Question

I want to deserialize some boolean values that I get in a JSON. The problem is that those values can be null, true, false, “true”, false, “Y” or “N”.

I’ve created my own boolean deserializer

public class CustomBooleanDeserializer extends JsonDeserializer<Boolean> {

    final protected Class<?> _valueClass = Boolean.class;

    @Override
    public Boolean deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException,
            JsonProcessingException {
        return _parseBooleanPrimitive2(jp, ctxt);
    }

    protected final boolean _parseBooleanPrimitive2(JsonParser jp, DeserializationContext ctxt)
            throws IOException, JsonProcessingException {
        LogUtils.d("PARSE BOOLEAN");
        JsonToken t = jp.getCurrentToken();
        if (t == JsonToken.VALUE_TRUE) {
            return true;
        }
        if (t == JsonToken.VALUE_FALSE) {
            return false;
        }
        if (t == JsonToken.VALUE_NULL) {
            return false;
        }
        if (t == JsonToken.VALUE_NUMBER_INT) {
            return (jp.getIntValue() != 0);
        }
        if (t == JsonToken.VALUE_STRING) {
            String text = jp.getText().trim();
            if ("true".equals(text)) {
                return true;
            }
            if ("false".equals(text) || text.length() == 0) {
                return Boolean.FALSE;
            }

            if ("N".equalsIgnoreCase(text) || text.length() == 0) {
                return Boolean.FALSE;
            }

            if ("Y".equalsIgnoreCase(text)) {
                return Boolean.TRUE;
            }
            throw ctxt.weirdStringException(_valueClass, "only \"true\" or \"false\" recognized");
        }
        // Otherwise, no can do:
        throw ctxt.mappingException(_valueClass);
    }

However, this deserializer is never called if I register it as this:

Version version = new Version(1, 0, 0, "SNAPSHOT");
SimpleModule module = new SimpleModule("MyModuleName", version);
module = module.addDeserializer(new CustomBooleanDeserializer());
objectMapper.registerModule(module);

If, on the other hand, I use @JsonDeserialize(using = CustomBooleanDeserializer.class) for the boolean fields, it does get called and works great. The only problem is that if the property is null, I get this exception:

org.codehaus.jackson.map.JsonMappingException: Problem deserializing
property ‘show_query_cond’ (expected type: [simple type, class
boolean]; actual type: [NULL]), problem: invalid value for field
(through reference chain: com.csf.model.CSTable[“show_query_cond”])

So, if the boolean property is null, my deserializer doesn’t get a chance to run. Also, I tried using mapper.configure(DeserializationConfig.Feature.FAIL_ON_NULL_FOR_PRIMITIVES, false); but the exception is still thrown if I use the @JsonDeserialize annotation.

Does anyone know how to make this work?

Answer 1

As to registration, this is probably due to Java having both primitive boolean and Object wrapper Boolean. So you need to registed it using both java.lang.Boolean and Boolean.TYPE — latter is the placeholder class for primitive type.

Null handling is different issue: deserialization method is not called for them. However, there is method

JsonDeserializer.getNullValue()

that should be called; and for primitives you must then just return ‘Boolean.FALSE’, since you can not assign null to a primitive value (it is ok to return wrapped; it gets properly handled).