Unable Parse a JSON using Jackson

I have a mongo database call in my code. The response from the database is mapped using codehaus jackson.

Json:

[
  {
    "_id": "555",
    "rates": 1,
    "reviews": [
      {
        "author_name": "Instructor 9999",
        "_authKey": "demo\\556",
        "text": "asdfa",
        "date": 551,
        "_id": "5454-4920",
        "title": "asdf",
        "comments": []
      }
    ],
    "votedUsers": [
      {
        "mng\\39999": 4
      }
    ],
    "rating": 4
  },
  {
    "_id": "45589",
    "rates": 1,
    "reviews": [
      {
        "author_name": "feef",
        "_authKey": "ad\\ads",
        "text": "Working perfect",
        "date": 1498659163,
        "_id": "asdas-319",
        "title": "test",
        "comments": []
      }
    ],
    "votedUsers": [
      {
        "abc\\bis@cdf.com": 4
      }
    ],
    "rating": 4
  }
]

I have created the below DTO Stucture:

@JsonIgnoreProperties(ignoreUnknown = true)
public class MaterialReviewsDTO implements Serializable {

    private static final long serialVersionUID = 1L;
    private String _id;
    private int rates;
    private List<ReviewsDTO> reviews;
    private List<VotedUsersDTO> votedUsers;
    //List<TypeReference<HashMap<String, String>>> votedUsers;
    private int rating;.
    //Getter Setter
}

@JsonIgnoreProperties(ignoreUnknown = true)
public class VotedUsersDTO implements Serializable {

    private static final long serialVersionUID = 1L;
    private Map<String, String> votedUser;
    //Getter Setter
}

Below is the code where I am firing the query:

List<MaterialReviewsDTO> materialReviewsDTOs = DBConnectionRealmByDBName
                    .find(query,
                            MaterialReviewsDTO.class,
                            CollectionNameConstant.REVIEWS_COLLECTION);

Problem is all the JSON is getting mapped in DTO except the below part:

"votedUsers" : [ 
            {
                "abc\\bis@cdf.com" : 4
            }
        ]

VotedUserDTO is null in response. VotedUsers is a list of object containg data in key-value pair.

I am not mentioning ReviewsDTO as this is getting mapped perfectly. How can I map votedUsers part? Note: I am using Spring for development.

Some of the observations from your JSON
1. Json should be designed with Fixed key and variable values in mind.
2. Since in above case both Key and values are variable, we can use Map
So final solution is
change from private List<VotedUsersDTO> votedUsers; to private List<Map<String, Integer>> votedUsers