Translating curl to Java

Question

I need to catch an output of a post call to a rest service that uploads a file from Java code . The only information I have about this service is a curl command:

curl -u "username:token" \
-X POST "https://host.name.to/upload/upload" \
-F "file=@/path/to/app/fileToUpload"

So far, apart from successfully executing the curl-command, I've also successfully made the rest call through Postman

I have tried to translate the call to OkHttp as well as tried to just run the call through Java's Process api but without luck.

When I tried to let OkHttp call the service I get error 422 (even when just copy and pasting the code snippet straight from Postman)

When I try to execute curl though Process(), curl exits with code 1

Trying to call rest service using okHttp:

RequestBody requestBody = new MultipartBody.Builder()
        .setType(MultipartBody.FORM)
        .addFormDataPart("file", fileLocationAsString)
        .build();

Request requestWithHeader = new Request.Builder()
        .header("Authorization", Credentials.basic(userName, accessKey))
        .header("Content-Type","multipart/form-data ")
        .header("cache-control", "no-cache")
        .header("Content-Disposition",  "form-data; name=\"file\"; filename=" + fileLocationAsString)
        .url("https://host.name.to/upload/upload")
        .post(requestBody)
        .build();
try {
    Response response = client.newCall(requestWithHeader).execute();
    uploadAppFileResponse = (JSONObject) parser.parse(response.body().string());
} catch (IOException e) {
    e.printStackTrace();
} catch (ParseException e) {
    e.printStackTrace();
}

Trying to execute curl through Process:

String command = "/usr/bin/curl -u " + userName + ":" + accessKey + " -X POST \"https://host.name.to/upload\" -F file=@" + fileLocationAsString;
try {
    Process process = Runtime.getRuntime().exec(command);
    process.waitFor();
    int exitValue = process.exitValue();
    System.out.println(exitValue);
} catch (IOException | InterruptedException e) {
    e.printStackTrace();
}

I would like to be able to successfully execute the upload, preferably through a clean service call instead of running curl through Process() and to catch the (json) response.

Thanks in advance