Handling "Unrecognized token" exception in custom json with Jackson

Question

I'm trying to use the Jackson json parser(v2.5.2) to parse a custom json document that isn't true json and I can't figure out how to make it work. I have a json document that might look like:

{
    "test": {
        "one":"oneThing",
        "two": nonStandardThing(),
        "three": true
    }
}

I want to use the ObjectMapper to map this to a java.util.Map and I would just like the nonStandardThing() to be added as a String value in my map for the key two.

When I run this through the ObjectMapper.readValue(json, Map.class) I get the exception:

com.fasterxml.jackson.core.JsonParseException: Unrecognized token 'nonStandardThing': was expecting 'null', 'true', 'false' or NaN
 at [Source: { "test":{"test1":nonStandardThing(),"test2":"two"}}; line: 1, column: 35]
    at com.fasterxml.jackson.core.JsonParser._constructError(JsonParser.java:1487)
    at com.fasterxml.jackson.core.base.ParserMinimalBase._reportError(ParserMinimalBase.java:518)
    at com.fasterxml.jackson.core.json.ReaderBasedJsonParser._reportInvalidToken(ReaderBasedJsonParser.java:2300)
    at com.fasterxml.jackson.core.json.ReaderBasedJsonParser._reportInvalidToken(ReaderBasedJsonParser.java:2277)

I have tried to register a DeserializationProblemHandler with the ObjectMapper but it is never called when this problem occurs.

Here is sample application that shows what I have tried:

import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.deser.DeserializationProblemHandler;
import java.io.IOException;
import java.util.Map;
import java.util.logging.Level;
import java.util.logging.Logger;

public class JacksonDeserializerTest {
    private Logger log = Logger.getLogger(JacksonDeserializerTest.class.getName());
    public JacksonDeserializerTest() {
        String validJson = "{ \"test\":{\"test1\":\"one\",\"test2\":\"two\"}}";
        String invalidJson = "{ \"test\":{\"test1\":nonStandardThing(),\"test2\":\"two\"}}";

        ObjectMapper mapper = new ObjectMapper();
        mapper.addHandler(new DeserializationProblemHandler() {
            @Override
            public boolean handleUnknownProperty(DeserializationContext dc, JsonParser jp, JsonDeserializer<?> jd, Object bean, String property) throws IOException, JsonProcessingException {
                System.out.println("Handling unknown property: " + property);
                return false;
            }
        });

        try {
            log.log(Level.INFO, "Valid json looks like: {0}", mapper.readValue( validJson, Map.class).toString());
            log.log(Level.INFO, "Invalid json looks like: {0}", mapper.readValue(invalidJson, Map.class).toString());
        } catch (IOException ex) {
            log.log(Level.SEVERE, "Error parsing json", ex);
        }

    }

    public static void main(String[] args) {
        JacksonDeserializerTest test = new JacksonDeserializerTest();
    }
}

The output looks like:

Apr 24, 2015 1:40:27 PM net.acesinc.data.json.generator.jackson.JacksonDeserializerTest <init>
INFO: Valid json looks like: {test={test1=one, test2=two}}
Apr 24, 2015 1:40:27 PM net.acesinc.data.json.generator.jackson.JacksonDeserializerTest <init>
SEVERE: Error parsing json
com.fasterxml.jackson.core.JsonParseException: Unrecognized token 'nonStandardThing': was expecting 'null', 'true', 'false' or NaN
 at [Source: { "test":{"test1":nonStandardThing(),"test2":"two"}}; line: 1, column: 35]
    at com.fasterxml.jackson.core.JsonParser._constructError(JsonParser.java:1487)
    at com.fasterxml.jackson.core.base.ParserMinimalBase._reportError(ParserMinimalBase.java:518)
    at com.fasterxml.jackson.core.json.ReaderBasedJsonParser._reportInvalidToken(ReaderBasedJsonParser.java:2300)
    at com.fasterxml.jackson.core.json.ReaderBasedJsonParser._reportInvalidToken(ReaderBasedJsonParser.java:2277)
    at com.fasterxml.jackson.core.json.ReaderBasedJsonParser._matchToken(ReaderBasedJsonParser.java:2129)

Can anyone point out why the Handler never gets called? Or, if there is a better parse this custom json document (jackson or not...), let me know.

Answer 1

The handler is not called because the invalid part is not the property ("two") but the value (nonStandardThing()).

An obvious way to handle this, is to pass nonStandardThing() as a String, i.e. rewrite the JSON document as

{
    "test": {
        "one":"oneThing",
        "two": "nonStandardThing()",
        "three": true
    }
}

If that is not a possibility, there is not much to do. Using a custom Jackson Deserializer is only useful for properties, not values.

Answer 2

Content you list is unfortunately not valid JSON, so what you have is not really a JSON document, but perhaps serialization of a Javascript object. All String values MUST be enclosed in double quotes in JSON.

Jackson does not support reading of such content directly, but it may be possible to read this using YAML parser like SnakeYAML. Jackson also has YAML data format module at https://github.com/FasterXML/jackson-dataformat-yaml/ so you could perhaps use that. Given that YAML is (mostly!) a superset of JSON, it could probably do what you want.