object> params) throws IOException {
@@ -370,7 +380,8 @@ public HttpResponse deleteUserForHttpResponse(@javax.annotation.Nonnull String u
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = null;
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.DELETE, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.DELETE, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
@@ -419,7 +430,8 @@ public HttpResponse getUserByNameForHttpResponse(@javax.annotation.Nonnull Strin
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = null;
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content);
+        return httpRequest.execute();
     }
 
     public HttpResponse getUserByNameForHttpResponse(@javax.annotation.Nonnull String username, Map<String, Object> params) throws IOException {
@@ -454,7 +466,8 @@ public HttpResponse getUserByNameForHttpResponse(@javax.annotation.Nonnull Strin
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = null;
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
@@ -524,7 +537,8 @@ public HttpResponse loginUserForHttpResponse(@javax.annotation.Nonnull String us
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = null;
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content);
+        return httpRequest.execute();
     }
 
     public HttpResponse loginUserForHttpResponse(@javax.annotation.Nonnull String username, @javax.annotation.Nonnull String password, Map<String, Object> params) throws IOException {
@@ -563,7 +577,8 @@ public HttpResponse loginUserForHttpResponse(@javax.annotation.Nonnull String us
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = null;
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
@@ -594,7 +609,8 @@ public HttpResponse logoutUserForHttpResponse() throws IOException {
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = null;
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content);
+        return httpRequest.execute();
     }
 
     public HttpResponse logoutUserForHttpResponse(Map<String, Object> params) throws IOException {
@@ -623,7 +639,8 @@ public HttpResponse logoutUserForHttpResponse(Map<String, Object> params) throws
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = null;
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.GET, genericUrl, content);
+        return httpRequest.execute();
     }
 
 
@@ -671,7 +688,8 @@ public HttpResponse updateUserForHttpResponse(@javax.annotation.Nonnull String u
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PUT, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PUT, genericUrl, content);
+        return httpRequest.execute();
     }
 
       public HttpResponse updateUserForHttpResponse(@javax.annotation.Nonnull String username, java.io.InputStream body, String mediaType) throws IOException {
@@ -693,7 +711,8 @@ public HttpResponse updateUserForHttpResponse(@javax.annotation.Nonnull String u
               HttpContent content = body == null ?
                 apiClient.new JacksonJsonHttpContent(null) :
                 new InputStreamContent(mediaType == null ? Json.MEDIA_TYPE : mediaType, body);
-              return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PUT, genericUrl, content).execute();
+              com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PUT, genericUrl, content);
+              return httpRequest.execute();
       }
 
     public HttpResponse updateUserForHttpResponse(@javax.annotation.Nonnull String username, @javax.annotation.Nonnull User body, Map<String, Object> params) throws IOException {
@@ -731,7 +750,8 @@ public HttpResponse updateUserForHttpResponse(@javax.annotation.Nonnull String u
         GenericUrl genericUrl = new GenericUrl(localVarUrl);
 
         HttpContent content = apiClient.new JacksonJsonHttpContent(body);
-        return apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PUT, genericUrl, content).execute();
+        com.google.api.client.http.HttpRequest httpRequest = apiClient.getHttpRequestFactory().buildRequest(HttpMethods.PUT, genericUrl, content);
+        return httpRequest.execute();
     }