Retrofit — Multiple query parameters of same name where name is set dynamically

You can use an arrayList! Something like the code below.

@GET(value = "products/search")
Single<ProductSearchResponse> productSearch(
    @Query("status") List<Integer> status
);


ArrayList<Integer> queryStatus = new ArrayList<>();
queryStatus.add(0);
queryStatus.add(1);
queryStatus.add(2);

productService.productSearch(queryStatus);

Your url will be like that -> {url}?status=0&status=1&status=2

Thanks to the link, posted by @ILLIA DEREVIANKO (https://github.com/square/retrofit/issues/1324), I've managed to solve the problem with this class:

   public class ProxyRetrofitQueryMap extends HashMap<String, Object> {
    public ProxyRetrofitQueryMap(Map<String, Object> m) {
        super(m);
    }

    @Override
    public Set<Entry<String, Object>> entrySet() {
        Set<Entry<String, Object>> originSet = super.entrySet();
        Set<Entry<String, Object>> newSet = new HashSet<>();

        for (Entry<String, Object> entry : originSet) {
            String entryKey = entry.getKey();
            if (entryKey == null) {
                throw new IllegalArgumentException("Query map contained null key.");
            }
            Object entryValue = entry.getValue();
            if (entryValue == null) {
                throw new IllegalArgumentException(
                        "Query map contained null value for key '" + entryKey + "'.");
            }
            else if(entryValue instanceof List) {
                for(Object arrayValue:(List)entryValue)  {
                    if (arrayValue != null) { // Skip null values
                        Entry<String, Object> newEntry = new AbstractMap.SimpleEntry<>(entryKey, arrayValue);
                        newSet.add(newEntry);
                    }
                }
            }
            else {
                Entry<String, Object> newEntry = new AbstractMap.SimpleEntry<>(entryKey, entryValue);
                newSet.add(newEntry);
            }
        }
        return newSet;
    }
}

With this we can just use a map, where key is a unique parameter name and value is a List of Strings, that are values for this parameter. Something like this:

ProxyRetrofitQueryMap map = new ProxyRetrofitQueryMap();

    List<String> values1 = new ArrayList<>();
    values1.add("10");
    values1.add("11");
    map.put("filter[1]", values1);

    List<String> values2 = new ArrayList<>();
    values1.add("20");
    values1.add("21");
    map.put("filter[2]", values2);

You can use @QueryMap annotation like this:

public interface NewsService() {  
    @GET("/news")
    Call<List<News>> getNews(
        @QueryMap Map<String, String> options
    );
}

Map<String, String> data = new HashMap<>();
data.put("author", "Marcus");
data.put("page", String.valueOf(2));

...
newsService.getNews(data);

More details: https://futurestud.io/tutorials/retrofit-2-add-multiple-query-parameter-with-querymap