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

The problem is the JSON - this cannot, by default, be deserialized into a Collection because it's not actually a JSON Array - that would look like this:

[
    {
        "name": "Test order1",
        "detail": "ahk ks"
    },
    {
        "name": "Test order2",
        "detail": "Fisteku"
    }
]

Since you're not controlling the exact process of deserialization (RestEasy does) - a first option would be to simply inject the JSON as a String and then take control of the deserialization process:

Collection<COrder> readValues = new ObjectMapper().readValue(
    jsonAsString, new TypeReference<Collection<COrder>>() { }
);

You would loose a bit of the convenience of not having to do that yourself, but you would easily sort out the problem.

Another option - if you cannot change the JSON - would be to construct a wrapper to fit the structure of your JSON input - and use that instead of Collection<COrder>.

Hope this helps.

Instead of the JSON document, you can update the ObjectMapper object like below :

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