Java ClassCastException on getting JSON parsed java object

Question

Hi guys I have problem in Java. The problem is around parsing JSON with Jackson as I was instructed. My JSON is parsed well, that's not the problem. The problem lies in that I have multiple JSON items in one JSON. I've parsed it like this:

ObjectMapper objectMapper = new ObjectMapper();

try {
    List<Unit> unitList = objectMapper.readValue(json,List.class);

    System.out.println("UnitSize " + String.valueOf(unitList.size()));
    System.out.println(unitList.get(0).getUnitEmail());
} catch (IOException e) {
    e.printStackTrace();
}

and at UnitSize it'll tell me that I have precisely 5 objects of Unit type, which is okay, but when I want to get something out of the List it says me this:

Exception in thread "main" java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to com.reddatura.API.HTTPRequest$Unit

I've googled it, but nothing relevant. What should be the problem

EDIT:

here is my class snippet:

@JsonIgnoreProperties(ignoreUnknown = true)
public class Unit
{

    @JsonProperty("unitid")
    int unitId;

    @JsonProperty("unitname")
    String unitName;

    @JsonProperty("unitlogo")
    String unitLogo;

    @JsonProperty("unitaddress")
    String unitAddr;
    //other fields, getters setters
    @JsonCreator
    public Unit()
    {

    }
}

I want to parse into this model

You might need to provide some more code. Where exactly are you casting ? — ehanoc
– ehanoc, Commented Oct 22, 2014 at 8:12
You can't cast a Unit to a list. You will have to iterate the list and get the objects one by one — Pedro Oliveira
– Pedro Oliveira, Commented Oct 22, 2014 at 8:13
Try to see what contain unitList.get(0) in the Debug environment. See if it contains Unit or LinkedHashMap — Allan Mermod
– Allan Mermod, Commented Oct 22, 2014 at 8:18

zozelfelfo · Accepted Answer · 2014-10-22 08:15:56Z

1

I think you are not casting correctly your json value:

Using jackson you could do the following:

List<Unit> myUnits = objectMapper.readValue(json, objectMapper.getTypeFactory().
            constructCollectionType(List.class, Unit.class));

Hope it helps :)

answered Oct 22, 2014 at 8:15

zozelfelfo

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8 Comments

Citrus Over a year ago

I don't want to sound rude, but it does not work like this. Gives me error: Unrecognized field "unitid" (Class com.reddatura.API.HTTPRequest), not marked as ignorable when I want to parse it like this :/

zozelfelfo Over a year ago

print your json (or at least part of it) and see if the json is arriving correctly

Citrus Over a year ago

I'm already printing my JSON and it is valid (ran thru a validator also)

zozelfelfo Over a year ago

and the fied unitid is getting value in every jsonobject?

Citrus Over a year ago

yep, it is still there, hence it is a must field

|

Matus · Accepted Answer · 2014-10-23 16:15:25Z

1

try this

 ObjectMapper objectMapper = new ObjectMapper();

        try {
            Unit[] unit = objectMapper.readValue(jsonString, Unit[].class);
            Log.i("TEST", String.valueOf(unit.length)+" ******* "+unit[1].getUnitEmail()+" ******* "+unit[1].getUnitName());

            // or 
            List<Unit> unit1 = objectMapper.readValue(jsonString, new TypeReference<List<Unit>>() { });
            Log.i("TEST_1", String.valueOf(unit1.size())+" ****11111*** "+unit1.get(1).getUnitEmail()+" **1111111**** "+unit1.get(1).getUnitName());

        } catch (IOException e) {
            e.printStackTrace();
    }

answered Oct 23, 2014 at 16:15

Matus

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Comments

Adnan Abdollah Zaki · Accepted Answer · 2015-03-09 07:25:06Z

0

do something like this :

JSONObject jObject = new JSONObject(jsonString);
            JSONArray jsonArray = jObject.getJSONArray("posts");
            for (int i = 0; i < jsonArray.length(); i++) {
                    int a = jsonArray.getJSONObject(i).getInt("a"),
                    String s =  jsonArray.getJSONObject(i).getString("b"));
            }

jsonString is String variable and must be Json syntax

edited Mar 9, 2015 at 7:25

user4644091

answered Oct 22, 2014 at 8:15

Adnan Abdollah Zaki

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