java - Jackson 反序列化子类型将枚举字段设置为 null

Question

更新:删除多余的代码

我需要反序列化一个 JSON 对象，该对象可以是父类的许多子类型之一。具体是哪种子类型由对象中的特定枚举字段决定。我已向父类添加了 @JsonTypeInfo 和 @JsonSubTypes 注释，据我所知，它们都是正确的。

但是，枚举值与 Java 类中的枚举名称并不完全相同。因此，在枚举类中，我使用 @JsonCreator 注解了一个静态方法，以便 Jackson 知道如何将值反序列化为正确的 Java 枚举。

我遇到的问题是，一旦反序列化 JSON 字符串，保存枚举的字段不包含实际的枚举值 - 它保留为 null。

为什么 day 字段保留为 null 以及如何在反序列化过程中按预期设置它？

代码如下。

父日历类

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.EXISTING_PROPERTY, property = "day")
// For the sake of correct deserialisation, we need to map from values of type to child model classes explicitly
@JsonSubTypes({ @JsonSubTypes.Type(value = Monday.class, name = "monday"),
   @JsonSubTypes.Type(value = Monday.class, name = "mon"),
   @JsonSubTypes.Type(value = Tuesday.class, name = "tuesday"),
   @JsonSubTypes.Type(value = Tuesday.class, name = "tues")})
public class Calendar {
   protected String calendarName;
   protected DaysOfWeek day;

   @JsonProperty("calendarName")
   public String getCalendarName() {
      return calendarName;
   }

   public void setCalendarName(String calendarName) {
      this.calendarName = calendarName;
   }

   @JsonProperty("day")
   public DaysOfWeek getDay() {
      return day;
   }

   public void setDay(DaysOfWeek day) {
      this.day = day;
   }
}

周一和周二 child 类(class) 星期一

public class Monday extends Calendar {
   private NegativeFeelings object;

   public Monday() {
   }

   public Monday(NegativeFeelings object) {
      this.object = object;
   }

   @JsonProperty("object")
   public NegativeFeelings getObject() {
      return object;
   }

   public void setObject(NegativeFeelings object) {
      this.object = object;
   }
}

周二

public class Tuesday extends Calendar {
   private Meetings object;

   public Tuesday() {
   }

   public Tuesday(Meetings object) {
      this.object = object;
   }

   @JsonProperty("object")
   public Meetings getObject() {
      return object;
   }

   public void setObject(Meetings object) {
      this.object = object;
   }
}

DaysOfWeek 枚举类

public enum DaysOfWeek {
   MONDAY("monday"),
   MON("mon"),
   TUESDAY("tuesday"),
   TUES("tues");

   private String value;

   DaysOfWeek(String value) {
      this.value = value;
   }

   @Override
   @JsonValue
   public String toString() {
      return String.valueOf(value);
   }

   @JsonCreator
   public static DaysOfWeek fromEventString(@JsonProperty("value") String eventString) {
      return Arrays.stream(DaysOfWeek.values()).filter(e -> e.value.equals(eventString)).findFirst().get();
   }
}

JSON 源字符串

{
  "calendarName":"My Tuesdays",
  "day":"tuesday",
  "object":{
    "meetings":[
      "team",
      "company",
      "client"]
  }
}

反序列化对象(从上面的字符串反序列化)

Tuesday {
  object=Meetings {
  meetings=[team, company, client]
},
  calendarName=My Tuesdays,
  day=null //I want this to be "tuesday", not null
}

Answer 1

通过同事找到了答案。

我需要将 @JsonTypeInfo 注释的 visible 属性设置为 true:

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.EXISTING_PROPERTY, property = "day", visible = true)
// For the sake of correct deserialisation, we need to map from values of type to child model classes explicitly
@JsonSubTypes({ @JsonSubTypes.Type(value = Monday.class, name = "monday"),
   @JsonSubTypes.Type(value = Monday.class, name = "mon"),
   @JsonSubTypes.Type(value = Tuesday.class, name = "tuesday"),
   @JsonSubTypes.Type(value = Tuesday.class, name = "tues")})
public class Calendar {
...