[BUG][JAVA] Static Initializer Block missing in JSON support class

[bergerchris]

Description

To reproduce the error I just used the Swagger Petstore example. I generated java code with openapi-generator version 7.0.1 and tried to create a model an use toJson() to get the Json-String from the model.

Customer customer = new Customer();
customer.setUsername("test");

String test = customer.toJson();

The result is an NullPointerException: Cannot invoke "com.google.gson.Gson.toJson(Object)" because the return value of "com.domain.test.JSON.getGson()" is null

I think the problem might be, that no static initializer block is used in the JSON support class. There is only an instance initializer block like this

    {
        GsonBuilder gsonBuilder = createGson();
        gsonBuilder.registerTypeAdapter(Date.class, dateTypeAdapter);
        gsonBuilder.registerTypeAdapter(java.sql.Date.class, sqlDateTypeAdapter);
        gsonBuilder.registerTypeAdapter(OffsetDateTime.class, offsetDateTimeTypeAdapter);
        gsonBuilder.registerTypeAdapter(LocalDate.class, localDateTypeAdapter);
        gsonBuilder.registerTypeAdapter(byte[].class, byteArrayAdapter);
        gsonBuilder.registerTypeAdapterFactory(new com.domain.test.model.Address.CustomTypeAdapterFactory());
        gsonBuilder.registerTypeAdapterFactory(new com.domain.test.model.Category.CustomTypeAdapterFactory());
        gsonBuilder.registerTypeAdapterFactory(new com.domain.test.model.Customer.CustomTypeAdapterFactory());
        gsonBuilder.registerTypeAdapterFactory(new com.domain.test.model.ModelApiResponse.CustomTypeAdapterFactory());
        gsonBuilder.registerTypeAdapterFactory(new com.domain.test.model.Order.CustomTypeAdapterFactory());
        gsonBuilder.registerTypeAdapterFactory(new com.domain.test.model.Pet.CustomTypeAdapterFactory());
        gsonBuilder.registerTypeAdapterFactory(new com.domain.test.model.Tag.CustomTypeAdapterFactory());
        gsonBuilder.registerTypeAdapterFactory(new com.domain.test.model.User.CustomTypeAdapterFactory());
        gson = gsonBuilder.create();
    }

When i add "static" to make it a static initializer block everything works as expected.

   static {
        GsonBuilder gsonBuilder = createGson();
        gsonBuilder.registerTypeAdapter(Date.class, dateTypeAdapter);
        gsonBuilder.registerTypeAdapter(java.sql.Date.class, sqlDateTypeAdapter);
        gsonBuilder.registerTypeAdapter(OffsetDateTime.class, offsetDateTimeTypeAdapter);
        gsonBuilder.registerTypeAdapter(LocalDate.class, localDateTypeAdapter);
        gsonBuilder.registerTypeAdapter(byte[].class, byteArrayAdapter);
        gsonBuilder.registerTypeAdapterFactory(new com.domain.test.model.Address.CustomTypeAdapterFactory());
        gsonBuilder.registerTypeAdapterFactory(new com.domain.test.model.Category.CustomTypeAdapterFactory());
        gsonBuilder.registerTypeAdapterFactory(new com.domain.test.model.Customer.CustomTypeAdapterFactory());
        gsonBuilder.registerTypeAdapterFactory(new com.domain.test.model.ModelApiResponse.CustomTypeAdapterFactory());
        gsonBuilder.registerTypeAdapterFactory(new com.domain.test.model.Order.CustomTypeAdapterFactory());
        gsonBuilder.registerTypeAdapterFactory(new com.domain.test.model.Pet.CustomTypeAdapterFactory());
        gsonBuilder.registerTypeAdapterFactory(new com.domain.test.model.Tag.CustomTypeAdapterFactory());
        gsonBuilder.registerTypeAdapterFactory(new com.domain.test.model.User.CustomTypeAdapterFactory());
        gson = gsonBuilder.create();
    }

[JanUlrichR]

Hey, thanks for providing a fix for that issue. Can we estimate when this fix will be merged ?

[wing328]

@JanUlrichR have you tested it locally to confirm the fix?

[wing328]

I've filed #16984 to add a test but it doesn't throw any exception.

How can I properly repeat the issue?

[JanUlrichR]

Hey @wing328 ,
I am a little bit confused about this. In your PR the pipeline shows the exact error that was mentioned in the description.
Applying the changes from blutorange solve that issue.
When checking out the repo and running the test locally i get the same errors as the PR pipeline.
The changes made by blutorange also fixed the problem locally.

[wing328]

When checking out the repo and running the test locally i get the same errors as the PR pipeline.

Are you using sbt to run the test?

I forgot to mention my tests passed locally (and in the CI) when ran with mvn clean package. (I didn't test with sbt locally)

[JanUlrichR]

For me sbt does not work. But the errors I receive seem to be some misconfiguration on my end. (Haven't worked with sbt before)

I checked with maven.

[wing328]

Which version of JDK are you using?

I'm using OpenJDK 11 on Mac