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)

Jackson doesn't generally concern itself with handling specific values of JSON fields. Text based preprocessing may very well be the simplest and most efficient solution for this: `String filteredJson = jsonString.replace("\"N/A\"", "null");`. Otherwise consider catching/handling the Exception. — Manos Nikolaidis, May 15 '17 at 13:37
I actually thought of it. Just didn't find a way to implement it in my Spring Boot application. All I can do is configure my ObjectMapper. — Chop, May 15 '17 at 21:00

Henrik Aasted Sørensen · Answer 1 · 2017-05-15T13:47:07.553

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.

Yup, thought of it, went this way. What held my hand is that it prevents me from using Jackson default Deserializers. I have to reimplement all of them. I even tried to make a proxy Deserializer (if "N/A", return null; else call a deserializer), but I don't know which Deserializer Jackson uses for some of my fields. — Chop, May 15 '17 at 21:02

Treating "N/A" value as null with Jackson

1 Answers1