RestDeserializer.java

package com.banasiak.android.example.api.parser;

import com.google.gson.Gson;
import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonParseException;

import java.lang.reflect.Type;

/**
 * All API responses are returned in the following format:
 *   {
 *     "data": {
 *         // HTTP 200 data object
 *     },
 *     "error": {
 *         // HTTP 4xx/5xx error object
 *     }
 *   }
 * This custom Gson type adapter can be registered for generic response objects and handles
 * deserializing the response into the appropriate object typing depending on the key specified in
 * the constructor.
 *
 * @param <T> the class to deserialize the JSON string as
 */
public class RestDeserializer<T> implements JsonDeserializer<T> {

    public static final String DATA = "data";

    public static final String ERROR = "error";

    private String key;

    /**
     * Custom Gson type adapter for deserializing JSON objects inside a REST data/error wrapper.
     * @param key the key to deserialize (i.e. "data" or "error")
     */
    public RestDeserializer(String key) {
        this.key = key;
    }

    @Override
    public T deserialize(JsonElement je, Type type, JsonDeserializationContext jdc)
            throws JsonParseException {
        JsonElement content = je.getAsJsonObject().get(key);
        return new Gson().fromJson(content, type);
    }
}