diff --git a/modules/openapi-generator/src/main/resources/Java/libraries/okhttp-gson/JSON.mustache b/modules/openapi-generator/src/main/resources/Java/libraries/okhttp-gson/JSON.mustache
index 4ab99a19c9a..c6075a08694 100644
--- a/modules/openapi-generator/src/main/resources/Java/libraries/okhttp-gson/JSON.mustache
+++ b/modules/openapi-generator/src/main/resources/Java/libraries/okhttp-gson/JSON.mustache
@@ -116,7 +116,7 @@ public class JSON {
         return clazz;
     }
 
-    {
+    static {
         GsonBuilder gsonBuilder = createGson();
         gsonBuilder.registerTypeAdapter(Date.class, dateTypeAdapter);
         gsonBuilder.registerTypeAdapter(java.sql.Date.class, sqlDateTypeAdapter);
diff --git a/samples/client/echo_api/java/okhttp-gson/src/main/java/org/openapitools/client/JSON.java b/samples/client/echo_api/java/okhttp-gson/src/main/java/org/openapitools/client/JSON.java
index ad091f5cb54..00da6bda9de 100644
--- a/samples/client/echo_api/java/okhttp-gson/src/main/java/org/openapitools/client/JSON.java
+++ b/samples/client/echo_api/java/okhttp-gson/src/main/java/org/openapitools/client/JSON.java
@@ -93,7 +93,7 @@ public class JSON {
         return clazz;
     }
 
-    {
+    static {
         GsonBuilder gsonBuilder = createGson();
         gsonBuilder.registerTypeAdapter(Date.class, dateTypeAdapter);
         gsonBuilder.registerTypeAdapter(java.sql.Date.class, sqlDateTypeAdapter);
diff --git a/samples/client/others/java/okhttp-gson-oneOf/src/main/java/org/openapitools/client/JSON.java b/samples/client/others/java/okhttp-gson-oneOf/src/main/java/org/openapitools/client/JSON.java
index dfe971b780f..f4e972e414e 100644
--- a/samples/client/others/java/okhttp-gson-oneOf/src/main/java/org/openapitools/client/JSON.java
+++ b/samples/client/others/java/okhttp-gson-oneOf/src/main/java/org/openapitools/client/JSON.java
@@ -93,7 +93,7 @@ public class JSON {
         return clazz;
     }
 
-    {
+    static {
         GsonBuilder gsonBuilder = createGson();
         gsonBuilder.registerTypeAdapter(Date.class, dateTypeAdapter);
         gsonBuilder.registerTypeAdapter(java.sql.Date.class, sqlDateTypeAdapter);
diff --git a/samples/client/others/java/okhttp-gson-streaming/src/main/java/org/openapitools/client/JSON.java b/samples/client/others/java/okhttp-gson-streaming/src/main/java/org/openapitools/client/JSON.java
index dc02eac223b..2aac67fb5b2 100644
--- a/samples/client/others/java/okhttp-gson-streaming/src/main/java/org/openapitools/client/JSON.java
+++ b/samples/client/others/java/okhttp-gson-streaming/src/main/java/org/openapitools/client/JSON.java
@@ -93,7 +93,7 @@ public class JSON {
         return clazz;
     }
 
-    {
+    static {
         GsonBuilder gsonBuilder = createGson();
         gsonBuilder.registerTypeAdapter(Date.class, dateTypeAdapter);
         gsonBuilder.registerTypeAdapter(java.sql.Date.class, sqlDateTypeAdapter);
diff --git a/samples/client/petstore/java/okhttp-gson-3.1/src/main/java/org/openapitools/client/JSON.java b/samples/client/petstore/java/okhttp-gson-3.1/src/main/java/org/openapitools/client/JSON.java
index 72223340f53..1e8826d32e8 100644
--- a/samples/client/petstore/java/okhttp-gson-3.1/src/main/java/org/openapitools/client/JSON.java
+++ b/samples/client/petstore/java/okhttp-gson-3.1/src/main/java/org/openapitools/client/JSON.java
@@ -122,7 +122,7 @@ public class JSON {
         return clazz;
     }
 
-    {
+    static {
         GsonBuilder gsonBuilder = createGson();
         gsonBuilder.registerTypeAdapter(Date.class, dateTypeAdapter);
         gsonBuilder.registerTypeAdapter(java.sql.Date.class, sqlDateTypeAdapter);
diff --git a/samples/client/petstore/java/okhttp-gson-awsv4signature/src/main/java/org/openapitools/client/JSON.java b/samples/client/petstore/java/okhttp-gson-awsv4signature/src/main/java/org/openapitools/client/JSON.java
index 87cf7eba101..ad2d26cbfbb 100644
--- a/samples/client/petstore/java/okhttp-gson-awsv4signature/src/main/java/org/openapitools/client/JSON.java
+++ b/samples/client/petstore/java/okhttp-gson-awsv4signature/src/main/java/org/openapitools/client/JSON.java
@@ -93,7 +93,7 @@ public class JSON {
         return clazz;
     }
 
-    {
+    static {
         GsonBuilder gsonBuilder = createGson();
         gsonBuilder.registerTypeAdapter(Date.class, dateTypeAdapter);
         gsonBuilder.registerTypeAdapter(java.sql.Date.class, sqlDateTypeAdapter);
diff --git a/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/JSON.java b/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/JSON.java
index d30a32b2d78..349f4ff8113 100644
--- a/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/JSON.java
+++ b/samples/client/petstore/java/okhttp-gson-dynamicOperations/src/main/java/org/openapitools/client/JSON.java
@@ -133,7 +133,7 @@ public class JSON {
         return clazz;
     }
 
-    {
+    static {
         GsonBuilder gsonBuilder = createGson();
         gsonBuilder.registerTypeAdapter(Date.class, dateTypeAdapter);
         gsonBuilder.registerTypeAdapter(java.sql.Date.class, sqlDateTypeAdapter);
diff --git a/samples/client/petstore/java/okhttp-gson-group-parameter/src/main/java/org/openapitools/client/JSON.java b/samples/client/petstore/java/okhttp-gson-group-parameter/src/main/java/org/openapitools/client/JSON.java
index 87cf7eba101..ad2d26cbfbb 100644
--- a/samples/client/petstore/java/okhttp-gson-group-parameter/src/main/java/org/openapitools/client/JSON.java
+++ b/samples/client/petstore/java/okhttp-gson-group-parameter/src/main/java/org/openapitools/client/JSON.java
@@ -93,7 +93,7 @@ public class JSON {
         return clazz;
     }
 
-    {
+    static {
         GsonBuilder gsonBuilder = createGson();
         gsonBuilder.registerTypeAdapter(Date.class, dateTypeAdapter);
         gsonBuilder.registerTypeAdapter(java.sql.Date.class, sqlDateTypeAdapter);
diff --git a/samples/client/petstore/java/okhttp-gson-nullable-required/src/main/java/org/openapitools/client/JSON.java b/samples/client/petstore/java/okhttp-gson-nullable-required/src/main/java/org/openapitools/client/JSON.java
index d377df7d282..75faa7a82b3 100644
--- a/samples/client/petstore/java/okhttp-gson-nullable-required/src/main/java/org/openapitools/client/JSON.java
+++ b/samples/client/petstore/java/okhttp-gson-nullable-required/src/main/java/org/openapitools/client/JSON.java
@@ -93,7 +93,7 @@ public class JSON {
         return clazz;
     }
 
-    {
+    static {
         GsonBuilder gsonBuilder = createGson();
         gsonBuilder.registerTypeAdapter(Date.class, dateTypeAdapter);
         gsonBuilder.registerTypeAdapter(java.sql.Date.class, sqlDateTypeAdapter);
diff --git a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/JSON.java b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/JSON.java
index d30a32b2d78..349f4ff8113 100644
--- a/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/JSON.java
+++ b/samples/client/petstore/java/okhttp-gson-parcelableModel/src/main/java/org/openapitools/client/JSON.java
@@ -133,7 +133,7 @@ public class JSON {
         return clazz;
     }
 
-    {
+    static {
         GsonBuilder gsonBuilder = createGson();
         gsonBuilder.registerTypeAdapter(Date.class, dateTypeAdapter);
         gsonBuilder.registerTypeAdapter(java.sql.Date.class, sqlDateTypeAdapter);
diff --git a/samples/client/petstore/java/okhttp-gson-swagger1/src/main/java/org/openapitools/client/JSON.java b/samples/client/petstore/java/okhttp-gson-swagger1/src/main/java/org/openapitools/client/JSON.java
index 87cf7eba101..ad2d26cbfbb 100644
--- a/samples/client/petstore/java/okhttp-gson-swagger1/src/main/java/org/openapitools/client/JSON.java
+++ b/samples/client/petstore/java/okhttp-gson-swagger1/src/main/java/org/openapitools/client/JSON.java
@@ -93,7 +93,7 @@ public class JSON {
         return clazz;
     }
 
-    {
+    static {
         GsonBuilder gsonBuilder = createGson();
         gsonBuilder.registerTypeAdapter(Date.class, dateTypeAdapter);
         gsonBuilder.registerTypeAdapter(java.sql.Date.class, sqlDateTypeAdapter);
diff --git a/samples/client/petstore/java/okhttp-gson-swagger2/src/main/java/org/openapitools/client/JSON.java b/samples/client/petstore/java/okhttp-gson-swagger2/src/main/java/org/openapitools/client/JSON.java
index 87cf7eba101..ad2d26cbfbb 100644
--- a/samples/client/petstore/java/okhttp-gson-swagger2/src/main/java/org/openapitools/client/JSON.java
+++ b/samples/client/petstore/java/okhttp-gson-swagger2/src/main/java/org/openapitools/client/JSON.java
@@ -93,7 +93,7 @@ public class JSON {
         return clazz;
     }
 
-    {
+    static {
         GsonBuilder gsonBuilder = createGson();
         gsonBuilder.registerTypeAdapter(Date.class, dateTypeAdapter);
         gsonBuilder.registerTypeAdapter(java.sql.Date.class, sqlDateTypeAdapter);
diff --git a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/JSON.java b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/JSON.java
index 10113fefcc8..f47d2be80f5 100644
--- a/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/JSON.java
+++ b/samples/client/petstore/java/okhttp-gson/src/main/java/org/openapitools/client/JSON.java
@@ -229,7 +229,7 @@ public class JSON {
         return clazz;
     }
 
-    {
+    static {
         GsonBuilder gsonBuilder = createGson();
         gsonBuilder.registerTypeAdapter(Date.class, dateTypeAdapter);
         gsonBuilder.registerTypeAdapter(java.sql.Date.class, sqlDateTypeAdapter);