[JAVA] Enum mapping make wrong value as null instead of throwing an exception

[TehBakker]

Description

Short : If I've a value that does not match my enum, the JsonCreator of the enum make it null, where I would want it to throw a validation exception.
This is following #1919 changes

Swagger-codegen version

2.2.3-SNAPSHOT

Swagger declaration file content or url

 MyBean:
      type: object
      required:
        - enumList
      description: Enum list attribute
      properties:
        enumList:
          type: array
          minItems: 1
          items:
            $ref: '#/definitions/MyEnum'

 MyEnum:
      type: string
      description: blabla my enum
      enum:
        - VALUE1
        - VALUE2

The generated code is

public enum MyEnum {
  
  VALUE1("VALUE1"),
  
  VALUE2("VALUE1");

  private String value;

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

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

  @JsonCreator
  public static MyEnum fromValue(String text) {
    for (MyEnum b : MyEnum.values()) {
      if (String.valueOf(b.value).equals(text)) {
        return b;
      }
    }
    return null;
  }
}

Related issues

#1919

Suggest a Fix

What I would like is to be able to say if in case of unknown value, the @JsonCreator should return null like today or throw an exception.
Since my Enum is in a list attribut, I cannot just use @NotNull (and the exception message wouldn't be correct with what is really going on anyway).

Also is there a way to tell a list attribut that it should not contains any null value ?
Such as Jackson READ_UNKNOWN_ENUM_VALUES_AS_NULL property allow to declare ?

Please let me know if I'm not clear enough.

Regards

[wing328]

@TehBakker so basically you want to throw an exception instead of returning null, right? I think it's reasonable and to achieve that without breaking backward-compatibility, the only way seems to be adding another option (e.g. invalidEnumThrowsException)

cc @cbornet

[wing328]

cc @ePaul as well

[TehBakker]

Yes that's exactly that, an extra option would be good yeah.
Although I feel that should have been the default behavior maybe ?

[cbornet]

I think you should be able to configure Jackson READ_UNKNOWN_ENUM_VALUES_AS_NULL from the client without the need to add another option.

[TehBakker]

@cbornet I thought so too, I might have messed up, but I tried setting spring.jackson.deserialization.READ_UNKNOWN_ENUM_VALUES_AS_NULL=false in my application.properties and it didn't seems to have effect.

I think it's because the @JsonCreator generated take precedant over Jackson conf no ?

@JsonCreator
  public static MyEnum fromValue(String text) {
    for (MyEnum b : MyEnum.values()) {
      if (String.valueOf(b.value).equals(text)) {
        return b;
      }
    }
    return null;
  }

[cbornet]

I think the default here should be to throw an exception. Also I'm not sure why we need to use JsonCreator here whereas I think Jackson could handle enum mapping directly using READ_ENUMS_USING_TO_STRING and WRITE_ENUMS_USING_TO_STRING.

[cbornet]

I've checked and it seems all jackson-based java clients set READ_ENUMS_USING_TO_STRING and WRITE_ENUMS_USING_TO_STRING. So I don't understand why we also have @JsonValue/@JsonCreator...
@TehBakker can you check what it gives if you remove the annotations ?

[TehBakker]

Sure, as I said in the original post, it's tied to that ticket #1919
It was added to handle it case insensitively, might make sense sometime but not in all case and returning null is just wrong imo.
If I remove the @JsonCreator it works as expected and throws an InvalidFormatException:

Caused by: com.fasterxml.jackson.databind.exc.InvalidFormatException: Can not deserialize value of type com.mypackage.MyEnum from String "test": value not one of declared Enum instance names: [VALUE1, VALUE2, VALUE2]

[cbornet]

@wing328 do you know if we can remove the annotations and the fromValue() method or is there a good reason not to do it ?

[TehBakker]

Any news on the fix making it into the next release ?

[wing328]

do you know if we can remove the annotations and the fromValue() method or is there a good reason not to do it ?

Seems like it's related to enum marshalling: #4059

@TehBakker what about using the okhttp-gson or retrofit2 Java client instead? You can also use customized templates with the -t option.