java无法将null Jackson节点反序列化到集合

Question

当我的JsonNode没有值时，我正在测试deserializing到collection对象。我希望对象等于null

这就是我要尝试的：

public class ImmutableDiscoveredUrlDeserializer extends JsonDeserializer<ImmutableDiscoveredUrl> {
String parentUrl;
Double parentUrlSentiment;
Set<String> childUrls;
Boolean isParentVendorUrl;
Map<TagClassification, Set<String>> parentUrlArticleTags;

/*
 * (non-Javadoc)
 * @see com.fasterxml.jackson.databind.JsonDeserializer#deserialize(com.fasterxml.jackson.core.JsonParser, com.fasterxml.jackson.databind.DeserializationContext)
 */
@Override
public ImmutableDiscoveredUrl deserialize(JsonParser p, DeserializationContext ctx)
    throws IOException {

    JsonNode node = p.readValueAsTree();
    parentUrl = defaultIfNull(node.get("parentUrl").asText(), null);
    childUrls = defaultIfNull(parseChildUrls(node), emptySet());
    isParentVendorUrl = defaultIfNull(Boolean.valueOf(node.get("isParentVendorUrl").asText()), null);
    parentUrlArticleTags = defaultIfNull(parseArticleTags(node.get("parentUrlArticleTags")), emptyMap());

    return ImmutableDiscoveredUrl.discoveredUrl().parentUrl(parentUrl)
                .parentUrlSentiment(parentUrlSentiment).childUrls(childUrls)
            .isParentVendorUrl(isParentVendorUrl).parentUrlArticleTags(parentUrlArticleTags);
}

private Set<String> parseChildUrls(JsonNode node) throws IOException {
    ObjectMapper tagsMapper = new ObjectMapper();
    return tagsMapper.convertValue(node, new TypeReference<Set<String>>() {});
}

private Map<TagClassification, Set<String>> parseArticleTags(JsonNode node) throws IOException {
    ObjectMapper tagsMapper = new ObjectMapper();
    return tagsMapper.convertValue(node, new TypeReference<Set<String>>() {});
}

但我得到一个MismatchedInputException，声明没有可映射的内容。如何让ObjectMapper返回空值

Answer 1

在我的情况下，我有一个小不同的问题，因为

Cannot deserialize instance of `java.util.HashSet` out of START_OBJECT token
 at [Source: (String)"{"bbc":"firstbckt","ssg":{"751fad0":"751fad0","be0eb99":"be0eb99"}}"

这是我的POJO

import java.io.Serializable;
import java.util.Map;
import java.util.Set;
import java.util.stream.Collectors;
import com.google.common.collect.Maps;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@NoArgsConstructor
@AllArgsConstructor
@SuppressWarnings("serial")
public class BulkUploadRsp implements Serializable {
    private String bbc;
    private Map<String, String> ssgs = Maps.newHashMap();
    //..
    public void setSsgs(Set<String> ssgs) {
        this.ssgs = ssgs.stream().collect(Collectors.toMap(ssg -> ssg, ssg -> ssg));
    }
}

问题是：我有一个以set*开头的util方法。将其重命名为setSsgs(Set<String> ssgs)有助于解决该问题