Deserializing JSON array containing objects with an array using GSON

Question

I have a JSON response representing a Band that looks like this:

[
 {
  "Picture": {
  "Small": "someurl
  "Medium": "someurl",
  "Large": "someurl",
  "XLarge": "someurl"
},
"Name": "Tokyo Control Tower",
"Guid": "TCT",
"ID": 15
 }
]

And I'm trying to use GSON to deserialize it into a class called SearchResults which contains a list of Bands. My SearchResults and Band classes look like this:

public class SearchResults {
    public List<Band> results;
}

public class Band {
    @SerializedName("Name")
    public String name;

    @SerializedName("Guid")
    public String guid;

    @SerializedName("ID")
    public Integer id;

    @SerializedName("Picture")
    List<Photo> pictures;

}

In my code I try to convert the json string like this:

protected void onPostExecute(String result) {
        Gson gson = new Gson();
        SearchResults results = gson.fromJson(result, SearchResults.class);
        Band band = results.results.get(0);
        bandName.setText(band.name);
    }

When I run this code, I get an error from GSON saying Expected BEGIN_OBJECT but was BEGIN_ARRAY. Any ideas on how to fix?

pictures is a list in your class definition (i.e. a JSON array), but it's a JSON object in the sample JSON you gave. Did you meant to either make it an array in the JSON, or create a "Pictures" class or map to represent the various picture sizes? — Jeremy Roman
– Jeremy Roman, Commented Aug 22, 2013 at 0:15

Brian Roach · Accepted Answer · 2013-08-22 16:04:11Z

3

You have a couple issues.

First and foremost, what is causing the error you post is that you are telling Gson that your JSON represents an object (SearchResults) when it doesn't; your JSON is an array of objects (specifically, an object you're mapping to your Java Band class).

The correct way to do this is via:

Type collectionType = new TypeToken<Collection<Band>>(){}.getType();
Collection<Band> bands = gson.fromJson(jsonString, collectionType);

Once you do that you're going to have a problem in that in your Java class you're saying that "Picture" in your JSON is an array of Photo objects when in fact it's not; it's a single object.

answered Aug 22, 2013 at 16:04

Brian Roach

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