java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to com.testing.models.Account

Question

I'm getting below error:

java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to com.testing.models.Account

with below code

final int expectedId = 1;

Test newTest = create();

int expectedResponseCode = Response.SC_OK;

ArrayList<Account> account = given().when().expect().statusCode(expectedResponseCode)
    .get("accounts/" + newTest.id() + "/users")
    .as(ArrayList.class);
assertThat(account.get(0).getId()).isEqualTo(expectedId);

Is there a reason why I cannot do get(0)?

Cannot be cast to **what**? What is the rest of the error message? — Oliver Charlesworth, Mar 03 '15 at 00:02
What's an `Account`? Why are you trying to cast to it from a map? — Dave Newton, Mar 03 '15 at 00:06
For those of us who might be unfamiliar with the library, can you say what class this `given()` method is statically imported from? — Mark Peters, Mar 03 '15 at 00:07
@DaveNewton `Account` is a model from Dropwizard which uses `com.fasterxml.jackson.databind.annotations` — Passionate Engineer, Mar 03 '15 at 00:08
Seems to me you are trying to deserialize JSON string onto Java object. The problem might be in structure mismatch. You should put here response from this URL:"accounts/" + newClub.getOwner().getCustId() + "/clubs" and Account class — Pavel Niedoba, Mar 03 '15 at 00:12

Mark Peters · Accepted Answer · 2019-03-06T17:05:33.250

150

The issue's coming from Jackson. When it doesn't have enough information on what class to deserialize to, it uses LinkedHashMap.

Since you're not informing Jackson of the element type of your ArrayList, it doesn't know that you want to deserialize into an ArrayList of Accounts. So it falls back to the default.

Instead, you could probably use as(JsonNode.class), and then deal with the ObjectMapper in a richer manner than rest-assured allows. Something like this:

ObjectMapper mapper = new ObjectMapper();

JsonNode accounts = given().when().expect().statusCode(expectedResponseCode)
    .get("accounts/" + newClub.getOwner().getCustId() + "/clubs")
    .as(JsonNode.class);


//Jackson's use of generics here are completely unsafe, but that's another issue
List<Account> accountList = mapper.convertValue(
    accounts, 
    new TypeReference<List<Account>>(){}
);

assertThat(accountList.get(0).getId()).isEqualTo(expectedId);

edited Mar 06 '19 at 17:05

answered Mar 03 '15 at 00:16

Mark Peters

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You can also set the response asString(), saves having to do extra conversions - readValue will accept a String as the first arg. – BIGDeutsch Jun 09 '16 at 09:25
@BIGDeutsch: Just revisiting this, there was no need for me to convert back to tokens there when `convertValue` could do it in one step. Going to a string works too. – Mark Peters Mar 06 '19 at 17:07
what to do when an object contains a varibale which is list . How to deserialize the object using jackson ? – user1887464 Oct 09 '21 at 12:29
very helpful, thanks – danisupr4 Feb 10 '22 at 19:16
Simple and do the work. – mikegrep Dec 31 '22 at 11:22

score 70 · Answer 2 · edited Sep 17 '18 at 16:40

70

Try the following:

POJO pojo = mapper.convertValue(singleObject, POJO.class);

or:

List<POJO> pojos = mapper.convertValue(
    listOfObjects,
    new TypeReference<List<POJO>>() { });

See conversion of LinkedHashMap for more information.

edited Sep 17 '18 at 16:40

ErikE

48,881
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answered Jul 27 '16 at 06:40

user2578871

820
6
5

3

+1 for showing "convertValue". I had a case where I needed to read a particular property out of json as a List and this is exactly what I needed. – GameSalutes Jun 20 '17 at 21:02

score 44 · Answer 3 · answered Sep 15 '17 at 06:52

44

The way I could mitigate the JSON Array to collection of LinkedHashMap objects problem was by using CollectionType rather than a TypeReference . This is what I did and worked:

public <T> List<T> jsonArrayToObjectList(String json, Class<T> tClass) throws IOException {
    ObjectMapper mapper = new ObjectMapper();
    CollectionType listType = mapper.getTypeFactory().constructCollectionType(ArrayList.class, tClass);
    List<T> ts = mapper.readValue(json, listType);
    LOGGER.debug("class name: {}", ts.get(0).getClass().getName());
    return ts;
}

Using the TypeReference, I was still getting an ArrayList of LinkedHashMaps, i.e. does not work:

public <T> List<T> jsonArrayToObjectList(String json, Class<T> tClass) throws IOException {
    ObjectMapper mapper = new ObjectMapper();
    List<T> ts = mapper.readValue(json, new TypeReference<List<T>>(){});
    LOGGER.debug("class name: {}", ts.get(0).getClass().getName());
    return ts;
}

answered Sep 15 '17 at 06:52

Himadri Pant

2,171
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3

Saved my problem as well. Thank you! – Vladimir Gilevich Oct 05 '17 at 14:53
1

+1, the difference in your case was that the method itself was generic so `T` could not be reified via the TypeToken, which is typically easier. Personally I prefer Guava's helper because it's still typesafe and not specific to any container type: `return new TypeToken>(){}.where(new TypeParameter(){}, tClass)`. But Jackson doesn't take `TypeToken`s so you then need `.getType()`. – Mark Peters Nov 24 '17 at 15:22
Saved my problem as well. Thank you! – Shashank Jul 17 '20 at 03:32
Thank you! Spent a lot of time to fix this error untill i found this answer!! – glco Dec 08 '20 at 18:33
Lovely!!. This saved my day as well :)..Struggled for hours before i hit this solution. I was trying to write a genric JSONB array convertor for JOOQ in kotlin. – sumanr Feb 23 '21 at 12:45

nurb · Answer 4 · 2016-07-08T10:02:23.220

6

I had a similar exception (but different problem) - java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to org.bson.Document , and fortunately it's solved easier:

Instead of

List<Document> docs = obj.get("documents");
Document doc = docs.get(0)

which gives error on second line, One can use

List<Document> docs = obj.get("documents");
Document doc = new Document(docs.get(0));

edited Jul 08 '16 at 10:02

answered Jun 06 '16 at 12:02

nurb

325
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How did you set up your constructor for the Document class? – Francislainy Campos Jan 27 '22 at 11:11

score 1 · Answer 5 · answered Nov 05 '20 at 03:47

Solve problem with two method parse common

Whith type is an object

public <T> T jsonToObject(String json, Class<T> type) {
        T target = null;
        try {
            target = objectMapper.readValue(json, type);
        } catch (Jsenter code hereonProcessingException e) {
            e.printStackTrace();
        }
    
        return target;
    }

With type is collection wrap object

public <T> T jsonToObject(String json, TypeReference<T> type) {
    T target = null;
    try {
        target = objectMapper.readValue(json, type);
    } catch (JsonProcessingException e) {
        e.printStackTrace();
    }
    return target;
}

score 1 · Answer 6 · answered May 13 '21 at 05:59

This is something i used in my project, Json object was returned, i converted it to a List of POJO, List and then accessed the element. I took the input of Json object from another microservice.

Main thing is:- JsonNode stocks = restTemplate.getForObject("http://localhost:2000/stocks/qty", JsonNode.class); List<Stock_id_qty> stockList = mapper.convertValue(stocks, new TypeReference<List<Stock_id_qty>>() {});

@GetMapping("/")
    public List<Stock_id_qty> checkQty() throws JsonProcessingException {
        ObjectMapper mapper = new ObjectMapper();
        JsonNode stocks = restTemplate.getForObject("http://localhost:2000/stocks/qty", JsonNode.class);
        List<Stock_id_qty> stockList = mapper.convertValue(stocks, new TypeReference<List<Stock_id_qty>>() {});
        List<Stock_id_qty> result = new ArrayList<>();
        for(Stock_id_qty s : stockList){
            if(s.getStockQty() < 10)
            {
                result.add(s);
            }
        }
        return result;
    }

score 0 · Answer 7 · edited Dec 23 '18 at 18:43

I have this method for deserializing an XML and converting the type:

public <T> Object deserialize(String xml, Class objClass ,TypeReference<T> typeReference ) throws IOException {
    XmlMapper xmlMapper = new XmlMapper();
    Object obj = xmlMapper.readValue(xml,objClass);
    return  xmlMapper.convertValue(obj,typeReference );   
}

and this is the call:

List<POJO> pojos = (List<POJO>) MyUtilClass.deserialize(xml, ArrayList.class,new TypeReference< List< POJO >>(){ });

score 0 · Answer 8 · answered Aug 28 '20 at 10:33

When you use jackson to map from string to your concrete class, especially if you work with generic type. then this issue may happen because of different class loader. i met it one time with below scenarior:

Project B depend on Library A

in Library A:

public class DocSearchResponse<T> {
 private T data;
}

it has service to query data from external source, and use jackson to convert to concrete class

public class ServiceA<T>{
  @Autowired
  private ObjectMapper mapper;
  @Autowired
  private ClientDocSearch searchClient;

  public DocSearchResponse<T> query(Criteria criteria){
      String resultInString = searchClient.search(criteria);
      return convertJson(resultInString)
  }
}

public DocSearchResponse<T> convertJson(String result){
     return mapper.readValue(result, new TypeReference<DocSearchResponse<T>>() {});
  }
}

in Project B:

public class Account{
 private String name;
 //come with other attributes
}

and i use ServiceA from library to make query and as well convert data

public class ServiceAImpl extends ServiceA<Account> {
    
}

and make use of that

public class MakingAccountService {
    @Autowired
    private ServiceA service;
    public void execute(Criteria criteria){
      
        DocSearchResponse<Account> result = service.query(criteria);
        Account acc = result.getData(); //  java.util.LinkedHashMap cannot be cast to com.testing.models.Account
    }
}

it happen because from classloader of LibraryA, jackson can not load Account class, then just override method convertJson in Project B to let jackson do its job

public class ServiceAImpl extends ServiceA<Account> {
        @Override
        public DocSearchResponse<T> convertJson(String result){
         return mapper.readValue(result, new TypeReference<DocSearchResponse<T>>() {});
      }
    }
 }

CodingBee · Answer 9 · 2022-01-28T14:24:54.117

public class ObjectHelper {

  private static ObjectMapper objectMapper = new ObjectMapper();

  public static ObjectMapper getObjectMapper() {
    objectMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL).configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES,false);
    return objectMapper;
  } 
}

Use

FetchResponse fetchResponse =
ObjectHelper.getObjectMapper().convertValue(
                    data, new TypeReference<FetchResponse>() {});

OR

List<Map<String, Object>> responseObj = (List<Map<String, Object>>) response.get("content");

List<LkAuthUserDetail> responseData = ObjectHelper.getObjectMapper().convertValue(responseObj,
                    new TypeReference<List<LkAuthUserDetail>>() {});

java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to com.testing.models.Account

9 Answers9

Linked