Question

I have a Json file that looks like this:

[
    { "field":"val" },
....
]

I have Java object representing single object and collection of them:

public class Objects{

    public Collection<List> myObject;
}

I would like to deserialize JSON using ObjectMapper.

ObjectMapper mapper = new ObjectMapper();
mapper.readValue(in, Objects.class);

But I get:

11-24 23:19:19.828: W/UpdateService(6084): org.codehaus.jackson.map.JsonMappingException: 
Can not deserialize instance of com.project.my.Objects out of START_ARRAY token

Answer 1

Try

   mapper.readValue(in, ObjectClass[].class);

Where ObjectClass is something like:

  public class ObjectClass {
    String field;

    public ObjectClass() { }

    public void setField(String value) {
      this.field = value;
    }
  }

Note: in your posted version of the Objects class, you’re declaring a Collection of Lists (i.e. a list of lists), which is not what you want. You probably wanted a List<ObjectClass>. However, it’s much simpler to just do YourObject[].class when deserializing with Jackson, and then converting into a list afterwards.