Java Jackson：JSON值未知

Question

我仍在學習如何使用Jackson。

所以我有一個JSON對象，該對象的值有時是Integer，長String或List

值：整數

{
  "id":1,
  "active":1,
  "name":"name1",
  "value":155,
  ...

值：字符串

{
  "id":2,
  "active":1,
  "name":"name2",
  "value":"Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book...",
  ...

值：清單

{
  "id":3,
  "active":1,
  "name":"name3",
  "value":[
    "One",
    "Two",
    "Three",
    "Four"],
  ...

所以總的來說...

{
  {
      "id":1,
      "active":1,
      "name":"name1",
      "value":155,
      ...
  },
  {
      "id":2,
      "active":1,
      "name":"name2",
      "value":"Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book...",
      ...
  },
  {
      "id":3,
      "active":1,
      "name":"name3",
      "value":[
        "One",
        "Two",
        "Three",
        "Four"],
      ...
  }
}

這是我的POJO模型

@JsonIgnoreProperties(ignoreUnknown=true)
@JsonAutoDetect(fieldVisibility= JsonAutoDetect.Visibility.ANY)
public class OQScoresRows {
  private int id;
  private int active;
  private String name;
  private List<String> value;
  ... ...

這是我的映射器代碼

ObjectMapper mapper = new ObjectMapper();
try{
  POJO obj = mapper.readValue(<JSONOBJECT>, POJO.class);
}catch(JsonParseException e){
  return mapper.writeValueAsString(e);
}

問題是當我執行代碼時，出現以下錯誤：

com.fasterxml.jackson.databind.JsonMappingException: Can not deserialize instance of java.util.ArrayList out of VALUE_NUMBER_INT token

對我來說，這很明顯是因為“值”可以包含三種不同類型之一，如何使我的代碼足夠靈活以容納這些類型...我總是可以在其他方法中檢測值是否為int，List或String，但我首先需要建模（不是）...

我的問題很簡單：如何使我的代碼足夠靈活以適應類型...

Answer 1

如果可以是Integer ， List和String則可以將其聲明為Object ，並稍后使用instanceof將其instanceof ，例如：

@JsonIgnoreProperties(ignoreUnknown=true)
@JsonAutoDetect(fieldVisibility= JsonAutoDetect.Visibility.ANY)
public class OQScoresRows {
  private int id;
  private int active;
  private String name;
  private Object value;

反序列化之后，可以編寫類似於以下內容的邏輯：

if(value instanceof Integer){
    //do something after casting it to Integer
}else if(value instanceof List){
    //do something after casting it to List
}else if(value instanceof String){
    do something after casting it to String
}

Answer 2

If-else語句適合您的問題，但是它是json對象中的所有字符串格式，因此您必須找出一種從值識別數據類型的方法。 例如，將Integer.valueOf(value)標識為int; 以[開頭為身份列表； 另一個是字符串類型。 您可以參考此答案 ，這是將json字符串轉換為對象或列表的一般方法。