Jersey API返回的ArrayList與沒有Subclass屬性的對象

Question

使用我的API，我必須返回Object（Playlist），其中有一個ArrayList，其中包含Objects（Track）。

Playlist.java

import javax.xml.bind.annotation.XmlElement; 
import javax.xml.bind.annotation.XmlRootElement; 
import java.util.ArrayList; 
import java.util.Arrays; 

@XmlRootElement 
public class Playlist { 
    private String owner; 
    private String name; 
    private ArrayList<Track> tracks; 

    public Playlist() { 
     this.tracks = new ArrayList<Track>(); 
    } 

    public Playlist(String owner, String name, Track[] tracks) { 
     this.owner = owner; 
     this.name = name; 
     this.tracks = new ArrayList<Track>(Arrays.asList(tracks)); 
    } 

    public void addTrack(Track track) { 
     this.tracks.add(track); 
    } 

    @XmlElement(name = "tracks") 
    public ArrayList<Track> getTracks() { 
     return this.tracks; 
    } 

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

    public String getOwner() { 
     return owner; 
    } 

    public void setOwner(String owner) { 
     this.owner = owner; 
    } 

    public String getName() { 
     return name; 
    } 

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

然而，Track是實際的類的超類使用Song和Video。
在ArrayList中，只找到Song Objects和Video Objects，它們有幾個獨立的屬性。
例如，Song是String:album的一部分，並且Video具有String:description。

的JSON API返回只示出了從Track共享屬性而不是album一個Song屬於或與Video給出的description。

我該如何解決這個問題？

活動

import javax.ws.rs.GET; 
import javax.ws.rs.Path; 
import javax.ws.rs.Produces; 
import javax.ws.rs.core.MediaType; 
import java.util.GregorianCalendar; 

@Path("/api/playlist") 
public class PlaylistActivityREST { 

    @GET 
    @Produces(MediaType.APPLICATION_JSON) 
    public Playlist getPlaylist() { 
     Playlist playlist = new Playlist(
       "Owner", 
       "Playlist name", 
       new Track[]{ 
         new Song(
           "Ed Sheeran", 
           "Galway Girl", 
           "https://www.youtube.com/watch?v=87gWaABqGYs", 
           ((Integer) (60 * 3 + 19)).longValue(), 
           "÷" 
         ), 
         new Video(
           "Ed Sheeran", 
           "Shape of You", 
           "https://www.youtube.com/watch?v=JGwWNGJdvx8", 
           ((Integer) (60 * 4 + 24)).longValue(), 
           25177705, 
           new GregorianCalendar(2017, 5, 3), 
           "÷. Out Now: https://atlanti.cr/yt-album" 
         ) 
       } 
     ); 

     return playlist; 
    } 
} 

Song.java

public class Song extends Track { 

    private String album; 

    public Song(String performer, String title, String url, long duration, String album) { 
     super(performer, title, url, duration); 
     this.album = album; 
    } 

    public String getAlbum() { 
     return album; 
    } 

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

Video.java

public class Video extends Track { 
    private int playCount; 
    private Calendar publicationDate; 
    private String description; 

    public Video(String performer, String title, String url, long duration, int playCount, Calendar publicationDate, String description) { 
     super(performer, title, url, duration); 
     this.playCount = playCount; 
     this.publicationDate = publicationDate; 
     this.description = description; 
    } 

    public int getPlayCount() { 
     return playCount; 
    } 

    public String getPlayCountThousandsSeperator() { 
     return String.format(Locale.US, "%,d", this.playCount).replace(',', '.'); 
    } 

    public void setPlayCount(int playCount) { 
     this.playCount = playCount; 
    } 

    public Calendar getPublicationDate() { 
     return publicationDate; 
    } 

    public void setPublicationDate(Calendar publicationDate) { 
     this.publicationDate = publicationDate; 
    } 

    public String getDescription() { 
     return description; 
    } 

    public void setDescription(String description) { 
     this.description = description; 
    } 
} 

Track.java

@XmlRootElement 
public class Track { 
    private String performer; 
    private String title; 
    private String url; 
    private long duration; 

    public Track() { 
    } 

    public Track(String performer, String title, String url, long duration) { 
     this.performer = performer; 
     this.title = title; 
     this.url = url; 
     this.duration = duration; 
    } 

    public String getPerformer() { 
     return performer; 
    } 

    public void setPerformer(String performer) { 
     this.performer = performer; 
    } 

    public String getTitle() { 
     return title; 
    } 

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

    public String getUrl() { 
     return url; 
    } 

    public void setUrl(String url) { 
     this.url = url; 
    } 

    public long getDuration() { 
     return duration; 
    } 

    public void setDuration(long duration) { 
     this.duration = duration; 
    } 

    public String getParsedDuration() { 
     return this.getDuration()/60 + ":" + this.getDuration() % 60; 
    } 
} 

Answer 1

經過更多小時的研究，我發現this answer，它也適用於這個問題。

現在開始與

@XmlRootElement 
@XmlSeeAlso({Song.class,Video.class}) //This fixed it 
public class Playlist { ... } // Omitting unchanged code