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 lt Account gt  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

User · Answer

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  lt T gt  List lt T gt  jsonArrayToObjectList String json  Class lt T gt  tClass  throws IOException       ObjectMapper mapper   new ObjectMapper        CollectionType listType   mapper getTypeFactory   constructCollectionType ArrayList class  tClass       List lt T gt  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  lt T gt  List lt T gt  jsonArrayToObjectList String json  Class lt T gt  tClass  throws IOException       ObjectMapper mapper   new ObjectMapper        List lt T gt  ts   mapper readValue json  new TypeReference lt List lt T gt  gt            LOGGER debug  class name       ts get 0  getClass   getName         return ts

User · Answer

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 lt Account gt  accountList   mapper convertValue      accounts       new TypeReference lt List lt Account gt  gt          assertThat accountList get 0  getId    isEqualTo expectedId

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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 lt T gt     private T data     it has service to query data from external source  and use jackson to convert to concrete class public class ServiceA lt T gt      Autowired   private ObjectMapper mapper     Autowired   private ClientDocSearch searchClient     public DocSearchResponse lt T gt  query Criteria criteria         String resultInString   searchClient search criteria         return convertJson resultInString         public DocSearchResponse lt T gt  convertJson String result        return mapper readValue result  new TypeReference lt DocSearchResponse lt T gt  gt                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 lt Account gt            and make use of that public class MakingAccountService        Autowired     private ServiceA service      public void execute Criteria criteria                  DocSearchResponse lt Account gt  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 lt Account gt             Override         public DocSearchResponse lt T gt  convertJson String result            return mapper readValue result  new TypeReference lt DocSearchResponse lt T gt  gt

User · Answer

Solve problem with two method parse common  Whith type is an object  public  lt T gt  T jsonToObject String json  Class lt T gt  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  lt T gt  T jsonToObject String json  TypeReference lt T gt  type        T target   null      try           target   objectMapper readValue json  type         catch  JsonProcessingException e            e printStackTrace              return target

User · Answer

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 lt Document gt  docs   obj get  documents    Document doc   docs get 0    which gives error on second line  One can use      List lt Document gt  docs   obj get  documents    Document doc   new Document docs get 0

User · Answer

I have this method for deserializing an XML and converting the type   public  lt T gt  Object deserialize String xml  Class objClass  TypeReference lt T gt  typeReference   throws IOException       XmlMapper xmlMapper   new XmlMapper        Object obj   xmlMapper readValue xml objClass       return  xmlMapper convertValue obj typeReference           and this is the call   List lt POJO gt  pojos    List lt POJO gt   MyUtilClass deserialize xml  ArrayList class new TypeReference lt  List lt  POJO  gt  gt

User · Answer

Try the following   POJO pojo   mapper convertValue singleObject  POJO class     or   List lt POJO gt  pojos   mapper convertValue      listOfObjects      new TypeReference lt List lt POJO gt  gt            See conversion of LinkedHashMap for more information

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

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