New thumbnail feature - how to use in Java - google-drive-api

Question

I'd like to leverage the new thumbnail feature of Google Drive using the latest Java SDK.
But all I get is a bad request response.
Can someone post a working example of this feature?
I've been simply setting the mimetype and Base64-encoded image data but this does not work - at least for file.insert and file.patch.
Update:
This is my (simplified) code snippet. It works fine without the new thumbnail stuff - and the encoded image data looks ok as well:
...
Drive drive = getDrive(account);
File file = new File();
file.setTitle(name);
...
HTTPResponse response = urlFetch.fetch(new URL(imageUrl));
String encodedImage = new String(Base64.encodeBase64(response.getContent()));
Thumbnail thumbnail = new Thumbnail();
thumbnail.setImage(encodedImage);
thumbnail.setMimeType("image/png");
file.setThumbnail(thumbnail);
file = drive.files().insert(file).execute();
This is the response:
com.google.api.client.googleapis.json.GoogleJsonResponseException: 400 OK
{
"code" : 400,
"errors" : [ {
"domain" : "global",
"message" : "Bad Request",
"reason" : "badRequest"
} ],
"message" : "Bad Request"
}
at com.google.api.client.googleapis.json.GoogleJsonResponseException.from(GoogleJsonResponseException.java:143)
at com.google.api.client.googleapis.json.GoogleJsonResponseException.execute(GoogleJsonResponseException.java:187)
at com.google.api.client.googleapis.services.GoogleClient.executeUnparsed(GoogleClient.java:279)
at com.google.api.client.http.json.JsonHttpRequest.executeUnparsed(JsonHttpRequest.java:207)

Answer 1

The thumbnail image needs to be encoded as a Base64 UrlSafe String.
Using
String encodedImage = Base64.encodeBase64URLSafeString(response.getContent());
to encode the image fixed the issue.