Jackson deserialization error handling

Question

My problem is fairly simple : I have the following simple class:

public class Foo {
   private int id = -1;
   public void setId(int _id){ this.id = _id; }
   public int getId(){ return this.id; }
}

And I am trying to process following JSON:

{
  "id": "blah"
}

Obviously, there is a problem here ("blah" cannot be parsed to an int)

Formerly, Jackson throws something like org.codehaus.jackson.map.JsonMappingException: Can not construct instance of java.lang.Integer from String value 'blah': not a valid Integer value

I agree with this, but I'd like to register something somewhere allowing to ignore this type of mapping errors. I tried with a DeserializationProblemHandler registered (see here) but it seems to only work on unknown properties and not deserialization problems.

Have you any clue on this issue?

Answer 1

I succeeded to solve my problem, thanks to Tatu from Jackson ML.

I had to use custom non blocking deserializers for every primitive types handled in Jackson. Something like this factory :

public class JacksonNonBlockingObjectMapperFactory {

    /**
     * Deserializer that won't block if value parsing doesn't match with target type
     * @param <T> Handled type
     */
    private static class NonBlockingDeserializer<T> extends JsonDeserializer<T> {
        private StdDeserializer<T> delegate;

        public NonBlockingDeserializer(StdDeserializer<T> _delegate){
            this.delegate = _delegate;
        }

        @Override
        public T deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException, JsonProcessingException {
            try {
                return delegate.deserialize(jp, ctxt);
            }catch (JsonMappingException e){
                // If a JSON Mapping occurs, simply returning null instead of blocking things
                return null;
            }
        }
    }

    private List<StdDeserializer> jsonDeserializers = new ArrayList<StdDeserializer>();

    public ObjectMapper createObjectMapper(){
        ObjectMapper objectMapper = new ObjectMapper();

        SimpleModule customJacksonModule = new SimpleModule("customJacksonModule", new Version(1, 0, 0, null));
        for(StdDeserializer jsonDeserializer : jsonDeserializers){
            // Wrapping given deserializers with NonBlockingDeserializer
            customJacksonModule.addDeserializer(jsonDeserializer.getValueClass(), new NonBlockingDeserializer(jsonDeserializer));
        }

        objectMapper.registerModule(customJacksonModule);
        return objectMapper;
    }

    public JacksonNonBlockingObjectMapperFactory setJsonDeserializers(List<StdDeserializer> _jsonDeserializers){
        this.jsonDeserializers = _jsonDeserializers;
        return this;
    }
}

Then calling it like this way (pass as deserializers only those you want to be non blocking) :

JacksonNonBlockingObjectMapperFactory factory = new JacksonNonBlockingObjectMapperFactory();
factory.setJsonDeserializers(Arrays.asList(new StdDeserializer[]{
    // StdDeserializer, here, comes from Jackson (org.codehaus.jackson.map.deser.StdDeserializer)
    new StdDeserializer.ShortDeserializer(Short.class, null),
    new StdDeserializer.IntegerDeserializer(Integer.class, null),
    new StdDeserializer.CharacterDeserializer(Character.class, null),
    new StdDeserializer.LongDeserializer(Long.class, null),
    new StdDeserializer.FloatDeserializer(Float.class, null),
    new StdDeserializer.DoubleDeserializer(Double.class, null),
    new StdDeserializer.NumberDeserializer(),
    new StdDeserializer.BigDecimalDeserializer(),
    new StdDeserializer.BigIntegerDeserializer(),
    new StdDeserializer.CalendarDeserializer()
}));
ObjectMapper om = factory.createObjectMapper();

Answer 2

You might want to let your controller handle the problem by adding a method that handles this specific exception

@ExceptionHandler(HttpMessageNotReadableException.class)
@ResponseBody
public String handleHttpMessageNotReadableException(HttpMessageNotReadableException ex)
{
    JsonMappingException jme = (JsonMappingException) ex.getCause();
    return jme.getPath().get(0).getFieldName() + " invalid";
}

Of course, the line

    JsonMappingException jme = (JsonMappingException) ex.getCause();

might throw a class cast exception for some cases but i haven't encountered them yet.