Is Jackson Serialization of this string possible without custom serializer?

Nico :

I want to serialize a JSON-String I receive as a POJO, for further usage in my code, but I am struggling to get it working without writing a custom serializer.

I would prefer as solution without writing a custom serializer, but if that is the only possible way I will write one.

Additionally I believe the data I receive is a weird JSON since the list I request is not sent as list using [] but rather as a object using {}.

I receive the following list/object (shortened):

{
    "results": {
        "ALL": {
            "currencyName": "Albanian Lek",
            "currencySymbol": "Lek",
            "id": "ALL"
        },
        "XCD": {
            "currencyName": "East Caribbean Dollar",
            "currencySymbol": "$",
            "id": "XCD"
        },
        "EUR": {
            "currencyName": "Euro",
            "currencySymbol": "â?¬",
            "id": "EUR"
        },
        "BBD": {
            "currencyName": "Barbadian Dollar",
            "currencySymbol": "$",
            "id": "BBD"
        },
        "BTN": {
            "currencyName": "Bhutanese Ngultrum",
            "id": "BTN"
        },
        "BND": {
            "currencyName": "Brunei Dollar",
            "currencySymbol": "$",
            "id": "BND"
        }
    }
}

I created my first POJO for the inner object like this:

public class CurrencyDTO implements Serializable {

  private String currencyName;
  private String currencySymbol;
  private String currencyId;


  @JsonCreator
  public CurrencyDTO( @JsonProperty( "currencyName" ) String currencyName, @JsonProperty( "currencySymbol" ) String currencySymbol,
                      @JsonProperty( "id" ) String currencyId )
  {
    this.currencyId = currencyId;
    this.currencyName = currencyName;
    this.currencySymbol = currencySymbol;
  }
}

which itself is fine. Now I wrote another POJO as a wrapper for the data a layer above which looks like this:

public class CurrencyListDTO implements Serializable {

  private List<Map<String, CurrencyDTO>> results;

  public CurrencyListDTO()
  {
  }

}

Adding the annotations @JsonAnySetter or using the @JsonCreator didn't help either, so I removed them again and now I am wondering which little trick could enable the correct serialization of the json.

My Exception is the following:

com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize instance of `java.util.ArrayList` out of START_OBJECT token
 at [Source: (String)"{"results":{"ALL":{"currencyName":"Albanian Lek","currencySymbol":"Lek","id":"ALL"},"XCD":{"currencyName":"East Caribbean Dollar","currencySymbol":"$","id":"XCD"},"EUR":{"currencyName":"Euro","currencySymbol":"â?¬","id":"EUR"},"BBD":{"currencyName":"Barbadian Dollar","currencySymbol":"$","id":"BBD"},"BTN":{"currencyName":"Bhutanese Ngultrum","id":"BTN"},"BND":{"currencyName":"Brunei Dollar","currencySymbol":"$","id":"BND"},"XAF":{"currencyName":"Central African CFA Franc","id":"XAF"},"CUP":{"cur"[truncated 10515 chars]; line: 1, column: 12] (through reference chain: com.nico.Banking.api.data.dto.CurrencyListDTO["results"])

Samuel Philipp :

You should change your CurrencyListDTO to:

public class CurrencyListDTO {
    private Map<String, CurrencyDTO> results;
    // getters and setters
}

Because the results field in the response object is another object with the currencyId as key and no array.

You then can create your list of currencies like this:

ObjectMapper mapper = new ObjectMapper();
CurrencyListDTO result = mapper.readValue(json, CurrencyListDTO.class);
List<CurrencyDTO> currencies = new ArrayList<>(result.getResults().values());