[英]JAX-RS/Jackson — Deserialize JSON with Unknown Root Element Name?
我正在編寫一個RESTeasy代理客戶端來使用Apple的API來檢索他們的iTunes類別列表。 查詢有關給定類別的信息時,例如使用以下URL:
https://itunes.apple.com/WebObjects/MZStoreServices.woa/ws/genres?id=1420
...你得到一個如下所示的JSON響應:
{
"1420":{
"name":"Self-Help",
"id":"1420",
"url":"https://itunes.apple.com/us/genre/podcasts-health-self-help/id1420?mt=2",
"rssUrls":{
"topVideoPodcastEpisodes":"https://itunes.apple.com/us/rss/topvideopodcastepisodes/genre=1420/json",
"topAudioPodcasts":"https://itunes.apple.com/us/rss/topaudiopodcasts/genre=1420/json",
"topVideoPodcasts":"https://itunes.apple.com/us/rss/topvideopodcasts/genre=1420/json",
"topPodcasts":"https://itunes.apple.com/us/rss/toppodcasts/genre=1420/json",
"topAudioPodcastEpisodes":"https://itunes.apple.com/us/rss/topaudiopodcastepisodes/genre=1420/json",
"topPodcastEpisodes":"https://itunes.apple.com/us/rss/toppodcastepisodes/genre=1420/json"
},
"chartUrls":{
"videoPodcastEpisodes":"https://itunes.apple.com/WebObjects/MZStoreServices.woa/ws/charts?cc=us&g=1420&name=VideoPodcastEpisodes",
"podcasts":"https://itunes.apple.com/WebObjects/MZStoreServices.woa/ws/charts?cc=us&g=1420&name=Podcasts",
"audioPodcastEpisodes":"https://itunes.apple.com/WebObjects/MZStoreServices.woa/ws/charts?cc=us&g=1420&name=AudioPodcastEpisodes",
"audioPodcasts":"https://itunes.apple.com/WebObjects/MZStoreServices.woa/ws/charts?cc=us&g=1420&name=AudioPodcasts",
"podcastEpisodes":"https://itunes.apple.com/WebObjects/MZStoreServices.woa/ws/charts?cc=us&g=1420&name=PodcastEpisodes",
"videoPodcasts":"https://itunes.apple.com/WebObjects/MZStoreServices.woa/ws/charts?cc=us&g=1420&name=VideoPodcasts"
}
}
}
我正在嘗試使用JAXB和Jackson將此JSON響應映射到Java對象。 但是,“1420”根元素名稱似乎導致了問題,因為我在調用客戶端時遇到以下異常:
Unrecognized field "1420" (class foo.bar.ITunesCategoryList), not marked as ignorable
我的JAXB類看起來像這樣:
@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class ITunesCategory implements TransferObject {
private static final long serialVersionUID = 3443545925023804457L;
@XmlElement(name = "id")
@JsonProperty("id")
private String identifier = null;
@XmlElement
private String name = null;
@XmlElementWrapper(name = "subgenres")
private List<ITunesCategory> subcategories = new ArrayList<ITunesCategory>();
...
}
我甚至嘗試創建一個包裝類,因為搜索可能會導致返回多個類別。 它看起來像這樣:
@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class ITunesCategoryList implements TransferObject {
private static final long serialVersionUID = 3303125979016445238L;
@XmlElement
private List<ITunesCategory> categories = new ArrayList<ITunesCategory>();
...
}
但是,無論我指定哪個類作為我的返回類型,我都會得到相同的錯誤,因為類別標識符是JSON對象的根元素名稱。
有沒有辦法告訴JAXB / Jackson / JAX-RS / RESTeasy忽略根元素名稱,只是將底層對象映射到Java? 我無法在開發/編譯時知道根元素名稱,因為它直接對應於搜索返回的結果。 有什么辦法可以解決這個異常嗎? 謝謝你提供的所有幫助!
我無法找到動態忽略根目錄,至少沒有任何適合JAX-RS環境的東西。 我唯一能想到的就是編寫一個自定義反序列化器,然后跳過根節點。 就像是
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import java.io.IOException;
import java.util.Map;
public abstract class IHateRootElemsJsonDeserializer<T> extends JsonDeserializer<T> {
private final ObjectMapper mapper = new ObjectMapper();
private final Class<T> cls;
public IHateRootElemsJsonDeserializer(Class<T> cls) {
this.cls = cls;
}
@Override
public T deserialize(JsonParser jp, DeserializationContext dc)
throws IOException, JsonProcessingException {
JsonNode rootNode = jp.getCodec().readTree(jp);
Map.Entry<String,JsonNode> field = rootNode.fields().next();
JsonNode node = field.getValue();
T result = mapper.convertValue(node, cls);
return result;
}
}
然后用具體類型擴展它。
public class GenreDeserializer extends IHateRootElemsJsonDeserializer<Genre>{
public GenreDeserializer() {
super(Genre.class);
}
}
這是使用您在上面提供的確切JSON的測試
public class Test {
public static void main(String[] args) throws Exception {
ObjectMapper mapper = new ObjectMapper();
GenreDeserializer deserializer = new GenreDeserializer();
SimpleModule module = new SimpleModule();
module.addDeserializer(Genre.class, deserializer);
mapper.registerModule(module);
Genre genre = mapper.readValue(JSON_FILE, Genre.class);
System.out.println(genre);
genre = mapper.readValue(JSON_FILE, Genre.class);
System.out.println(genre);
}
static final File JSON_FILE = new File("json.json");
}
該模型
public class Genre {
public String id;
public String name;
public String url;
public RssUrls rssUrls;
public ChartUrls chartUrls;
@Override
public String toString() {
return "Category{" + "id=" + id + ", name="
+ name + ", url=" + url + ", rssUrls=" + rssUrls + '}';
}
public static class RssUrls {
public String topVideoPodcastEpisodes;
public String topAudioPodcasts;
public String topVideoPodcasts;
public String topPodcasts;
public String topAudioPodcastEpisodes;
public String topPodcastEpisodes;
@Override
public String toString() {
return "RssUrls{" + "topVideoPodcastEpisodes=" + topVideoPodcastEpisodes
+ ", topAudioPodcasts=" + topAudioPodcasts
+ ", topVideoPodcasts=" + topVideoPodcasts
+ ", topPodcasts=" + topPodcasts
+ ", topAudioPodcastEpisodes=" + topAudioPodcastEpisodes
+ ", topPodcastEpisodes=" + topPodcastEpisodes + '}';
}
}
public static class ChartUrls {
public String videoPodcastEpisodes;
public String podcasts;
public String audioPodcastEpisodes;
public String audioPodcasts;
public String podcastEpisodes;
public String videoPodcasts;
@Override
public String toString() {
return "ChatUrls{" + "videoPodcastEpisodes=" + videoPodcastEpisodes
+ ", podcasts=" + podcasts
+ ", audioPodcastEpisodes=" + audioPodcastEpisodes
+ ", audioPodcasts=" + audioPodcasts
+ ", podcastEpisodes=" + podcastEpisodes
+ ", videoPodcasts=" + videoPodcasts + '}';
}
}
}
要在JAX-RS中配置ObjectMapper
,您可以查看這篇文章
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