Allow disabling Integer to String coercion via `CoercionConfig`

[emilkostadinov]

Describe the bug

I am experiencing issues with the new coercion settings that were released in v2.12.0. I would like to disable coercion between String and Integer.

Version information

v2.12.1

To Reproduce

I have class Example (using Lombok annotations):

@Getter
@Setter
@AllArgsConstructor
@NoArgsConstructor
public class Example {
    private String type;
}

The ObjectMapper setup:

ObjectMapper mapper = new ObjectMapper();
mapper.coercionConfigFor(LogicalType.Textual)
        .setCoercion(CoercionInputShape.Integer, CoercionAction.Fail);

How I try to deserialize:

Example example = mapper.readValue("{\"type\": 123}", Example.class);

Expected behavior

I expect an exception to be thrown saying that Integer cannot be converted to String. But what happens is that example is successfully created with type set to "123" which means there was conversion.

Is there anything wrong I do (maybe with the coercion configuration)?

[cowtowncoder]

@e1-emilkostadinov Thank you for reporting this! Your usage of the feature looks correct so that is not the problem.

Up until now coercions from other scalar types to String have been automatically allowed but with the new coercion-config settings it should be possible to prevent this. This requires some work for StringDeserializer (and perhaps couple of other related deserializers) to add applicable checks.

So this is just a case of missing checks and should be implemented: I mark it for 2.13 as the work would most likely be down when starting to consider features to add in 2.13, but it could probably be backported in 2.12 as well if change seems safe enough.

[stephenvsp]

Is there an ETA for 2.13?

[cowtowncoder]

@stephenvsp Not really; I would not expect it before maybe June-July 2021, ideally it'd be relatively small increase but it will have to compete with 3.0 development work.
I haven't had time to look into this feature (and probably won't any time soon), but I can help others with PRs more easily.

[jiamo]

After it success created.
We can only use (Integer) ((Object) map.get("type")) to use the map.

[WojciechLuczkow]

I use following walk-around for 2.12:

Create custom deserializer

public class CoercionLessStringDeserializer extends StringDeserializer {

  @Override
  public String deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {

    List<JsonToken> forbiddenTypes =
        Arrays.asList(
            JsonToken.VALUE_NUMBER_INT,
            JsonToken.VALUE_NUMBER_FLOAT,
            JsonToken.VALUE_TRUE,
            JsonToken.VALUE_FALSE);

    if (forbiddenTypes.contains(p.getCurrentToken())) {
      String message =
          MessageFormat.format("Cannot coerce {0} to String value", p.getCurrentToken());
      throw MismatchedInputException.from(p, String.class, message);
    }
    return super.deserialize(p, ctxt);
  }
}

And use it with objectMapper

      SimpleModule deserializerModule = new SimpleModule();
      deserializerModule.addDeserializer(
          String.class, new CoercionLessStringDeserializer());
      mapper.registerModule(deserializerModule);

More advanced approach would be to use ctxt.findCoercionAction(logicalType(), handledType(), CoercionInputShape.?) for each possible JsonToken.

[cowtowncoder]

Thank you @WojciechLuczkow for showing so anyone who needs a work-around now can use it.
(there are alternatives, such as specifically looking for just VALUE_STRING but above works).