How do I retrieve durations of videos through Youtube API v3 YouTube.PlaylistItems.List request?

I'm using Youtube API v3 (Java) to access Youtube videos, playlists. Below is a sample code:

YouTube.PlaylistItems.List request = 
youtube.playlistItems().list("id,contentDetails,snippet");
request.setPlaylistId(/*playlist id*/);                
request.setFields("items(contentDetails/videoId,snippet/title,snippet/publishedAt, 
snippet/description),nextPageToken,pageInfo");

PlaylistItemListResponse result = request.execute();

Now I can get a title of each video from a playlist like this:

for (PlaylistItem item : result.getItems()) {
    item.getSnippet().getTitle();
    // But how can I retrieve a duration now?
}

I have tried different methods to retrieve duration of the videos, but they all returned null. How do I get a duration?

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  for (Video playlistItem : playlistItemList) {
    YouTubeData map = new YouTubeData();

    map.mVideo = playlistItem.getId();
    map.mDuration = Utils.durationToDuration((String) playlistItem.getContentDetails()
        .get("duration"));
    map.mTitle = playlistItem.getSnippet().getTitle();
    map.mDescription = Utils.condenseWhiteSpace(playlistItem.getSnippet().getDescription());
    map.mThumbnail = thumbnailURL(playlistItem.getSnippet().getThumbnails());
    map.mPublishedDate = playlistItem.getSnippet().getPublishedAt().getValue();

    result.add(map);
  }

Video duration can be found inside contentDetails part of .videos().list(). Unfortunatelly, you can get video duration through PlayListItem as in your example, you can get only video_id.

So, you can extract all video_id that playlist has and make an additional call to receive video data, like:

https://www.googleapis.com/youtube/v3/videos?id=9bZkp7q19f0&part=contentDetails&key={YOUR_API_KEY}

as a result, you will get something like:

"contentDetails": {
    "duration": "PT4M13S",
    "dimension": "2d",
    "definition": "hd",
    "caption": "false",
    "licensedContent": true,
    "regionRestriction": {
     "blocked": [
      "DE"
     ]
 }

There is a field duration inside.

You can play with all YouTube API here