Question

我在我的项目中使用Jackson来解析从服务器收到的JSON，解析步骤非常好，在尝试使用嵌套对象时会出现问题。这是一些代码：

@JsonIgnoreProperties(ignoreUnknown = true)
public class Song {

    @JsonProperty("id")
    private int id = 0;
    @JsonProperty("title")
    private String title = "";
    @JsonProperty("link")
    private String link = "";
    @JsonProperty("album")
    private Album album;

    public Song() {
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getLink() {
       return link ;
    }

    public void setLink(String link ) {
        this.link = link ;
    }

    public Album getAlbum() {
        return album;
    }

    public void setAlbum(Album album) {
        this.album = album;
    }
}

Album类看起来像这样：

@JsonIgnoreProperties(ignoreUnknown = true)
public class Album {

    @JsonProperty("id")
    private int id;
    @JsonProperty("title")
    private String title;
    @JsonProperty("artist")
    private Artist artist;

    public Album(){}

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title){
        this.title = title;
    }

    public Artist getArtist() {
        return artist;
    }

    public void setArtist(Artist artist) {
        this.artist = artist;
    }
}

最后是“艺术家”课程：

@JsonIgnoreProperties(ignoreUnknown = true)
public class Artist{

    @JsonProperty("id")
    private int id;
    @JsonProperty("name")
    private String name;

    public Artist() {
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

所以，正如我在JSON解析之前所说的那样，问题是当我尝试访问其中一个“子”对象时，如果我试图获取艺术家名称。当我这样做时：

getSong().getAlbum().getArtist().getName();

无论我在哪里做，杰克逊停止解析JSON给出：

(IOException)Error: No suitable constructor found for type [simple type, class com.zarpamos.fandanztap.model.Album]: can not instantiate from JSON object (missing default constructor or creator, or perhaps need to add/enable type information?)

普通JSON输出：

{"categories":[{"id":"1","name":"Pop","packs":[{"id":"2","songs":[{"album":{"id":"2","title":"Sex And Love","artist":{"id":"2","name":"Enrique Iglesias"}},"id":"3","title":"Bailando","link":"song_1.mp3"},{"album":{"id":"1","title":"Peace Is The Mission","artist":{"id":"3","name":"Major Lazer"}},"id":"6","title":"Powerful","link":"song_2.mp3"},{"album":{"id":"2","title":"Sex And Love","artist":{"id":"2","name":"Enrique Iglesias"}},"id":"4","title":"Loco","link":"song_3.mp3"}, // More JSON elements...

解析“类别”和“包”非常有效，问题出在“专辑”中。

相同的JSON输出但风格化：

这是堆栈跟踪：

 W/System.err﹕ at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromObjectUsingNonDefault(BeanDeserializerBase.java:1080)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:295)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:142)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:523)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.impl.FieldProperty.deserializeAndSet(FieldProperty.java:101)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.impl.BeanPropertyMap.findDeserializeAndSet(BeanPropertyMap.java:285)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:248)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:136)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:245)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:217)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:25)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:523)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.impl.FieldProperty.deserializeAndSet(FieldProperty.java:101)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.impl.BeanPropertyMap.findDeserializeAndSet(BeanPropertyMap.java:285)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:248)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:136)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:245)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:217)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:25)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:523)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.impl.FieldProperty.deserializeAndSet(FieldProperty.java:101)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.impl.BeanPropertyMap.findDeserializeAndSet(BeanPropertyMap.java:285)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:248)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:136)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:245)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:217)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:25)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:523)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.impl.FieldProperty.deserializeAndSet(FieldProperty.java:101)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.impl.BeanPropertyMap.findDeserializeAndSet(BeanPropertyMap.java:285)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:248)
 W/System.err﹕ at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:136)
 W/System.err﹕ at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:3562)
 W/System.err﹕ at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2578)
 W/System.err﹕ at com.dolphinziyo.myapp.tasks.GetPacksTask.onPostExecute(GetPacksTask.java:93)
 W/System.err﹕ at com.dolphinziyo.myapp.tasks.GetPacksTask.onPostExecute(GetPacksTask.java:38)
 W/System.err﹕ at android.os.AsyncTask.finish(AsyncTask.java:631)
 W/System.err﹕ at android.os.AsyncTask.access$600(AsyncTask.java:177)
 W/System.err﹕ at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
 W/System.err﹕ at android.os.Handler.dispatchMessage(Handler.java:107)
 W/System.err﹕ at android.os.Looper.loop(Looper.java:194)
 W/System.err﹕ at android.app.ActivityThread.main(ActivityThread.java:5371)
 W/System.err﹕ at java.lang.reflect.Method.invokeNative(Native Method)
 W/System.err﹕ at java.lang.reflect.Method.invoke(Method.java:525)
 W/System.err﹕ at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
 W/System.err﹕ at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
 W/System.err﹕ at dalvik.system.NativeStart.main(Native Method)

这真的很奇怪，我不知道我做错了什么。谁能告诉我错误在哪里？

提前谢谢

Answer 1

在Album课程中，您必须拥有Artist属性的设置器，如下所示：

 public void setArtist(Artist artist) {
    this.artist = artist;
 }

不喜欢这样：

 public void setArtist(**Artista** artist) {
    this.artist = artist;
 }

Answer 2

我终于手动解析它，直到我有更多时间来测试它。

Answer 3

您的类是顶级类型还是嵌套在另一个类中？如果他们已经嵌套，您需要将其标记为“静态”

“没有合适的简单类型的构造函数”，Android中的Jackson和另一个

3 个答案: