diff --git a/modules/swagger-codegen/src/main/resources/Java/ApiClient.mustache b/modules/swagger-codegen/src/main/resources/Java/ApiClient.mustache
index bfa33ac07643..d8c48e93b10e 100644
--- a/modules/swagger-codegen/src/main/resources/Java/ApiClient.mustache
+++ b/modules/swagger-codegen/src/main/resources/Java/ApiClient.mustache
@@ -22,8 +22,7 @@ import java.util.Map;
 import java.util.Map.Entry;
 import java.util.HashMap;
 import java.util.List;
-import java.util.Set;
-import java.util.HashSet;
+import java.util.ArrayList;
 import java.util.Date;
 import java.util.TimeZone;
 
@@ -243,8 +242,8 @@ public class ApiClient {
   /*
     Format to {@code Pair} objects.
   */
-  public Set<Pair> parameterToPairs(String collectionFormat, String name, Object value){
-    Set<Pair> params = new HashSet<Pair>();
+  public List<Pair> parameterToPairs(String collectionFormat, String name, Object value){
+    List<Pair> params = new ArrayList<Pair>();
 
     // preconditions
     if (name == null || name.isEmpty()) return params;
@@ -404,7 +403,7 @@ public class ApiClient {
    * @param authNames The authentications to apply
    * @return The response body in type of string
    */
-  public String invokeAPI(String path, String method, Set<Pair> queryParams, Object body, Map<String, String> headerParams, Map<String, String> formParams, String accept, String contentType, String[] authNames) throws ApiException {
+  public String invokeAPI(String path, String method, List<Pair> queryParams, Object body, Map<String, String> headerParams, Map<String, String> formParams, String accept, String contentType, String[] authNames) throws ApiException {
     updateParamsForAuth(authNames, queryParams, headerParams);
 
     Client client = getClient();
@@ -522,7 +521,7 @@ public class ApiClient {
    *
    * @param authNames The authentications to apply
    */
-  private void updateParamsForAuth(String[] authNames, Set<Pair> queryParams, Map<String, String> headerParams) {
+  private void updateParamsForAuth(String[] authNames, List<Pair> queryParams, Map<String, String> headerParams) {
     for (String authName : authNames) {
       Authentication auth = authentications.get(authName);
       if (auth == null) throw new RuntimeException("Authentication undefined: " + authName);
diff --git a/modules/swagger-codegen/src/main/resources/Java/api.mustache b/modules/swagger-codegen/src/main/resources/Java/api.mustache
index c279e4d223e8..afb28293cad7 100644
--- a/modules/swagger-codegen/src/main/resources/Java/api.mustache
+++ b/modules/swagger-codegen/src/main/resources/Java/api.mustache
@@ -62,7 +62,7 @@ public class {{classname}} {
       .replaceAll("\\{" + "{{paramName}}" + "\\}", apiClient.escapeString({{{paramName}}}.toString())){{/pathParams}};
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     Map<String, String> headerParams = new HashMap<String, String>();
     Map<String, String> formParams = new HashMap<String, String>();
 
diff --git a/modules/swagger-codegen/src/main/resources/Java/auth/ApiKeyAuth.mustache b/modules/swagger-codegen/src/main/resources/Java/auth/ApiKeyAuth.mustache
index aefbe453efdd..a1824b551ca9 100644
--- a/modules/swagger-codegen/src/main/resources/Java/auth/ApiKeyAuth.mustache
+++ b/modules/swagger-codegen/src/main/resources/Java/auth/ApiKeyAuth.mustache
@@ -3,7 +3,7 @@ package {{invokerPackage}}.auth;
 import {{invokerPackage}}.Pair;
 
 import java.util.Map;
-import java.util.Set;
+import java.util.List;
 
 public class ApiKeyAuth implements Authentication {
   private final String location;
@@ -42,7 +42,7 @@ public class ApiKeyAuth implements Authentication {
   }
 
   @Override
-  public void applyToParams(Set<Pair> queryParams, Map<String, String> headerParams) {
+  public void applyToParams(List<Pair> queryParams, Map<String, String> headerParams) {
     String value;
     if (apiKeyPrefix != null) {
       value = apiKeyPrefix + " " + apiKey;
diff --git a/modules/swagger-codegen/src/main/resources/Java/auth/Authentication.mustache b/modules/swagger-codegen/src/main/resources/Java/auth/Authentication.mustache
index 9e0b328915c6..265c74cb76f9 100644
--- a/modules/swagger-codegen/src/main/resources/Java/auth/Authentication.mustache
+++ b/modules/swagger-codegen/src/main/resources/Java/auth/Authentication.mustache
@@ -3,9 +3,9 @@ package {{invokerPackage}}.auth;
 import {{invokerPackage}}.Pair;
 
 import java.util.Map;
-import java.util.Set;
+import java.util.List;
 
 public interface Authentication {
   /** Apply authentication settings to header and query params. */
-  void applyToParams(Set<Pair> queryParams, Map<String, String> headerParams);
+  void applyToParams(List<Pair> queryParams, Map<String, String> headerParams);
 }
diff --git a/modules/swagger-codegen/src/main/resources/Java/auth/HttpBasicAuth.mustache b/modules/swagger-codegen/src/main/resources/Java/auth/HttpBasicAuth.mustache
index 73c52d96ff14..032ea57d4e89 100644
--- a/modules/swagger-codegen/src/main/resources/Java/auth/HttpBasicAuth.mustache
+++ b/modules/swagger-codegen/src/main/resources/Java/auth/HttpBasicAuth.mustache
@@ -3,7 +3,7 @@ package {{invokerPackage}}.auth;
 import {{invokerPackage}}.Pair;
 
 import java.util.Map;
-import java.util.Set;
+import java.util.List;
 
 import java.io.UnsupportedEncodingException;
 import javax.xml.bind.DatatypeConverter;
@@ -29,7 +29,7 @@ public class HttpBasicAuth implements Authentication {
   }
 
   @Override
-  public void applyToParams(Set<Pair> queryParams, Map<String, String> headerParams) {
+  public void applyToParams(List<Pair> queryParams, Map<String, String> headerParams) {
     String str = (username == null ? "" : username) + ":" + (password == null ? "" : password);
     try {
       headerParams.put("Authorization", "Basic " + DatatypeConverter.printBase64Binary(str.getBytes("UTF-8")));
diff --git a/modules/swagger-codegen/src/main/resources/Java/auth/OAuth.mustache b/modules/swagger-codegen/src/main/resources/Java/auth/OAuth.mustache
index 4de2fbed9050..66cf2ac8f0f8 100644
--- a/modules/swagger-codegen/src/main/resources/Java/auth/OAuth.mustache
+++ b/modules/swagger-codegen/src/main/resources/Java/auth/OAuth.mustache
@@ -3,11 +3,11 @@ package {{invokerPackage}}.auth;
 import {{invokerPackage}}.Pair;
 
 import java.util.Map;
-import java.util.Set;
+import java.util.List;
 
 public class OAuth implements Authentication {
   @Override
-  public void applyToParams(Set<Pair> queryParams, Map<String, String> headerParams) {
+  public void applyToParams(List<Pair> queryParams, Map<String, String> headerParams) {
     // TODO: support oauth
   }
 }
diff --git a/modules/swagger-codegen/src/main/resources/android-java/api.mustache b/modules/swagger-codegen/src/main/resources/android-java/api.mustache
index 5113116deb84..9f341301cf00 100644
--- a/modules/swagger-codegen/src/main/resources/android-java/api.mustache
+++ b/modules/swagger-codegen/src/main/resources/android-java/api.mustache
@@ -59,7 +59,7 @@ public class {{classname}} {
     String path = "{{path}}".replaceAll("\\{format\\}","json"){{#pathParams}}.replaceAll("\\{" + "{{paramName}}" + "\\}", apiInvoker.escapeString({{{paramName}}}.toString())){{/pathParams}};
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     // header params
     Map<String, String> headerParams = new HashMap<String, String>();
     // form params
diff --git a/modules/swagger-codegen/src/main/resources/android-java/apiInvoker.mustache b/modules/swagger-codegen/src/main/resources/android-java/apiInvoker.mustache
index c3bc2cd39c9d..3aeb9b8505de 100644
--- a/modules/swagger-codegen/src/main/resources/android-java/apiInvoker.mustache
+++ b/modules/swagger-codegen/src/main/resources/android-java/apiInvoker.mustache
@@ -23,8 +23,7 @@ import java.util.Collection;
 import java.util.Map;
 import java.util.HashMap;
 import java.util.List;
-import java.util.Set;
-import java.util.HashSet;
+import java.util.ArrayList;
 import java.io.IOException;
 import java.io.UnsupportedEncodingException;
 
@@ -137,8 +136,8 @@ public class ApiInvoker {
   /*
     Format to {@code Pair} objects.
   */
-  public static Set<Pair> parameterToPairs(String collectionFormat, String name, Object value){
-    Set<Pair> params = new HashSet<Pair>();
+  public static List<Pair> parameterToPairs(String collectionFormat, String name, Object value){
+    List<Pair> params = new ArrayList<Pair>();
 
     // preconditions
     if (name == null || name.isEmpty()) return params;
@@ -247,7 +246,7 @@ public class ApiInvoker {
     }
   }
 
-  public String invokeAPI(String host, String path, String method, Set<Pair> queryParams, Object body, Map<String, String> headerParams, Map<String, String> formParams, String contentType) throws ApiException {
+  public String invokeAPI(String host, String path, String method, List<Pair> queryParams, Object body, Map<String, String> headerParams, Map<String, String> formParams, String contentType) throws ApiException {
     HttpClient client = getClient(host);
 
     StringBuilder b = new StringBuilder();
diff --git a/samples/client/petstore/android-java/src/main/java/io/swagger/client/ApiInvoker.java b/samples/client/petstore/android-java/src/main/java/io/swagger/client/ApiInvoker.java
index f831a54c14bc..c55e127cddff 100644
--- a/samples/client/petstore/android-java/src/main/java/io/swagger/client/ApiInvoker.java
+++ b/samples/client/petstore/android-java/src/main/java/io/swagger/client/ApiInvoker.java
@@ -23,8 +23,7 @@ import java.util.Collection;
 import java.util.Map;
 import java.util.HashMap;
 import java.util.List;
-import java.util.Set;
-import java.util.HashSet;
+import java.util.ArrayList;
 import java.io.IOException;
 import java.io.UnsupportedEncodingException;
 
@@ -137,8 +136,8 @@ public class ApiInvoker {
   /*
     Format to {@code Pair} objects.
   */
-  public static Set<Pair> parameterToPairs(String collectionFormat, String name, Object value){
-    Set<Pair> params = new HashSet<Pair>();
+  public static List<Pair> parameterToPairs(String collectionFormat, String name, Object value){
+    List<Pair> params = new ArrayList<Pair>();
 
     // preconditions
     if (name == null || name.isEmpty()) return params;
@@ -247,7 +246,7 @@ public class ApiInvoker {
     }
   }
 
-  public String invokeAPI(String host, String path, String method, Set<Pair> queryParams, Object body, Map<String, String> headerParams, Map<String, String> formParams, String contentType) throws ApiException {
+  public String invokeAPI(String host, String path, String method, List<Pair> queryParams, Object body, Map<String, String> headerParams, Map<String, String> formParams, String contentType) throws ApiException {
     HttpClient client = getClient(host);
 
     StringBuilder b = new StringBuilder();
diff --git a/samples/client/petstore/android-java/src/main/java/io/swagger/client/api/PetApi.java b/samples/client/petstore/android-java/src/main/java/io/swagger/client/api/PetApi.java
index 8580512c7426..21ee69d089be 100644
--- a/samples/client/petstore/android-java/src/main/java/io/swagger/client/api/PetApi.java
+++ b/samples/client/petstore/android-java/src/main/java/io/swagger/client/api/PetApi.java
@@ -53,7 +53,7 @@ public class PetApi {
     String path = "/pet".replaceAll("\\{format\\}","json");
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     // header params
     Map<String, String> headerParams = new HashMap<String, String>();
     // form params
@@ -107,7 +107,7 @@ public class PetApi {
     String path = "/pet".replaceAll("\\{format\\}","json");
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     // header params
     Map<String, String> headerParams = new HashMap<String, String>();
     // form params
@@ -161,7 +161,7 @@ public class PetApi {
     String path = "/pet/findByStatus".replaceAll("\\{format\\}","json");
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     // header params
     Map<String, String> headerParams = new HashMap<String, String>();
     // form params
@@ -217,7 +217,7 @@ public class PetApi {
     String path = "/pet/findByTags".replaceAll("\\{format\\}","json");
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     // header params
     Map<String, String> headerParams = new HashMap<String, String>();
     // form params
@@ -278,7 +278,7 @@ public class PetApi {
     String path = "/pet/{petId}".replaceAll("\\{format\\}","json").replaceAll("\\{" + "petId" + "\\}", apiInvoker.escapeString(petId.toString()));
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     // header params
     Map<String, String> headerParams = new HashMap<String, String>();
     // form params
@@ -339,7 +339,7 @@ public class PetApi {
     String path = "/pet/{petId}".replaceAll("\\{format\\}","json").replaceAll("\\{" + "petId" + "\\}", apiInvoker.escapeString(petId.toString()));
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     // header params
     Map<String, String> headerParams = new HashMap<String, String>();
     // form params
@@ -409,7 +409,7 @@ public class PetApi {
     String path = "/pet/{petId}".replaceAll("\\{format\\}","json").replaceAll("\\{" + "petId" + "\\}", apiInvoker.escapeString(petId.toString()));
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     // header params
     Map<String, String> headerParams = new HashMap<String, String>();
     // form params
@@ -472,7 +472,7 @@ public class PetApi {
     String path = "/pet/{petId}/uploadImage".replaceAll("\\{format\\}","json").replaceAll("\\{" + "petId" + "\\}", apiInvoker.escapeString(petId.toString()));
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     // header params
     Map<String, String> headerParams = new HashMap<String, String>();
     // form params
diff --git a/samples/client/petstore/android-java/src/main/java/io/swagger/client/api/StoreApi.java b/samples/client/petstore/android-java/src/main/java/io/swagger/client/api/StoreApi.java
index e038962ac6ee..49a3ac4aa9a1 100644
--- a/samples/client/petstore/android-java/src/main/java/io/swagger/client/api/StoreApi.java
+++ b/samples/client/petstore/android-java/src/main/java/io/swagger/client/api/StoreApi.java
@@ -52,7 +52,7 @@ public class StoreApi {
     String path = "/store/inventory".replaceAll("\\{format\\}","json");
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     // header params
     Map<String, String> headerParams = new HashMap<String, String>();
     // form params
@@ -106,7 +106,7 @@ public class StoreApi {
     String path = "/store/order".replaceAll("\\{format\\}","json");
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     // header params
     Map<String, String> headerParams = new HashMap<String, String>();
     // form params
@@ -165,7 +165,7 @@ public class StoreApi {
     String path = "/store/order/{orderId}".replaceAll("\\{format\\}","json").replaceAll("\\{" + "orderId" + "\\}", apiInvoker.escapeString(orderId.toString()));
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     // header params
     Map<String, String> headerParams = new HashMap<String, String>();
     // form params
@@ -224,7 +224,7 @@ public class StoreApi {
     String path = "/store/order/{orderId}".replaceAll("\\{format\\}","json").replaceAll("\\{" + "orderId" + "\\}", apiInvoker.escapeString(orderId.toString()));
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     // header params
     Map<String, String> headerParams = new HashMap<String, String>();
     // form params
diff --git a/samples/client/petstore/android-java/src/main/java/io/swagger/client/api/UserApi.java b/samples/client/petstore/android-java/src/main/java/io/swagger/client/api/UserApi.java
index f8096cb2a87c..a16a745c7f8a 100644
--- a/samples/client/petstore/android-java/src/main/java/io/swagger/client/api/UserApi.java
+++ b/samples/client/petstore/android-java/src/main/java/io/swagger/client/api/UserApi.java
@@ -53,7 +53,7 @@ public class UserApi {
     String path = "/user".replaceAll("\\{format\\}","json");
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     // header params
     Map<String, String> headerParams = new HashMap<String, String>();
     // form params
@@ -107,7 +107,7 @@ public class UserApi {
     String path = "/user/createWithArray".replaceAll("\\{format\\}","json");
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     // header params
     Map<String, String> headerParams = new HashMap<String, String>();
     // form params
@@ -161,7 +161,7 @@ public class UserApi {
     String path = "/user/createWithList".replaceAll("\\{format\\}","json");
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     // header params
     Map<String, String> headerParams = new HashMap<String, String>();
     // form params
@@ -216,7 +216,7 @@ public class UserApi {
     String path = "/user/login".replaceAll("\\{format\\}","json");
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     // header params
     Map<String, String> headerParams = new HashMap<String, String>();
     // form params
@@ -273,7 +273,7 @@ public class UserApi {
     String path = "/user/logout".replaceAll("\\{format\\}","json");
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     // header params
     Map<String, String> headerParams = new HashMap<String, String>();
     // form params
@@ -332,7 +332,7 @@ public class UserApi {
     String path = "/user/{username}".replaceAll("\\{format\\}","json").replaceAll("\\{" + "username" + "\\}", apiInvoker.escapeString(username.toString()));
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     // header params
     Map<String, String> headerParams = new HashMap<String, String>();
     // form params
@@ -392,7 +392,7 @@ public class UserApi {
     String path = "/user/{username}".replaceAll("\\{format\\}","json").replaceAll("\\{" + "username" + "\\}", apiInvoker.escapeString(username.toString()));
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     // header params
     Map<String, String> headerParams = new HashMap<String, String>();
     // form params
@@ -451,7 +451,7 @@ public class UserApi {
     String path = "/user/{username}".replaceAll("\\{format\\}","json").replaceAll("\\{" + "username" + "\\}", apiInvoker.escapeString(username.toString()));
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     // header params
     Map<String, String> headerParams = new HashMap<String, String>();
     // form params
diff --git a/samples/client/petstore/java/src/main/java/io/swagger/client/ApiClient.java b/samples/client/petstore/java/src/main/java/io/swagger/client/ApiClient.java
index b0258026896b..4d50ab3ce849 100644
--- a/samples/client/petstore/java/src/main/java/io/swagger/client/ApiClient.java
+++ b/samples/client/petstore/java/src/main/java/io/swagger/client/ApiClient.java
@@ -22,8 +22,7 @@ import java.util.Map;
 import java.util.Map.Entry;
 import java.util.HashMap;
 import java.util.List;
-import java.util.Set;
-import java.util.HashSet;
+import java.util.ArrayList;
 import java.util.Date;
 import java.util.TimeZone;
 
@@ -242,8 +241,8 @@ public class ApiClient {
   /*
     Format to {@code Pair} objects.
   */
-  public Set<Pair> parameterToPairs(String collectionFormat, String name, Object value){
-    Set<Pair> params = new HashSet<Pair>();
+  public List<Pair> parameterToPairs(String collectionFormat, String name, Object value){
+    List<Pair> params = new ArrayList<Pair>();
 
     // preconditions
     if (name == null || name.isEmpty()) return params;
@@ -403,7 +402,7 @@ public class ApiClient {
    * @param authNames The authentications to apply
    * @return The response body in type of string
    */
-  public String invokeAPI(String path, String method, Set<Pair> queryParams, Object body, Map<String, String> headerParams, Map<String, String> formParams, String accept, String contentType, String[] authNames) throws ApiException {
+  public String invokeAPI(String path, String method, List<Pair> queryParams, Object body, Map<String, String> headerParams, Map<String, String> formParams, String accept, String contentType, String[] authNames) throws ApiException {
     updateParamsForAuth(authNames, queryParams, headerParams);
 
     Client client = getClient();
@@ -521,7 +520,7 @@ public class ApiClient {
    *
    * @param authNames The authentications to apply
    */
-  private void updateParamsForAuth(String[] authNames, Set<Pair> queryParams, Map<String, String> headerParams) {
+  private void updateParamsForAuth(String[] authNames, List<Pair> queryParams, Map<String, String> headerParams) {
     for (String authName : authNames) {
       Authentication auth = authentications.get(authName);
       if (auth == null) throw new RuntimeException("Authentication undefined: " + authName);
diff --git a/samples/client/petstore/java/src/main/java/io/swagger/client/api/PetApi.java b/samples/client/petstore/java/src/main/java/io/swagger/client/api/PetApi.java
index 922084ec48f8..402fc9da953d 100644
--- a/samples/client/petstore/java/src/main/java/io/swagger/client/api/PetApi.java
+++ b/samples/client/petstore/java/src/main/java/io/swagger/client/api/PetApi.java
@@ -55,7 +55,7 @@ public class PetApi {
     String path = "/pet".replaceAll("\\{format\\}","json");
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     Map<String, String> headerParams = new HashMap<String, String>();
     Map<String, String> formParams = new HashMap<String, String>();
 
@@ -112,7 +112,7 @@ public class PetApi {
     String path = "/pet".replaceAll("\\{format\\}","json");
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     Map<String, String> headerParams = new HashMap<String, String>();
     Map<String, String> formParams = new HashMap<String, String>();
 
@@ -169,7 +169,7 @@ public class PetApi {
     String path = "/pet/findByStatus".replaceAll("\\{format\\}","json");
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     Map<String, String> headerParams = new HashMap<String, String>();
     Map<String, String> formParams = new HashMap<String, String>();
 
@@ -228,7 +228,7 @@ public class PetApi {
     String path = "/pet/findByTags".replaceAll("\\{format\\}","json");
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     Map<String, String> headerParams = new HashMap<String, String>();
     Map<String, String> formParams = new HashMap<String, String>();
 
@@ -293,7 +293,7 @@ public class PetApi {
       .replaceAll("\\{" + "petId" + "\\}", apiClient.escapeString(petId.toString()));
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     Map<String, String> headerParams = new HashMap<String, String>();
     Map<String, String> formParams = new HashMap<String, String>();
 
@@ -358,7 +358,7 @@ public class PetApi {
       .replaceAll("\\{" + "petId" + "\\}", apiClient.escapeString(petId.toString()));
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     Map<String, String> headerParams = new HashMap<String, String>();
     Map<String, String> formParams = new HashMap<String, String>();
 
@@ -436,7 +436,7 @@ public class PetApi {
       .replaceAll("\\{" + "petId" + "\\}", apiClient.escapeString(petId.toString()));
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     Map<String, String> headerParams = new HashMap<String, String>();
     Map<String, String> formParams = new HashMap<String, String>();
 
@@ -503,7 +503,7 @@ public class PetApi {
       .replaceAll("\\{" + "petId" + "\\}", apiClient.escapeString(petId.toString()));
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     Map<String, String> headerParams = new HashMap<String, String>();
     Map<String, String> formParams = new HashMap<String, String>();
 
diff --git a/samples/client/petstore/java/src/main/java/io/swagger/client/api/StoreApi.java b/samples/client/petstore/java/src/main/java/io/swagger/client/api/StoreApi.java
index a94a57990c3d..498b6d4a6b89 100644
--- a/samples/client/petstore/java/src/main/java/io/swagger/client/api/StoreApi.java
+++ b/samples/client/petstore/java/src/main/java/io/swagger/client/api/StoreApi.java
@@ -54,7 +54,7 @@ public class StoreApi {
     String path = "/store/inventory".replaceAll("\\{format\\}","json");
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     Map<String, String> headerParams = new HashMap<String, String>();
     Map<String, String> formParams = new HashMap<String, String>();
 
@@ -111,7 +111,7 @@ public class StoreApi {
     String path = "/store/order".replaceAll("\\{format\\}","json");
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     Map<String, String> headerParams = new HashMap<String, String>();
     Map<String, String> formParams = new HashMap<String, String>();
 
@@ -174,7 +174,7 @@ public class StoreApi {
       .replaceAll("\\{" + "orderId" + "\\}", apiClient.escapeString(orderId.toString()));
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     Map<String, String> headerParams = new HashMap<String, String>();
     Map<String, String> formParams = new HashMap<String, String>();
 
@@ -237,7 +237,7 @@ public class StoreApi {
       .replaceAll("\\{" + "orderId" + "\\}", apiClient.escapeString(orderId.toString()));
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     Map<String, String> headerParams = new HashMap<String, String>();
     Map<String, String> formParams = new HashMap<String, String>();
 
diff --git a/samples/client/petstore/java/src/main/java/io/swagger/client/api/UserApi.java b/samples/client/petstore/java/src/main/java/io/swagger/client/api/UserApi.java
index a8e2fa37a85a..3bff204ac02b 100644
--- a/samples/client/petstore/java/src/main/java/io/swagger/client/api/UserApi.java
+++ b/samples/client/petstore/java/src/main/java/io/swagger/client/api/UserApi.java
@@ -55,7 +55,7 @@ public class UserApi {
     String path = "/user".replaceAll("\\{format\\}","json");
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     Map<String, String> headerParams = new HashMap<String, String>();
     Map<String, String> formParams = new HashMap<String, String>();
 
@@ -112,7 +112,7 @@ public class UserApi {
     String path = "/user/createWithArray".replaceAll("\\{format\\}","json");
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     Map<String, String> headerParams = new HashMap<String, String>();
     Map<String, String> formParams = new HashMap<String, String>();
 
@@ -169,7 +169,7 @@ public class UserApi {
     String path = "/user/createWithList".replaceAll("\\{format\\}","json");
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     Map<String, String> headerParams = new HashMap<String, String>();
     Map<String, String> formParams = new HashMap<String, String>();
 
@@ -227,7 +227,7 @@ public class UserApi {
     String path = "/user/login".replaceAll("\\{format\\}","json");
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     Map<String, String> headerParams = new HashMap<String, String>();
     Map<String, String> formParams = new HashMap<String, String>();
 
@@ -287,7 +287,7 @@ public class UserApi {
     String path = "/user/logout".replaceAll("\\{format\\}","json");
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     Map<String, String> headerParams = new HashMap<String, String>();
     Map<String, String> formParams = new HashMap<String, String>();
 
@@ -350,7 +350,7 @@ public class UserApi {
       .replaceAll("\\{" + "username" + "\\}", apiClient.escapeString(username.toString()));
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     Map<String, String> headerParams = new HashMap<String, String>();
     Map<String, String> formParams = new HashMap<String, String>();
 
@@ -414,7 +414,7 @@ public class UserApi {
       .replaceAll("\\{" + "username" + "\\}", apiClient.escapeString(username.toString()));
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     Map<String, String> headerParams = new HashMap<String, String>();
     Map<String, String> formParams = new HashMap<String, String>();
 
@@ -477,7 +477,7 @@ public class UserApi {
       .replaceAll("\\{" + "username" + "\\}", apiClient.escapeString(username.toString()));
 
     // query params
-    Set<Pair> queryParams = new HashSet<Pair>();
+    List<Pair> queryParams = new ArrayList<Pair>();
     Map<String, String> headerParams = new HashMap<String, String>();
     Map<String, String> formParams = new HashMap<String, String>();
 
diff --git a/samples/client/petstore/java/src/main/java/io/swagger/client/auth/ApiKeyAuth.java b/samples/client/petstore/java/src/main/java/io/swagger/client/auth/ApiKeyAuth.java
index edd98a164141..0e5ca9c7c538 100644
--- a/samples/client/petstore/java/src/main/java/io/swagger/client/auth/ApiKeyAuth.java
+++ b/samples/client/petstore/java/src/main/java/io/swagger/client/auth/ApiKeyAuth.java
@@ -3,7 +3,7 @@ package io.swagger.client.auth;
 import io.swagger.client.Pair;
 
 import java.util.Map;
-import java.util.Set;
+import java.util.List;
 
 public class ApiKeyAuth implements Authentication {
   private final String location;
@@ -42,7 +42,7 @@ public class ApiKeyAuth implements Authentication {
   }
 
   @Override
-  public void applyToParams(Set<Pair> queryParams, Map<String, String> headerParams) {
+  public void applyToParams(List<Pair> queryParams, Map<String, String> headerParams) {
     String value;
     if (apiKeyPrefix != null) {
       value = apiKeyPrefix + " " + apiKey;
diff --git a/samples/client/petstore/java/src/main/java/io/swagger/client/auth/Authentication.java b/samples/client/petstore/java/src/main/java/io/swagger/client/auth/Authentication.java
index 32e61103cd7a..98b1a6900b93 100644
--- a/samples/client/petstore/java/src/main/java/io/swagger/client/auth/Authentication.java
+++ b/samples/client/petstore/java/src/main/java/io/swagger/client/auth/Authentication.java
@@ -3,9 +3,9 @@ package io.swagger.client.auth;
 import io.swagger.client.Pair;
 
 import java.util.Map;
-import java.util.Set;
+import java.util.List;
 
 public interface Authentication {
   /** Apply authentication settings to header and query params. */
-  void applyToParams(Set<Pair> queryParams, Map<String, String> headerParams);
+  void applyToParams(List<Pair> queryParams, Map<String, String> headerParams);
 }
diff --git a/samples/client/petstore/java/src/main/java/io/swagger/client/auth/HttpBasicAuth.java b/samples/client/petstore/java/src/main/java/io/swagger/client/auth/HttpBasicAuth.java
index 0f2428222acb..980b24311bea 100644
--- a/samples/client/petstore/java/src/main/java/io/swagger/client/auth/HttpBasicAuth.java
+++ b/samples/client/petstore/java/src/main/java/io/swagger/client/auth/HttpBasicAuth.java
@@ -3,7 +3,7 @@ package io.swagger.client.auth;
 import io.swagger.client.Pair;
 
 import java.util.Map;
-import java.util.Set;
+import java.util.List;
 
 import java.io.UnsupportedEncodingException;
 import javax.xml.bind.DatatypeConverter;
@@ -29,7 +29,7 @@ public class HttpBasicAuth implements Authentication {
   }
 
   @Override
-  public void applyToParams(Set<Pair> queryParams, Map<String, String> headerParams) {
+  public void applyToParams(List<Pair> queryParams, Map<String, String> headerParams) {
     String str = (username == null ? "" : username) + ":" + (password == null ? "" : password);
     try {
       headerParams.put("Authorization", "Basic " + DatatypeConverter.printBase64Binary(str.getBytes("UTF-8")));
diff --git a/samples/client/petstore/java/src/main/java/io/swagger/client/auth/OAuth.java b/samples/client/petstore/java/src/main/java/io/swagger/client/auth/OAuth.java
index e0b8f942b39c..39fba5498c0e 100644
--- a/samples/client/petstore/java/src/main/java/io/swagger/client/auth/OAuth.java
+++ b/samples/client/petstore/java/src/main/java/io/swagger/client/auth/OAuth.java
@@ -3,11 +3,11 @@ package io.swagger.client.auth;
 import io.swagger.client.Pair;
 
 import java.util.Map;
-import java.util.Set;
+import java.util.List;
 
 public class OAuth implements Authentication {
   @Override
-  public void applyToParams(Set<Pair> queryParams, Map<String, String> headerParams) {
+  public void applyToParams(List<Pair> queryParams, Map<String, String> headerParams) {
     // TODO: support oauth
   }
 }
diff --git a/samples/client/petstore/java/src/test/java/io/swagger/client/auth/ApiKeyAuthTest.java b/samples/client/petstore/java/src/test/java/io/swagger/client/auth/ApiKeyAuthTest.java
index 1f0c150cabbe..5bdb4fb78fba 100644
--- a/samples/client/petstore/java/src/test/java/io/swagger/client/auth/ApiKeyAuthTest.java
+++ b/samples/client/petstore/java/src/test/java/io/swagger/client/auth/ApiKeyAuthTest.java
@@ -1,9 +1,9 @@
 package io.swagger.client.auth;
 
 import java.util.HashMap;
-import java.util.HashSet;
+import java.util.ArrayList;
 import java.util.Map;
-import java.util.Set;
+import java.util.List;
 
 import io.swagger.client.Pair;
 import org.junit.*;
@@ -13,7 +13,7 @@ import static org.junit.Assert.*;
 public class ApiKeyAuthTest {
     @Test
     public void testApplyToParamsInQuery() {
-        Set<Pair> queryParams = new HashSet<Pair>();
+        List<Pair> queryParams = new ArrayList<Pair>();
         Map<String, String> headerParams = new HashMap<String, String>();
 
         ApiKeyAuth auth = new ApiKeyAuth("query", "api_key");
@@ -31,7 +31,7 @@ public class ApiKeyAuthTest {
 
     @Test
     public void testApplyToParamsInHeaderWithPrefix() {
-            Set<Pair> queryParams = new HashSet<Pair>();
+            List<Pair> queryParams = new ArrayList<Pair>();
         Map<String, String> headerParams = new HashMap<String, String>();
 
         ApiKeyAuth auth = new ApiKeyAuth("header", "X-API-TOKEN");
diff --git a/samples/client/petstore/java/src/test/java/io/swagger/client/auth/HttpBasicAuthTest.java b/samples/client/petstore/java/src/test/java/io/swagger/client/auth/HttpBasicAuthTest.java
index 562daa5ba897..52c5497ba83e 100644
--- a/samples/client/petstore/java/src/test/java/io/swagger/client/auth/HttpBasicAuthTest.java
+++ b/samples/client/petstore/java/src/test/java/io/swagger/client/auth/HttpBasicAuthTest.java
@@ -1,9 +1,9 @@
 package io.swagger.client.auth;
 
 import java.util.HashMap;
-import java.util.HashSet;
+import java.util.ArrayList;
 import java.util.Map;
-import java.util.Set;
+import java.util.List;
 
 import io.swagger.client.Pair;
 import org.junit.*;
@@ -20,7 +20,7 @@ public class HttpBasicAuthTest {
 
     @Test
     public void testApplyToParams() {
-        Set<Pair> queryParams = new HashSet<Pair>();
+        List<Pair> queryParams = new ArrayList<Pair>();
         Map<String, String> headerParams = new HashMap<String, String>();
 
         auth.setUsername("my-username");