java - Retrofit - Multipart Form with image upload and string array -

i creating android app using retrofit 2.0 send post request server. request allow user create group has name, array of users, , image. using multipart form in request because app uploads image server in form of file.

this presenter, given fields needed request.

 public void submitgroup(@nonnull final string accesstoken,                         @nonnull final string userid,                         @nonnull final string groupname,                         @nonnull final string groupiconuri,                         @nullable final string[] members) {       file file = new file(groupiconuri);       requestbody requestowner =             requestbody.create(                     mediatype.parse("multipart/form-data"), userid);     requestbody requestgroupname =             requestbody.create(                     mediatype.parse("multipart/form-data"), groupname);    /**    * requestmembers string[] containing member     * id.  field having trouble     * making requestbody for.    **/     requestbody requestmembers =             requestbody.create(                     mediatype.parse("multipart/form-data"),                                          string.valueof(members));     multipartbody.part filepart =             multipartbody.part                     .createformdata("image", file.getname(),                             requestbody.create(                               mediatype.parse("image/*"), file));       log.e(tag, "accesstoken: " + accesstoken);     log.e(tag, "userid: " + userid);     log.e(tag, "groupname: " + groupname);     log.e(tag, "groupiconuri: " + groupiconuri);     // log.e(tag, "members: " + members);      call<group> call = service.creategroup(accesstoken,                                          requestgroupname,                                          requestowner,                                          filepart);     call.enqueue(this);   } 

here application service class, have run , has worked without including string[] field members.

public interface service { @multipart @post("/group") call<group> creategroup(@header("authorization") string authorization,                         @part("name") requestbody groupname,                         @part("owner") requestbody ownerid,                         @part multipartbody.part file); 

here group class json being serialized to:

public class group { @nonnull @serializedname("name") private string name; @nonnull @serializedname("owner") private object owner; @nonnull @serializedname("image") private string image_name; @nonnull @serializedname("pin") private int pin; @nonnull @serializedname("created_at") private date created_at; @nullable @serializedname("users") private object[] users; @nullable @serializedname("pending_users") private object[] pending_users;  public group(@nonnull final string name,              @nonnull final object owner,              @nullable final object[] users,              @nullable final object[] pending_users,              @nonnull final string image_name,              @nonnull final date created_at,              @nonnull final int pin) {     this.name = name;     this.owner = owner;     this.users = users;     this.pending_users = pending_users;     this.image_name = image_name;     this.created_at = created_at;     this.pin = pin; }  @nonnull public date getcreated_at() {     return created_at; } @nonnull public string getname() {     return name; } @nonnull public object getowner() {     return owner; } @nonnull public int getpin() {     return pin; }  public object getusers() {     return users; }  public object getpending_users() {     return pending_users; }  public string getimage_name() {     return image_name; } 

my questions are:

1. how can create send member string[] requestbody? have read can hashmapped, way?
2. is necessary have groupname , ownerid typecasted requestbody? can send @part string?