java - 如果没有自定义序列化程序，是否可以对这个字符串进行 Jackson 序列化？

Question

我想序列化我作为 POJO 收到的 JSON 字符串，以便在我的代码中进一步使用，但我很难在不编写自定义序列化程序的情况下让它工作。

我更喜欢作为不编写自定义序列化程序的解决方案，但如果这是唯一可能的方法，我会编写一个。

此外，我认为我收到的数据是一个奇怪的 JSON，因为我请求的列表不是使用 [] 作为列表发送的，而是作为使用 {} 的对象发送的。

我收到以下列表/对象(缩写):

{
    "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"
        }
    }
}

我像这样为内部对象创建了我的第一个 POJO:

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;
  }
}

这本身就很好。现在我写了另一个 POJO 作为数据的包装器，上面一层看起来像这样:

public class CurrencyListDTO implements Serializable {

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

  public CurrencyListDTO()
  {
  }

}

添加注释 @JsonAnySetter 或使用 @JsonCreator 都没有帮助，所以我再次删除了它们，现在我想知道哪个小技巧可以启用 json 的正确序列化。

我的异常(exception)情况如下:

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"])

Answer 1

您应该将 CurrencyListDTO 更改为:

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

因为响应对象中的results字段是另一个以currencyId为键的对象，没有数组。

然后您可以像这样创建您的货币列表:

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