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GSON - Deserialize primitive array

Consider this simple Json:

{
    "test": [
        0,
        3
    ]
}

Now I want to deserialize it in a simple int array, so for this I use a custom deserializer:

class ArrayDeserializer implements JsonDeserializer<int[]> {
    @Override
    public int[] deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
        return context.deserialize(json.getAsJsonObject().getAsJsonArray("test"), int[].class);
    }
}

and then:

Gson gson = new GsonBuilder().registerTypeAdapter(int[].class, new ArrayDeserializer()).create();
int[] arr = gson.fromJson(json, int[].class);

which throws:

Exception in thread "main" com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Not a JSON Object: [0,3]

However, when I do this:

class ArrayDeserializer implements JsonDeserializer<int[]> {

    private static final Gson gson = new Gson();

    @Override
    public int[] deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
        return gson.fromJson(json.getAsJsonObject().getAsJsonArray("test"), int[].class);
    }
}

It works, and I get the expected result. Why?

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2 answers

Rewrite ArrayDeserializerin equivalent form, but more expressive

class ArrayDeserializer implements JsonDeserializer<int[]> {
    @Override
    public int[] deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
        JsonArray jsonArray = json.getAsJsonObject().getAsJsonArray("test");
        return context.deserialize(jsonArray, int[].class);
    }
}

JsonDeserializationContext#deserializeJavadoc state

. , JsonDeserializer.deserialize(JsonElement, Type, JsonDeserializationContext). , Gson .

, , , , stackoverflow .

?

( )

deserialize {test:[0,3]} as int[]
// --> Gson finds ArrayDeserializer mapped to int[]
take given JSON as an object (OK), extract 'test' as JSON array (OK)
deserialize [0,3] as int[]
// --> Gson finds ArrayDeserializer mapped to int[]
take given JSON as an object (FAIL)

, , JSON JSON, ArrayDeserializer JSON.

return gson.fromJson(json.getAsJsonObject().getAsJsonArray("test"), int[].class);

"test" JSON Gson, ArrayDeserializer.

new Gson().fromJson("[0,3]", int[].class);

int[] 0 3. .

.

POJO

class Pojo {
    private int[] test;
    public int[] getTest() {
        return test;
    }
    public void setTest(int[] test) {
        this.test = test;
    }
}


Pojo pojo = new Gson().fromJson(json, Pojo.class);
int[] arr = pojo.getTest(); 


Gson gson = new Gson();
JsonArray jsonArray = gson.toJsonTree(json).getAsJsonObject().get("test").getAsJsonArray();
int[] arr = gson.fromJson(jsonArray, int[].class);
+3

, ArrayDeserializer:

class ArrayDeserializer implements JsonDeserializer<int[]> {
    @Override
    public int[] deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
        return context.deserialize(json.getAsJsonObject().getAsJsonArray("test"), int[].class);
    }
}

deserialize deserialize, ... IllegalStateException.

int[] ( ), . gson.fromJson , fromJson int[]. , .

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