lpinto.eu lpinto.eu - 1 year ago 212
Java Question

Jersey: Can not deserialize instance of ArrayList out of String

I have a json based REST Web Service implemented using:
Jetty, Jersey, Jersey-JSON using Jackson.

One of my methods receives a Person instance, which has a field of type List<String>.

Public class Person {
List<String> names;

If I call it with an array of names, all works ok! e.g.:

{ "names" : [ "Jhon", "Doe" ] }

But if the person has only one name, my client creates a single value element, e.g.:

{ "names" : "Jhon" }

When I try to call the service with a single value, I get an exception:

Can not deserialize instance of java.util.ArrayList out of VALUE_STRING token


How should I create/configure my web service, in order to be able to deserialize array field when they are sent to me as a single element.


I already read:

Jackson deserialization - with contained ArrayList<T>


How can I customize serialization of a list of JAXB objects to JSON?

and this that refer the last answer:

Jersey client can not deserializable json services - exception(can not deserialize instance)

Jaxb json missing brackets for one element array

But none of those fix the problem.

Thank you in advance!

Answer Source

After a long day, and another... after reading lots of wikis and faqs, it finally works.

What I did:

  1. Use Jackson
  2. Force Jackson providers usage
  3. Define custom deserializer
  4. activate the ACCEPT_SINGLE_VALUE_AS_ARRAY flag
  5. Fix dependencies

The story:

I was using Jersey 1.13 that uses (I belive) jaxb by default.

I changed it to use Jackson


as described at:


This made my jersey use jackson, but the problem remains; jackson can't deserializer the array yet.

I forced the usage of Jackson providers:



Was a needed step, but not enough. It's necessary to activate the ACCEPT_SINGLE_VALUE_AS_ARRAY flag.

ObjectMapper objectMapper;
objectMapper = new ObjectMapper().configure(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY, true);

I needed define custom deserializer

public class MyResolver implements ContextResolver<ObjectMapper> {

    public ObjectMapper getContext(final Class<?> objectType) {
        return objectMapper;

in order to do that:


After doing all of this it still didn't work...

After some more search time, I found:

Jackson 2.0 with Jersey 1.12

That discusses dependencies problems..

This reveled my problem, Jersey v1.13 ships with Jackson v1.9.2 I need Jackson v2.0

I removed dependency for jersey-json, because it included jackson 1.9.2:


And directly declared dependency for:




Note: this change removes the Jersey ability to use Jaxb or jettison.

Off topic, may be interesting for someone:

Configure Jersey/Jackson to NOT use @XmlElement field annotation for JSON field naming

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