Support CSV Deserialization to EnumMaps

During the last years I did a lot of CSV reading (with and without Jackson). When parsing this type of data with Jackson, I often serialize rows to maps, when there is some sort of dynamics in the data that is impractical to handle with POJO mappers.

This is a typical example:

CsvSchema headerSchema = CsvSchema.emptySchema().withHeader();
MappingIterator<Map<String, String>> it = mapper
                .readerForMapOf(String.class)
                .with(schema)
                .readValues(input);
while (it.hasNext()) {
  Map<String, String> row = it.nextValue();
  String xVal = row.get("x");
  String yVal = row.get("y");
  String temperature = row.get("temperature");
  // do something with the values
  ...
}

The usual situation is that all the valid header values stem from a fixed set of strings, so there is an immediate association with Java Enums. I would like to do something like this:

enum MyEnum {
  X, Y, TEMPERATURE, HUMIDITY, ... ;
}

static MyEnum parse(String s) {
  ... // a separate method or an implementation detail of the enum class
}

...

CsvSchema headerSchema = CsvSchema.emptySchema().withHeader();
MappingIterator<EnumMap<MyEnum, String>> it = mapper
                .readerForMapOf(MyEnum.class, h -> parse(h), String) // specify enum type, mapping function header->enum, value class
                .with(schema)
                .readValues(input);
while (it.hasNext()) {
  EnumMap<MyEnum, String> row = it.nextValue();
  String xVal = row.get(X);
  String yVal = row.get(Y);
  String temperature = row.get(TEMPERATURE);
  // do something with the values
  ...
}

Besides rigour, Enum headers / EnumMaps have other advantages, such as internal optimizations for speed and memory footprint (compared to HashMap or LinkedHashMap).

Would that proposal be something that is within the scope of this library?

[cowtowncoder]

Ok, so what I mean is that would adding of @JsonCreator next to parse method work – it should, I think. And for serialization, @JsonValue next to method code().

In fact, I think that use of @JsonValue should handle both cases, if external representation is the value that method returns.

This aspect of Enums is not well documented as improvements have been added piece by piece over time.

Finally, also notice that you can use @JsonProperty on enum entries: value specified is the external value (one included in JSON) to use, and would override Enum.name().

[cowtowncoder]

At this point, this issue would properly belong in jackson-databind. Could you file it there? I think SKIP_UNKNOWN_MAP_KEYS would make sense (it is slightly redundant as only Maps have keys, but it seems reasonable to me wrt existing feature naming).