Treating "N/A" value as null with Jackson

Question

I am getting data from an external JSON API and parsing the result with Jackson. Unfortunately, that API returns all fields as String and those are filled with "N/A" when data is unavailable.

I would like to replace those fields with null, especially as those are frustrating when I try to convert JSON String fields to more informative Java fields.

A custom DeserializationProblemHandler worked for Integer fields (see below), but it was useless for Java 8's LocalDate fields. Furthermore, it reacts to a problem rather than anticipating it.

I was unable to find a pre-processor to configure into my ObjectMapper and am uneasy with the idea of overriding the BeanDeserializer.

Do you know of a better/cleaner solution to handle this kind of situations? Thanks!

---

DeserializationProblemHandler

new DeserializationProblemHandler() {
    @Override
    public Object handleWeirdStringValue(DeserializationContext ctxt, Class<?> targetType, String valueToConvert, String failureMsg) throws IOException {
        return "N/A".equals(valueToConvert) ? null : super.handleWeirdStringValue(ctxt, targetType, valueToConvert, failureMsg);
    }
}

---

Error message when processing "N/A" in LocalDate field

Can not deserialize value of type java.time.LocalDate from String "N/A": Text 'N/A' could not be parsed at index 0

(works fine when there is date in the data)

Answer 1

I feel like there ought to be a better way of doing this, but the following is the only solution I was able to come up with.

Create a new JsonDeserializer that handles "N/A" input. The following example handles strings:

public class EmptyStringDeserializer extends StdScalarDeserializer<String> {
    public EmptyStringDeserializer() {
        super(String.class);
    }

    @Override
    public String deserialize(JsonParser parser, DeserializationContext ctx) throws IOException {
        final String val = parser.getValueAsString();

        if ("N/A".equalsIgnoreCase(val))
            return null;

        return val;
    }
}

The class is registered with an ObjectMapper like this:

SimpleModule simpleModule = new SimpleModule().addDeserializer(String.class, new EmptyStringDeserializer());
ObjectMapper om = new ObjectMapper().registerModule(simpleModule);

You'll probably want to collect all your converters in a module named for the API that is making you handle things this way.