我坚持在android中实现以下功能实际上我在android新api（api29）方面没有太多的工作经验
1-从gallery中挑选视频，它给了我uri，我根据这个线程创建了iputestreamrequestbody
这是我的代码：

public class InputStreamRequestBody extends RequestBody {

private final MediaType contentType;
private final ContentResolver contentResolver;
private final Uri uri;

public InputStreamRequestBody(MediaType contentType, ContentResolver contentResolver, Uri uri) {
    if (uri == null) throw new NullPointerException("uri == null");
    this.contentType = contentType;
    this.contentResolver = contentResolver;
    this.uri = uri;
}

@Nullable
@Override
public MediaType contentType() {
    return contentType;
}

@Override
public long contentLength() {
    return -1;
}

@Override
public void writeTo(@NonNull BufferedSink sink) throws IOException {
    try (Source source = Okio.source(contentResolver.openInputStream(uri))) {
        sink.writeAll(source);
    }
}

}
步骤：3-这是我的改装代码：

public interface PlatformGroupPostService {

@Multipart
@POST("brainy/api/v0/post")
Observable<NewGroupAPIResponse> createPost(@Part("postData") RequestBody postData,
                                           @Part MultipartBody.Part attachments);

}
请求以空文件示例命中服务器这里是我的rest调用：

//attachments always coming null
    public ResponseEntity<?> createPost(@RequestParam String postData,
                                        @RequestPart(value = "attachments", required = false)
                                                MultipartFile attachments) {
        PostEntity postEntity = getPostEntity(postData);
        return new ResponseEntity<>(postService.createPost(postEntity, attachments), HttpStatus.CREATED);
    }

上面的restapi可以很好地处理postman请求，但是从改型调用来看它不起作用。我想我做错了什么。
我正在努力实现这个功能，因为4-5天，应用多种解决方案，如
1-将android文件从gallery存储到缓存，然后尝试上载，但问题相同。现在对我来说有点过分了

fun prepareFilePart(partName: String, uri: Uri, context: Context, name: String): MultipartBody.Part {
    val inputStream = context.contentResolver.openInputStream(uri)
    val file = File(context.cacheDir, name+".mp4")
    val fos = FileOutputStream(file)

    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {
        if (inputStream != null) {
            FileUtils.copy(inputStream, fos)
        }
    } else {

    }

    fos.flush();
    fos.getFD().sync();
    fos.close();
    val requestBody: RequestBody =
            RequestBody.create(MediaType.parse(context.contentResolver.getType(uri)), file)
    return MultipartBody.Part.createFormData(partName, name, requestBody)
}

任何帮助都是值得赞赏的