How to convert Map<String, String> to RequestBody?

Question

Using Retrofit 2.4.0, I am making a @Multipart @POST request. I am sending a file as @Part along with some metadata as@PartMap. This is what the call looks like.

@Multipart
@POST("https://8hoot.com/my-path")
Single<Response<UploadMediaResponseModel>> uploadMedia(
        @PartMap Map<String, RequestBody> metadata,
        @Part MultipartBody.Part filePart
);

There is another Map<String, String>, let us call it subMetaMap, which contains related key-value pairs.

How can I store this subMetaMap in the @PartMap metadata? Something like shown below.

RequestBody subMetaMapAsRequestBody; // Convert subMetaMap to RequestBody
metadata.put("subMeta", subMetaMapAsRequestBody);

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Currently, I am using the following method.

for (String s : subMetaMap.keySet()) {
    RequestBody requestBody = RequestBody.create(MultipartBody.FORM, subMetaMap.get(s));
    metadata.put(s, requestBody);
}

This is not the desired solution as I want the whole subMetaMap as the RequestBody not its individual key-value pairs

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Edit 1- The backend team doesn't take different MIME types during Multipart request. So sending JSON, MessagePack, etc. is not an option.

Answer 1

Let's assume you have following map you want to send this data to retrofit request body

HashMap<String, String> map = new HashMap<>();
map.put("key1", "value1");
map.put("key2", "value2");
map.put("key3", "value3");
map.put("key4", "value4");

Following is the URL Request method:

@FormUrlEncoded
@POST("/yourapiname")
Call<ResponseObj> methodName(@FieldMap HashMap<String, String> yourHasMapObject);

If you want to add file and hashmap then use the following method:

@Multipart
@POST("yourapiname")
Call<ResponseObj> methodName(@HeaderMap HashMap<String, String> yourHasMapObject, @Part MultipartBody.Part file);