JSON parse single string to object

Question

is there any easy way to to convert this json:

{
    ...,
    "pictures": [
        "url1",
        "url2"
    ],
    ...
}

to

List<Picture> pictures

where Picture is:

class Picture{
      String url;
}

It won't work as above, because I have an exception, saying

Expected BEGIN_OBJECT but was STRING

A quick fix depending on your use of the object could be to put @JsonValue above the getter for your String url. — Zircon
– Zircon, Commented Jul 14, 2016 at 15:40
@Zircon Wrong library. Also, that would only be useful for serializing. — Sotirios Delimanolis
– Sotirios Delimanolis, Commented Jul 14, 2016 at 15:47

Laurel · Accepted Answer · 2016-07-14 18:47:11Z

1

You need to implement a custom deserializer for this. Should be looking like this (I didn't try to execute, but that should give you the idea where to start, presumably you have a public constructor with String argument in your Picture.class)

private class PictureDeserializer implements JsonDeserializer<Picture> {
  public Picture deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)
      throws JsonParseException {
    return new Picture(json.getAsJsonPrimitive().getAsString());
  }
}

It should be registered:

GsonBuilder gson = new GsonBuilder();
gson.registerTypeAdapter(Picture.class, new PictureDeserializer());

edited Jul 14, 2016 at 18:47

Laurel

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answered Jul 14, 2016 at 15:42

Battle_Slug

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3 Comments

PaleNisko Over a year ago

I know deserializer method to do this thing, is there any other way to avoid making deserializer?

Battle_Slug Over a year ago

@PaleNisko Then you should mention it in the question to avoid making people to waist time. Anyway, the answer: I don't think so. The mapper contains a predefined set of actions mapped to the most generic types/classes on one-to-one relationship basis (simplified). Going through JSON tree, the mapper encounters different types/classes and deserializes them accordingly. E.g. single string is mapped to the String.class out-of-box. If you have a custom Picture.class, the mapper just cannot have the consistent mapping out-of-box as its developers couldn't keep in mind all classes in the world.

PaleNisko Over a year ago

Ok, thank you for your feedback i will keep in mind your advice. Know I understand why it is done like that!

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