JsonNullable并未与Jackson连载其价值 [英] JsonNullable is not serializing its value with Jackson

问题描述

我正在尝试使用JsonNullable<String>来区分缺少值和null.当我序列化Java对象User时，JsonNullable<String>字段被序列化为带有值的JSON对象

I'm trying to use JsonNullable<String> to distinguish between the absence of a value and null. When I serialize my Java object, User, the JsonNullable<String> field is serialized as a JSON object with value

{"present":false}

由于我使用undefined初始化了该字段，因此我希望它能打印{}.

I'm expecting it to print {} since I initialized the field with undefined.

这是我的课程

public class User { 
  @JsonProperty("userId")
  private JsonNullable<String> userId = JsonNullable.undefined();

  //set and get
  //tostring
}

和一个小的驱动程序，我实际上在JsonNullable字段中设置了一个值.

and a small driver program where I actually set a value within the JsonNullable field.

User user = new User();
user.setUserId(JsonNullable.of("12345"));

ObjectMapper objectMapper = new ObjectMapper();
objectMapper.registerModule(new Jdk8Module());

String expectedData = objectMapper.writeValueAsString(user);
System.out.println(expectedData);

此打印

{"userId":{"present":true}}

但是我期望

{"userId":"12345"}

换句话说，我希望包装在JsonNullable中的值可以序列化到JSON中.为什么JsonNullable和Jackson表现出这种方式?

In other words, I expected the value wrapped within the JsonNullable to be serialized into the JSON. Why are JsonNullable and Jackson behaving this way?

推荐答案

作为

As the wiki instructs, you need to register the corresponding module (in addition to any others you have):

ObjectMapper objectMapper = new ObjectMapper();
objectMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
objectMapper.registerModule(new JsonNullableModule());

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