java - jackson 没有序列化属性(property)

Question

我有以下两个枚举

public enum Action {
    ACTION1,
    ACTION2,
    ACTION3;
}

public enum EntityType {
    ENTITYTYPE1,
    ENTITYTYPE2;
}

以及下面的类

public class EntityIdentityDto implements MetaData {
    private String id;
    private EntityType entityType;
    private Action action;
    private Map<String, Object> properties = new HashMap();

    public String getId() {
        return this.id;
    }

    public EntityType getEntityType() {
        return this.entityType;
    }

    public Action getAction() {
        return this.action;
    }

    public Map<String, Object> getProperties() {
        return this.properties;
    }

    public void setId(String id) {
        this.id = id;
    }

    public void setEntityType(EntityType entityType) {
          this.entityType = entityType;
    }

    public void setAction(Action action) {
        this.action = action;
    }

    public void setProperties(Map<String, Object> properties) {
        this.properties = properties;
    }

    public EntityIdentityDto() {
    }

}

当使用 Jackson 2.9.8 序列化为 Json 时，如下所示

public class TestMe {
    public static void main(String[] args) throws JsonProcessingException {
        ObjectMapper objectMapper = new ObjectMapper();
        EntityIdentityDto entityIdentityDto = new EntityIdentityDto();
        entityIdentityDto.setEntityType(EntityType.ENTITYTYPE1);
        entityIdentityDto.setAction(Action.ACTION1);
        entityIdentityDto.setId("OOO");
        String out = objectMapper.writeValueAsString(entityIdentityDto);
        System.out.println(out);
    }
}

输出为

{"id":"OOO","action":"ACTION1","properties":{}}

我希望实体类型字段也能序列化，但缺少该字段。这就是我期望看到的

{"id":"OOO","entityType": "ENTITYTYPE1", "action":"ACTION1","properties":{}}

如果我使用 Gson 代替 Jackson，如下所示

public class TestMe {
    public static void main(String[] args) throws JsonProcessingException {
        ObjectMapper objectMapper = new ObjectMapper();
        EntityIdentityDto entityIdentityDto = new EntityIdentityDto();
        entityIdentityDto.setEntityType(EntityType.SYSTEM);
        entityIdentityDto.setAction(Action.SYNC);
        entityIdentityDto.setId("OOO");
        System.out.println(new Gson().toJson(entityIdentityDto));
    }
}

输出符合预期

{"id":"OOO","entityType":"ENTITYTYPE1","action":"ACTION1","properties":{}}

为什么使用 Jackson 生成的 Json 中缺少entityType 字段？有趣的是，action 被序列化，但entityType 却没有序列化，尽管它们在结构上相同并且在 EntityIdentityDto 中使用相同。

Answer 1

可能您没有 entityType 属性的 getter。添加 setter/getter 或使用 setVisibility方法:

ObjectMapper objectMapper = new ObjectMapper();
objectMapper.setVisibility(PropertyAccessor.FIELD, JsonAutoDetect.Visibility.ANY);

另请参阅:

1. how to specify jackson to only use fields - preferably globally
2. Jackson – Decide What Fields Get Serialized/Deserialized
3. Exclude Fields from Serialization in Gson