diff --git a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/ApiClient.java b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/ApiClient.java
index 9de69dde1e8..d1a5c2102a8 100644
--- a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/ApiClient.java
+++ b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/ApiClient.java
@@ -2,6 +2,7 @@
 
 import com.google.gson.Gson;
 import com.google.gson.JsonParseException;
+import com.google.gson.JsonElement;
 import okhttp3.Interceptor;
 import okhttp3.OkHttpClient;
 import okhttp3.RequestBody;
@@ -25,6 +26,7 @@
 import java.text.DateFormat;
 import java.util.LinkedHashMap;
 import java.util.Map;
+import java.util.HashMap;
 
 public class ApiClient {
 
diff --git a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/JSON.java b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/JSON.java
index 590495331b6..9fadecfb138 100644
--- a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/JSON.java
+++ b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/JSON.java
@@ -20,10 +20,15 @@
 import com.google.gson.internal.bind.util.ISO8601Utils;
 import com.google.gson.stream.JsonReader;
 import com.google.gson.stream.JsonWriter;
+import com.google.gson.JsonElement;
+import io.gsonfire.GsonFireBuilder;
+import io.gsonfire.TypeSelector;
 import org.threeten.bp.LocalDate;
 import org.threeten.bp.OffsetDateTime;
 import org.threeten.bp.format.DateTimeFormatter;
 
+import io.swagger.client.model.*;
+
 import java.io.IOException;
 import java.io.StringReader;
 import java.lang.reflect.Type;
@@ -31,6 +36,8 @@
 import java.text.ParseException;
 import java.text.ParsePosition;
 import java.util.Date;
+import java.util.Map;
+import java.util.HashMap;
 
 public class JSON {
     private Gson gson;
@@ -39,8 +46,25 @@ public class JSON {
     private OffsetDateTimeTypeAdapter offsetDateTimeTypeAdapter = new OffsetDateTimeTypeAdapter();
     private LocalDateTypeAdapter localDateTypeAdapter = new LocalDateTypeAdapter();
 
+    public static GsonBuilder createGson() {
+        GsonFireBuilder fireBuilder = new GsonFireBuilder()
+          .registerTypeSelector(Animal.class, new TypeSelector() {
+            @Override
+            public Class getClassForElement(JsonElement readElement) {
+                Map classByDiscriminatorValue = new HashMap();
+                classByDiscriminatorValue.put("Cat".toUpperCase(), Cat.class);
+                classByDiscriminatorValue.put("Dog".toUpperCase(), Dog.class);
+                String discriminatorField = "className";
+                String discriminatorValue = readElement.getAsJsonObject().get(discriminatorField).getAsString();
+                return (Class) classByDiscriminatorValue.get(discriminatorValue.toUpperCase());
+            }
+          })
+        ;
+        return fireBuilder.createGsonBuilder();
+    }
+
     public JSON() {
-        gson = new GsonBuilder()
+        gson = createGson()
             .registerTypeAdapter(Date.class, dateTypeAdapter)
             .registerTypeAdapter(java.sql.Date.class, sqlDateTypeAdapter)
             .registerTypeAdapter(OffsetDateTime.class, offsetDateTimeTypeAdapter)
diff --git a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/api/FakeApi.java b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/api/FakeApi.java
index 70293f5985b..d169b8111b7 100644
--- a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/api/FakeApi.java
+++ b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/api/FakeApi.java
@@ -6,6 +6,7 @@
 import retrofit2.http.*;
 
 import okhttp3.RequestBody;
+import okhttp3.ResponseBody;
 
 import java.math.BigDecimal;
 import io.swagger.client.model.Client;
diff --git a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/api/FakeClassnameTags123Api.java b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/api/FakeClassnameTags123Api.java
index 8435dbc4cd6..c31c31c9233 100644
--- a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/api/FakeClassnameTags123Api.java
+++ b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/api/FakeClassnameTags123Api.java
@@ -6,6 +6,7 @@
 import retrofit2.http.*;
 
 import okhttp3.RequestBody;
+import okhttp3.ResponseBody;
 
 import io.swagger.client.model.Client;
 
diff --git a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/api/PetApi.java b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/api/PetApi.java
index 06dff092eec..8d48189ce93 100644
--- a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/api/PetApi.java
+++ b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/api/PetApi.java
@@ -6,6 +6,7 @@
 import retrofit2.http.*;
 
 import okhttp3.RequestBody;
+import okhttp3.ResponseBody;
 
 import java.io.File;
 import io.swagger.client.model.ModelApiResponse;
diff --git a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/api/StoreApi.java b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/api/StoreApi.java
index 0795776d1fb..99367e1a0c3 100644
--- a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/api/StoreApi.java
+++ b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/api/StoreApi.java
@@ -6,6 +6,7 @@
 import retrofit2.http.*;
 
 import okhttp3.RequestBody;
+import okhttp3.ResponseBody;
 
 import io.swagger.client.model.Order;
 
diff --git a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/api/UserApi.java b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/api/UserApi.java
index 8610a28e3a6..ab2074c4e80 100644
--- a/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/api/UserApi.java
+++ b/samples/client/petstore/java/retrofit2/src/main/java/io/swagger/client/api/UserApi.java
@@ -6,6 +6,7 @@
 import retrofit2.http.*;
 
 import okhttp3.RequestBody;
+import okhttp3.ResponseBody;
 
 import io.swagger.client.model.User;