Java Jackson：JSON值未知

Question

我仍在学习如何使用Jackson。

所以我有一个JSON对象，该对象的值有时是Integer，长String或List

值：整数

{
  "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：清单

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

所以总的来说...

{
  {
      "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"],
      ...
  }
}

这是我的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;
  ... ...

这是我的映射器代码

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

问题是当我执行代码时，出现以下错误：

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

对我来说，这很明显是因为“值”可以包含三种不同类型之一，如何使我的代码足够灵活以容纳这些类型...我总是可以在其他方法中检测值是否为int，List或String，但我首先需要建模（不是）...

我的问题很简单：如何使我的代码足够灵活以适应类型...

Answer 1

如果可以是Integer ， List和String则可以将其声明为Object ，并稍后使用instanceof将其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，可以编写类似于以下内容的逻辑：

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语句适合您的问题，但是它是json对象中的所有字符串格式，因此您必须找出一种从值识别数据类型的方法。 例如，将Integer.valueOf(value)标识为int; 以[开头为身份列表； 另一个是字符串类型。 您可以参考此答案 ，这是将json字符串转换为对象或列表的一般方法。