diff --git a/modules/openapi-generator/src/test/resources/3_0/java/petstore-with-fake-endpoints-models-for-testing-okhttp-gson.yaml b/modules/openapi-generator/src/test/resources/3_0/java/petstore-with-fake-endpoints-models-for-testing-okhttp-gson.yaml
index 0bf7e4f6684..460bb4223df 100644
--- a/modules/openapi-generator/src/test/resources/3_0/java/petstore-with-fake-endpoints-models-for-testing-okhttp-gson.yaml
+++ b/modules/openapi-generator/src/test/resources/3_0/java/petstore-with-fake-endpoints-models-for-testing-okhttp-gson.yaml
@@ -1138,6 +1138,23 @@ paths:
       responses:
         200:
           description: OK
+  /fake/parameter-string-number:
+    get:
+      tags:
+        - another_fake
+      summary: parameter string number
+      operationId: getParameterStringNumber
+      parameters:
+        - name: string_number
+          in: header 
+          description: string number
+          required: true
+          schema:
+            type: string
+            format: number
+      responses:
+        200:
+          description: OK
   /values:
     get:
       tags:
diff --git a/samples/client/petstore/java/okhttp-gson/README.md b/samples/client/petstore/java/okhttp-gson/README.md
index d582a2fceb2..6098ec22136 100644
--- a/samples/client/petstore/java/okhttp-gson/README.md
+++ b/samples/client/petstore/java/okhttp-gson/README.md
@@ -114,6 +114,7 @@ All URIs are relative to *http://petstore.swagger.io:80/v2*
 Class | Method | HTTP request | Description
 ------------ | ------------- | ------------- | -------------
 *AnotherFakeApi* | [**call123testSpecialTags**](docs/AnotherFakeApi.md#call123testSpecialTags) | **PATCH** /another-fake/dummy | To test special tags
+*AnotherFakeApi* | [**getParameterStringNumber**](docs/AnotherFakeApi.md#getParameterStringNumber) | **GET** /fake/parameter-string-number | parameter string number
 *DefaultApi* | [**fooGet**](docs/DefaultApi.md#fooGet) | **GET** /foo | 
 *FakeApi* | [**fakeHealthGet**](docs/FakeApi.md#fakeHealthGet) | **GET** /fake/health | Health check endpoint
 *FakeApi* | [**fakeOuterBooleanSerialize**](docs/FakeApi.md#fakeOuterBooleanSerialize) | **POST** /fake/outer/boolean | 
diff --git a/samples/client/petstore/java/okhttp-gson/api/openapi.yaml b/samples/client/petstore/java/okhttp-gson/api/openapi.yaml
index 45829b3ca51..9bb8dc69d5f 100644
--- a/samples/client/petstore/java/okhttp-gson/api/openapi.yaml
+++ b/samples/client/petstore/java/okhttp-gson/api/openapi.yaml
@@ -1168,6 +1168,26 @@ paths:
       tags:
       - fake
       x-accepts: application/json
+  /fake/parameter-string-number:
+    get:
+      operationId: getParameterStringNumber
+      parameters:
+      - description: string number
+        explode: false
+        in: header
+        name: string_number
+        required: true
+        schema:
+          format: number
+          type: string
+        style: simple
+      responses:
+        "200":
+          description: OK
+      summary: parameter string number
+      tags:
+      - another_fake
+      x-accepts: application/json
   /values:
     get:
       description: ""
diff --git a/samples/client/petstore/java/okhttp-gson/docs/AnotherFakeApi.md b/samples/client/petstore/java/okhttp-gson/docs/AnotherFakeApi.md
index 727c13a88e9..4ab44475b39 100644
--- a/samples/client/petstore/java/okhttp-gson/docs/AnotherFakeApi.md
+++ b/samples/client/petstore/java/okhttp-gson/docs/AnotherFakeApi.md
@@ -5,6 +5,7 @@ All URIs are relative to *http://petstore.swagger.io:80/v2*
 | Method | HTTP request | Description |
 |------------- | ------------- | -------------|
 | [**call123testSpecialTags**](AnotherFakeApi.md#call123testSpecialTags) | **PATCH** /another-fake/dummy | To test special tags |
+| [**getParameterStringNumber**](AnotherFakeApi.md#getParameterStringNumber) | **GET** /fake/parameter-string-number | parameter string number |
 
 
 <a id="call123testSpecialTags"></a>
@@ -69,3 +70,62 @@ No authorization required
 |-------------|-------------|------------------|
 | **200** | successful operation |  -  |
 
+<a id="getParameterStringNumber"></a>
+# **getParameterStringNumber**
+> getParameterStringNumber(stringNumber)
+
+parameter string number
+
+### Example
+```java
+// Import classes:
+import org.openapitools.client.ApiClient;
+import org.openapitools.client.ApiException;
+import org.openapitools.client.Configuration;
+import org.openapitools.client.models.*;
+import org.openapitools.client.api.AnotherFakeApi;
+
+public class Example {
+  public static void main(String[] args) {
+    ApiClient defaultClient = Configuration.getDefaultApiClient();
+    defaultClient.setBasePath("http://petstore.swagger.io:80/v2");
+
+    AnotherFakeApi apiInstance = new AnotherFakeApi(defaultClient);
+    BigDecimal stringNumber = new BigDecimal(78); // BigDecimal | string number
+    try {
+      apiInstance.getParameterStringNumber(stringNumber);
+    } catch (ApiException e) {
+      System.err.println("Exception when calling AnotherFakeApi#getParameterStringNumber");
+      System.err.println("Status code: " + e.getCode());
+      System.err.println("Reason: " + e.getResponseBody());
+      System.err.println("Response headers: " + e.getResponseHeaders());
+      e.printStackTrace();
+    }
+  }
+}
+```
+
+### Parameters
+
+| Name | Type | Description  | Notes |
+|------------- | ------------- | ------------- | -------------|
+| **stringNumber** | **BigDecimal**| string number | |
+
+### Return type
+
+null (empty response body)
+
+### Authorization
+
+No authorization required
+
+### HTTP request headers
+
+ - **Content-Type**: Not defined
+ - **Accept**: Not defined
+
+### HTTP response details
+| Status code | Description | Response headers |
+|-------------|-------------|------------------|
+| **200** | OK |  -  |
+
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/AnotherFakeApi.java b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
index 4eae861ab85..2711ffbb8a6 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/api/AnotherFakeApi.java
@@ -27,6 +27,7 @@ import com.google.gson.reflect.TypeToken;
 import java.io.IOException;
 
 
+import java.math.BigDecimal;
 import org.openapitools.client.model.Client;
 
 import java.lang.reflect.Type;
@@ -195,4 +196,125 @@ public class AnotherFakeApi {
         localVarApiClient.executeAsync(localVarCall, localVarReturnType, _callback);
         return localVarCall;
     }
+    /**
+     * Build call for getParameterStringNumber
+     * @param stringNumber string number (required)
+     * @param _callback Callback for upload/download progress
+     * @return Call to execute
+     * @throws ApiException If fail to serialize the request body object
+     * @http.response.details
+     <table summary="Response Details" border="1">
+        <tr><td> Status Code </td><td> Description </td><td> Response Headers </td></tr>
+        <tr><td> 200 </td><td> OK </td><td>  -  </td></tr>
+     </table>
+     */
+    public okhttp3.Call getParameterStringNumberCall(BigDecimal stringNumber, final ApiCallback _callback) throws ApiException {
+        String basePath = null;
+        // Operation Servers
+        String[] localBasePaths = new String[] {  };
+
+        // Determine Base Path to Use
+        if (localCustomBaseUrl != null){
+            basePath = localCustomBaseUrl;
+        } else if ( localBasePaths.length > 0 ) {
+            basePath = localBasePaths[localHostIndex];
+        } else {
+            basePath = null;
+        }
+
+        Object localVarPostBody = null;
+
+        // create path and map variables
+        String localVarPath = "/fake/parameter-string-number";
+
+        List<Pair> localVarQueryParams = new ArrayList<Pair>();
+        List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
+        Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+        Map<String, String> localVarCookieParams = new HashMap<String, String>();
+        Map<String, Object> localVarFormParams = new HashMap<String, Object>();
+
+        if (stringNumber != null) {
+            localVarHeaderParams.put("string_number", localVarApiClient.parameterToString(stringNumber));
+        }
+
+        final String[] localVarAccepts = {
+        };
+        final String localVarAccept = localVarApiClient.selectHeaderAccept(localVarAccepts);
+        if (localVarAccept != null) {
+            localVarHeaderParams.put("Accept", localVarAccept);
+        }
+
+        final String[] localVarContentTypes = {
+        };
+        final String localVarContentType = localVarApiClient.selectHeaderContentType(localVarContentTypes);
+        if (localVarContentType != null) {
+            localVarHeaderParams.put("Content-Type", localVarContentType);
+        }
+
+        String[] localVarAuthNames = new String[] {  };
+        return localVarApiClient.buildCall(basePath, localVarPath, "GET", localVarQueryParams, localVarCollectionQueryParams, localVarPostBody, localVarHeaderParams, localVarCookieParams, localVarFormParams, localVarAuthNames, _callback);
+    }
+
+    @SuppressWarnings("rawtypes")
+    private okhttp3.Call getParameterStringNumberValidateBeforeCall(BigDecimal stringNumber, final ApiCallback _callback) throws ApiException {
+        // verify the required parameter 'stringNumber' is set
+        if (stringNumber == null) {
+            throw new ApiException("Missing the required parameter 'stringNumber' when calling getParameterStringNumber(Async)");
+        }
+
+        return getParameterStringNumberCall(stringNumber, _callback);
+
+    }
+
+    /**
+     * parameter string number
+     * 
+     * @param stringNumber string number (required)
+     * @throws ApiException If fail to call the API, e.g. server error or cannot deserialize the response body
+     * @http.response.details
+     <table summary="Response Details" border="1">
+        <tr><td> Status Code </td><td> Description </td><td> Response Headers </td></tr>
+        <tr><td> 200 </td><td> OK </td><td>  -  </td></tr>
+     </table>
+     */
+    public void getParameterStringNumber(BigDecimal stringNumber) throws ApiException {
+        getParameterStringNumberWithHttpInfo(stringNumber);
+    }
+
+    /**
+     * parameter string number
+     * 
+     * @param stringNumber string number (required)
+     * @return ApiResponse&lt;Void&gt;
+     * @throws ApiException If fail to call the API, e.g. server error or cannot deserialize the response body
+     * @http.response.details
+     <table summary="Response Details" border="1">
+        <tr><td> Status Code </td><td> Description </td><td> Response Headers </td></tr>
+        <tr><td> 200 </td><td> OK </td><td>  -  </td></tr>
+     </table>
+     */
+    public ApiResponse<Void> getParameterStringNumberWithHttpInfo(BigDecimal stringNumber) throws ApiException {
+        okhttp3.Call localVarCall = getParameterStringNumberValidateBeforeCall(stringNumber, null);
+        return localVarApiClient.execute(localVarCall);
+    }
+
+    /**
+     * parameter string number (asynchronously)
+     * 
+     * @param stringNumber string number (required)
+     * @param _callback The callback to be executed when the API call finishes
+     * @return The request call
+     * @throws ApiException If fail to process the API call, e.g. serializing the request body object
+     * @http.response.details
+     <table summary="Response Details" border="1">
+        <tr><td> Status Code </td><td> Description </td><td> Response Headers </td></tr>
+        <tr><td> 200 </td><td> OK </td><td>  -  </td></tr>
+     </table>
+     */
+    public okhttp3.Call getParameterStringNumberAsync(BigDecimal stringNumber, final ApiCallback<Void> _callback) throws ApiException {
+
+        okhttp3.Call localVarCall = getParameterStringNumberValidateBeforeCall(stringNumber, _callback);
+        localVarApiClient.executeAsync(localVarCall, _callback);
+        return localVarCall;
+    }
 }
diff --git a/samples/client/petstore/java/okhttp-gson/src/test/java/org/openapitools/client/api/AnotherFakeApiTest.java b/samples/client/petstore/java/okhttp-gson/src/test/java/org/openapitools/client/api/AnotherFakeApiTest.java
index 0f49c5e2e01..b6162a1f3e3 100644
--- a/samples/client/petstore/java/okhttp-gson/src/test/java/org/openapitools/client/api/AnotherFakeApiTest.java
+++ b/samples/client/petstore/java/okhttp-gson/src/test/java/org/openapitools/client/api/AnotherFakeApiTest.java
@@ -2,23 +2,31 @@
  * OpenAPI Petstore
  * This spec is mainly for testing Petstore server and contains fake endpoints, models. Please do not use this for any other purpose. Special characters: \" \\
  *
- * OpenAPI spec version: 1.0.0
- *
+ * The version of the OpenAPI document: 1.0.0
+ * 
  *
  * NOTE: This class is auto generated by OpenAPI Generator (https://openapi-generator.tech).
  * https://openapi-generator.tech
  * Do not edit the class manually.
  */
 
+
 package org.openapitools.client.api;
 
-
+import org.openapitools.client.ApiException;
+import java.math.BigDecimal;
+import org.openapitools.client.model.Client;
 import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
-import org.openapitools.client.ApiException;
-import org.openapitools.client.model.Client;
 
-/** API tests for AnotherFakeApi */
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * API tests for AnotherFakeApi
+ */
 @Disabled
 public class AnotherFakeApiTest {
 
@@ -27,15 +35,27 @@ public class AnotherFakeApiTest {
     /**
      * To test special tags
      *
-     * <p>To test special tags and operation ID starting with number
+     * To test special tags and operation ID starting with number
      *
      * @throws ApiException if the Api call fails
      */
     @Test
     public void call123testSpecialTagsTest() throws ApiException {
-        Client body = null;
-        Client response = api.call123testSpecialTags(body);
-
+        Client client = null;
+        Client response = api.call123testSpecialTags(client);
         // TODO: test validations
     }
+
+    /**
+     * parameter string number
+     *
+     * @throws ApiException if the Api call fails
+     */
+    @Test
+    public void getParameterStringNumberTest() throws ApiException {
+        BigDecimal stringNumber = null;
+        api.getParameterStringNumber(stringNumber);
+        // TODO: test validations
+    }
+
 }