java - 从 ObjectMapper 中的 POJO 覆盖 @JsonInclude(Include.NON_NULL)

Question

问题: 是否可以在创建 ObjectMapper 时覆盖 POJO 中定义的 Include.NON_NULL？

解释:

假设我有一个如下所示的 POJO:

@JsonInclude(Include.NON_NULL)
class POJO {
  String name;
  String description;
  //Constructors, Getters & Setters, etc
}

还有一个测试类如下:

class Main {
  public static void main(String args[]) {
    POJO p = new POJO();
    ObjectMapper mapper = new ObjectMapper();
     String jsonString = mapper.setSerializationInclusion(Include.ALWAYS)
                               .writerWithDefaultPrettyPrinter()
                               .writeValueAsString(p);
    //jsonString should contain empty name & description fields, but they doesn't
  }
}

Answer 1

您可以使用混合，因为它优先于注释。

@JsonInclude(JsonInclude.Include.ALWAYS)
public class MixIn {
}

并将其添加到映射器

ObjectMapper mapper = new ObjectMapper();
mapper.addMixIn(POJO.class, MixIn.class);

结果会是

{"name":null,"description":null}