MrEngineer13 MrEngineer13 - 8 months ago 26
JSON Question

How to structure a Map from Json that has duplicate keys

Ok so I have this piece of JSON that I want to parse with Gson. I would like the Strings to be the values and the longs to be the keys.


The issue is the data type, when I try a
Map<String, Long>
it parses everything but gives me an error because of the duplicate String keys.

I tried to reverse it thinking Gson would know to switch them around but when I tried
Map<Long, String>
I got an error about not being able to parse my Strings as Longs.

To get it to work I created a swap map class that takes the Key and Value types and swaps them like so
public class SwapMap<K, V> implements Map<K, V>
however translating the swapped map actions like put/get/remove seem to be pretty difficult to make work.

What's the best way to parse this with Gson even though the strings aren't unique? (But the numbers are)


So what I did is just made a custom Gson Deserializer that mapped these values to a LongSparseArray<String>, which is the best way to go about it.

This is the relevant parts of the Deserializer:

for (JsonElement array : jsonObject.get("my_key").getAsJsonArray()) {
    if (array.getAsJsonArray().size() == 2) {
      String value = array.getAsJsonArray().get(VALUE).getAsString();
      long key = array.getAsJsonArray().get(KEY).getAsLong();
      progress.completedActivities.put(key, value);

Then I just added it to my Gson creator like so:

@Provides @Singleton Gson provideGson() {
return new GsonBuilder()
    .registerTypeAdapter(MyClass.class, new MyClass())