Jackson 反序列化器 - 将空集合更改为空集合 [英] Jackson deserializer - change null collection to empty one

问题描述

我有一个包含集合作为属性的实体:

I have an entity that contains collection as attribute:

public class Entity {

    @JsonProperty(value="homes")
    @JsonDeserialize(as=HashSet.class, contentAs=HomeImpl.class)
    private Collection<Home> homes = new ArrayList<Home>();

}

如果请求包含 null 作为请求属性:

If request contains null as request property:

{
  "homes": null
}

然后家被设置为空.我想要做的是将家设置为空列表.我需要为此编写特殊的反序列化器还是有一个用于集合?我尝试的是这个反序列化器，但它看起来很丑(它不是通用的并且使用实现而不是接口).

then homes is set to null. What I want to do is to set homes to empty list. Do I need to write special deserializer for this or is there one for collections? What I tried is this deserializer but it looks ugly (it's not generic and uses implementation instead of interface).

public class NotNullCollectionDeserializer extends JsonDeserializer<Collection<HomeImpl>> {

  @Override
  public Collection<HomeImpl> deserialize(final JsonParser jsonParser, final DeserializationContext deserializationContext) throws IOException, JsonProcessingException {
    return jsonParser.readValueAs(new TypeReference<Collection<HomeImpl>>(){});
  }

  @Override
  public Collection<HomeImpl> getNullValue() {
    return Collections.emptyList();
  }
}

这么几个问题:

1. 是否有一些 jackson 属性在反序列化期间将 null 更改为空集合?
2. 如果第一点没有 - 我是否需要为此编写反序列化器?如果是，我可以写一个通用的吗?

推荐答案

我也找不到 Jackson 属性或对此的注释.所以我必须对第一个问题回答否".但我会推荐一个简单的 setter 而不是特殊的解串器:

I also couldn't find a Jackson property or annotation for this. So I'll have to answer no to the first question. But I would recommend a simple setter instead of the special deserializer :

public class Entity {

    @JsonDeserialize(contentAs = HomeImpl.class)
    private Collection<Home> homes = new ArrayList<>();

    public void setHomes(List<Home> homes) {
        if (homes != null)
            this.homes = homes;
    }
}

这是通用的，因为它只使用 Home 接口而不是 HomeImpl.您不需要 @JsonProperty，因为 Jackson 会将 setHomes 和 homes 关联起来.

This is generic as it only uses the Home interface instead of HomeImpl. You don't need @JsonProperty as Jackson will associate setHomes and homes.

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