[BUG][JAVA] enum are generated in UPPER_CASE but this breaks json deserialization

[feliksik]

Description

In the default Java generator, enums specified withCamelCasing (example) in the spec are converted to WITHCAMELCASING in the java code ( example ). This is idiomatic, but breaks json deserialization (jackson 2.9.6).

See https://github.com/feliksik/bug-reports/tree/master/openapi-generator/enum-casing for the exact step to reproduce (run mvn generate-sources) .

Workaround:

The following ObjectMapper will make it work; note that there is also a hack WRITE_DATES_AS_TIMESTAMPS, which relates to another dateTime serialization problem i have had (cannot find the issue now). I do not consider this a proper solution if people have to write this themselves, as it's pretty costly to discover and fix this stuff.

new ObjectMapper()
            .registerModule(new JavaTimeModule())
            .enable(DeserializationFeature.READ_ENUMS_USING_TO_STRING)
            .enable(SerializationFeature.WRITE_ENUMS_USING_TO_STRING)
            .disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS); // this is also painful!

Suggest a fix

Options are:

• generate theInputAsIs (although this conflicts with [REQ] Java: Use MACRO_CASE for generated enums #2867 )
• generate an ObjectMapper along with the DTOs, that respects the assumptions made by the generator (would also save the DateTime issues)

[wing328]

@feliksik thanks for reporting the issue. I prefer your 2nd option. Do you mind filing a PR with the suggested fix so that we can review more easily?

[feliksik]

I could take a look, when I have time... Sure.

[jmini]

Which generator are you using?

If you take the java client with okhttp-gson library, the value is stored as enum member and an adapter is generated to do serialization and de-serialization.

@JsonAdapter(StringEnum.Adapter.class)
public enum StringEnum {
  
  MY_VALUE("myValue"),
  
  SOMEHTING_ELSE("somethingElse");

  private String value;

  StringEnum(String value) {
    this.value = value;
  }

  public String getValue() {
    return value;
  }

  @Override
  public String toString() {
    return String.valueOf(value);
  }

  public static StringEnum fromValue(String value) {
    for (StringEnum b : StringEnum.values()) {
      if (b.value.equals(value)) {
        return b;
      }
    }
    throw new IllegalArgumentException("Unexpected value '" + value + "'");
  }

  public static class Adapter extends TypeAdapter<StringEnum> {
    @Override
    public void write(final JsonWriter jsonWriter, final StringEnum enumeration) throws IOException {
      jsonWriter.value(enumeration.getValue());
    }

    @Override
    public StringEnum read(final JsonReader jsonReader) throws IOException {
      String value = jsonReader.nextString();
      return StringEnum.fromValue(value);
    }
  }
}

[feliksik]

@jmini thanks for the input. I did not get to playing around with the generator yet, but seeing different approaches is the best first step.

I used the plain java generator to trigger the issue (see here).

Maybe that Adapter solution is actually nice. I was thinking whether it may also be used for the Dates-as-timestamps to make the custom ObjectMapper unnecessary -- but I'm not sure that's possible.

[hjstorch]

Hello.
Same issue occurred with google-api-client & jackson too.
Thanks!

[Giulioss]

Hi,
same issue occured using <generatorName>java</generatorName>.
Using Typescript i don't have this issue, i'm using https://github.com/OpenAPITools/openapi-generator/blob/master/docs/generators/typescript-rxjs.md.
The property name is enumPropertyNaming, why there is not a java version of this property?

Thanks