Gson calls returns empty objects over multiple classes

问题

I'm trying to serialize to serialize the json string I have included below.

 {
        "mood": {
            "is_featured": true,
            "description": null,
            "title": "2014 ",
            "ordering": null,
            "is_recently_modified": true,
            "is_test": false,
            "tracks": [

            {
                "album": {
                    "release_date": "2014-11-06",
                    "id": 359778,
                    "name": "Amansız Gücenik"
                },
                "name": "Hırpalandı Mayıs",
                "artist": {
                    "id": 491169,
                    "name": "Ceylan Ertem"
                },
                "duration": 227,
                "isrc": "TRA161400207",
                "id": 3903997
            },
            {
                "album": {
                    "release_date": "2013-08-05",
                    "id": 329129,
                    "name": "For Fuld Musik - 25 Danske Sommer Pop & Rock Hits Vol. 2"
                },
                "name": "Am I Wrong",
                "artist": {
                    "id": 755957,
                    "name": "Nico & Vinz"
                },
                "duration": 387,
                "isrc": "NO2G31301011",
                "id": 3655085
            }
        ],
        "image_url": "some_url",
        "is_recently_created": true,
        "id": 128
    }
}

I'm using this gson call to serialize it

Mood mood = new Gson().fromJson(result, Mood.class);

My class structers are like this.

public class Mood {

    private boolean is_featured;
    private boolean is_recently_modified;
    private boolean is_recently_created;
    private boolean is_test;


    private String  description;
    private String  title;
    private String  image_url;

    private int     id;
    private int     ordering;

    private Track[] tracks;



    public static class MoodContainer {
        public Mood[] moods;
    }


}


public class Track {

    //variables
    private Album       album;
    private Artist      artist;
    private Provider    provider;


    private String      secure_url;
    private String      name;
    private String      region;
    private String      isrc;

    private int         duration;
    private int         track_order;
    private int         id;

}

And it goes on like this for any additional class variable. When I try to use the above call I end up with objects that have all null values. One thing to notice is some fields are not supplied in json string because different api calls supply different parts of these json strings. What I am doing wrong?

回答1:

Root JSON object you provided has property mood - so you either have two options for deserialization to work properly:

Wrap your Mood class inside another object like this:

public class MoodWrapper { private Mood mood; }

and change de-serialization code to

MoodWrapper moodWrapper = new Gson().fromJson(result, MoodWrapper.class);

Skip a root object when deserializing:

final Gson gson = new Gson();
JsonParser parser = new JsonParser();
JsonObject rootObj = parser.parse(json).getAsJsonObject();
Mood mood = gson.fromJson(rootObj.getAsJsonObject("mood"), Mood.class);

回答2:

The top-level elements in the JSON string should be your object's properties, not the outer element "mood" which you have.

来源：https://stackoverflow.com/questions/27627277/gson-calls-returns-empty-objects-over-multiple-classes

标签

java

json

gson