如何从JSON反序列化到LocalDate，同时还使用JsonGenerator.Feature.WRITE_NUMBERS_AS_STRINGS？

Question

I have enabled jackson-datatype-joda , but it's not working with the JsonGenerator.Feature.WRITE_NUMBERS_AS_STRINGS .

I have set up ObjectMapper as following:

ObjectMapper jacksonObjectMapper = new ObjectMapper();
jacksonObjectMapper.configure(JsonGenerator.Feature.WRITE_NUMBERS_AS_STRINGS, true);
jacksonObjectMapper.registerModule(new JodaModule());

When deserializing (using com.fasterxml.jackson.datatype.joda.deser.LocalDateDeserializer ), I end up with the error:

org.springframework.http.converter.HttpMessageNotReadableException: Could not read JSON: Current token (VALUE_STRING) not numeric, can not use numeric value accessors
at [...]; nested exception is com.fasterxml.jackson.databind.JsonMappingException: Current token (VALUE_STRING) not numeric, can not use numeric value accessors

I've debugged the LocalDateDeserializer and found out, that it's expecting VALUE_NUMBER_INT - while the JsonGenerator.Feature.WRITE_NUMBERS_AS_STRINGS makes the date having Strings.

When I've turned off that Feature, everything was all right.

Is there any possibility that this feature (or similar) will work with Joda Time?

Answer 1

Joda module uses com.fasterxml.jackson.datatype.joda.deser.LocalDateDeserializer for deserializing org.joda.time.LocalDate objects. This class looks like this:

@Override
public LocalDate deserialize(JsonParser jp, DeserializationContext ctxt)
    throws IOException, JsonProcessingException
{
    // [yyyy,mm,dd]
    if (jp.isExpectedStartArrayToken()) {
        jp.nextToken(); // VALUE_NUMBER_INT 
        int year = jp.getIntValue(); 
        jp.nextToken(); // VALUE_NUMBER_INT
        int month = jp.getIntValue();
        jp.nextToken(); // VALUE_NUMBER_INT
        int day = jp.getIntValue();
        if (jp.nextToken() != JsonToken.END_ARRAY) {
            throw ctxt.wrongTokenException(jp, JsonToken.END_ARRAY, "after LocalDate ints");
        }
        return new LocalDate(year, month, day);
    }
    switch (jp.getCurrentToken()) {
    case VALUE_NUMBER_INT:
        return new LocalDate(jp.getLongValue());            
    case VALUE_STRING:
        String str = jp.getText().trim();
        if (str.length() == 0) { // [JACKSON-360]
            return null;
        }
        return parser.parseLocalDate(str);
    default:
    }
    throw ctxt.wrongTokenException(jp, JsonToken.START_ARRAY, "expected JSON Array, String or Number");
}

As you can see, if LocalDate is array this deserializer expects ints in this array. You can write your custom deserializer and extend this implementation. See below example:

class LocalDateWithStringsDeserializer extends LocalDateDeserializer {

    private static final long serialVersionUID = 1L;

    @Override
    public LocalDate deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException,
            JsonProcessingException {
        // [yyyy,mm,dd] or ["yyyy","mm","dd"]
        if (jp.isExpectedStartArrayToken()) {
            return parseArray(jp, ctxt);
        }

        return super.deserialize(jp, ctxt);
    }

    private LocalDate parseArray(JsonParser jp, DeserializationContext ctxt)
            throws JsonParseException, IOException {
        int year = getNextValue(jp);
        int month = getNextValue(jp);
        int day = getNextValue(jp);
        if (jp.nextToken() != JsonToken.END_ARRAY) {
            throw ctxt.wrongTokenException(jp, JsonToken.END_ARRAY, "after LocalDate ints");
        }
        return new LocalDate(year, month, day);
    }

    private int getNextValue(JsonParser jp) throws IOException, JsonParseException {
        jp.nextToken();

        return new Integer(jp.getText());
    }
}

Now you can link above deserializer and your property:

@JsonDeserialize(using = LocalDateWithStringsDeserializer.class)
private LocalDate date;