[Java] Threetenbp dates support (#4029)

* [feign] add threetenbp support for feign clients

* [okhttp] add threetenbp support for okhttp clients

* [jersey] add threetenbp support for jersey clients

* [retrofit2] add threetenbp support for retrofit2 clients

* [spring] add threetenbp support for spring generators

* add a workaround in tests for a bug in the petstore

The petstore doesn't manage fractional digits of dates correctly when there are less than 3

samples/client/petstore/java/jersey2-java8/docs/FakeApi.md

@@ -54,7 +54,7 @@ No authorization required
 
 <a name="testEndpointParameters"></a>
 # **testEndpointParameters**
-> testEndpointParameters(number, _double, patternWithoutDelimiter, _byte, integer, int32, int64, _float, string, binary, date, dateTime, password)
+> testEndpointParameters(number, _double, patternWithoutDelimiter, _byte, integer, int32, int64, _float, string, binary, date, dateTime, password, paramCallback)
 
 Fake endpoint for testing various parameters 假端點 偽のエンドポイント 가짜 엔드 포인트 
 
@@ -90,8 +90,9 @@ byte[] binary = B; // byte[] | None
 LocalDate date = new LocalDate(); // LocalDate | None
 OffsetDateTime dateTime = new OffsetDateTime(); // OffsetDateTime | None
 String password = "password_example"; // String | None
+String paramCallback = "paramCallback_example"; // String | None
 try {
-    apiInstance.testEndpointParameters(number, _double, patternWithoutDelimiter, _byte, integer, int32, int64, _float, string, binary, date, dateTime, password);
+    apiInstance.testEndpointParameters(number, _double, patternWithoutDelimiter, _byte, integer, int32, int64, _float, string, binary, date, dateTime, password, paramCallback);
 } catch (ApiException e) {
     System.err.println("Exception when calling FakeApi#testEndpointParameters");
     e.printStackTrace();
@@ -115,6 +116,7 @@ Name | Type | Description  | Notes
  **date** | **LocalDate**| None | [optional]
  **dateTime** | **OffsetDateTime**| None | [optional]
  **password** | **String**| None | [optional]
+ **paramCallback** | **String**| None | [optional]
 
 ### Return type
 

samples/client/petstore/java/jersey2-java8/docs/FakeclassnametagsApi.md

@@ -0,0 +1,52 @@
+# FakeclassnametagsApi
+
+All URIs are relative to *http://petstore.swagger.io/v2*
+
+Method | HTTP request | Description
+------------- | ------------- | -------------
+[**testClassname**](FakeclassnametagsApi.md#testClassname) | **PATCH** /fake_classname_test | To test class name in snake case
+
+
+<a name="testClassname"></a>
+# **testClassname**
+> Client testClassname(body)
+
+To test class name in snake case
+
+### Example
+```java
+// Import classes:
+//import io.swagger.client.ApiException;
+//import io.swagger.client.api.FakeclassnametagsApi;
+
+
+FakeclassnametagsApi apiInstance = new FakeclassnametagsApi();
+Client body = new Client(); // Client | client model
+try {
+    Client result = apiInstance.testClassname(body);
+    System.out.println(result);
+} catch (ApiException e) {
+    System.err.println("Exception when calling FakeclassnametagsApi#testClassname");
+    e.printStackTrace();
+}
+```
+
+### Parameters
+
+Name | Type | Description  | Notes
+------------- | ------------- | ------------- | -------------
+ **body** | [**Client**](Client.md)| client model |
+
+### Return type
+
+[**Client**](Client.md)
+
+### Authorization
+
+No authorization required
+
+### HTTP request headers
+
+ - **Content-Type**: application/json
+ - **Accept**: application/json
+