Libraries and Samples–Google APIs Java Client

Check this link

Getting Started with YouTube Java API

See example

YouTube Data API - Java Code Samples

Check the documentation here

package com.google.api.services.samples.youtube.cmdline.youtube_cmdline_channelbulletin_sample;

import java.io.File;
import java.util.Calendar;
import java.util.List;

import com.google.api.client.auth.oauth2.Credential;
import com.google.api.client.extensions.java6.auth.oauth2.AuthorizationCodeInstalledApp;
import com.google.api.client.extensions.java6.auth.oauth2.FileCredentialStore;
import com.google.api.client.extensions.jetty.auth.oauth2.LocalServerReceiver;
import com.google.api.client.googleapis.auth.oauth2.GoogleAuthorizationCodeFlow;
import com.google.api.client.googleapis.auth.oauth2.GoogleClientSecrets;
import com.google.api.client.googleapis.json.GoogleJsonResponseException;
import com.google.api.client.http.HttpTransport;
import com.google.api.client.http.javanet.NetHttpTransport;
import com.google.api.client.json.JsonFactory;
import com.google.api.client.json.jackson2.JacksonFactory;
import com.google.api.services.youtube.YouTube;
import com.google.api.services.youtube.model.Activity;
import com.google.api.services.youtube.model.ActivityContentDetails;
import com.google.api.services.youtube.model.ActivityContentDetails.Bulletin;
import com.google.api.services.youtube.model.ActivitySnippet;
import com.google.api.services.youtube.model.Channel;
import com.google.api.services.youtube.model.ChannelListResponse;
import com.google.api.services.youtube.model.ResourceId;
import com.google.common.collect.Lists;

/**
 * Creates a video bulletin that is posted to the user's channel feed.
 *
 * @author Jeremy Walker
 */
public class ChannelBulletin {

  /** Global instance of the HTTP transport. */
  private static final HttpTransport HTTP_TRANSPORT = new NetHttpTransport();

  /** Global instance of the JSON factory. */
  private static final JsonFactory JSON_FACTORY = new JacksonFactory();

  /** Global instance of YouTube object to make all API requests. */
  private static YouTube youtube;

  /*
   * Global instance of the video id we want to post as a bulletin into our channel feed. You will
   * probably pull this from a search or your app.
   */
  private static String VIDEO_ID = "L-oNKK1CrnU";

  /**
   * Authorizes the installed application to access user's protected data.
   *
   * @param scopes list of scopes needed to run upload.
   */
  private static Credential authorize(List scopes) throws Exception {

    // Load client secrets.
    GoogleClientSecrets clientSecrets = GoogleClientSecrets.load(
        JSON_FACTORY, ChannelBulletin.class.getResourceAsStream("/client_secrets.json"));

    // Checks that the defaults have been replaced (Default = "Enter X here").
    if (clientSecrets.getDetails().getClientId().startsWith("Enter")
        || clientSecrets.getDetails().getClientSecret().startsWith("Enter ")) {
      System.out.println(
          "Enter Client ID and Secret from https://code.google.com/apis/console/?api=youtube"
          + "into youtube-cmdline-channelbulletin-sample/src/main/resources/client_secrets.json");
      System.exit(1);
    }

    // Set up file credential store.
    FileCredentialStore credentialStore = new FileCredentialStore(
        new File(System.getProperty("user.home"), ".credentials/youtube-api-channelbulletin.json"),
        JSON_FACTORY);

    // Set up authorization code flow.
    GoogleAuthorizationCodeFlow flow = new GoogleAuthorizationCodeFlow.Builder(
        HTTP_TRANSPORT, JSON_FACTORY, clientSecrets, scopes).setCredentialStore(credentialStore)
        .build();

    // Build the local server and bind it to port 8080
    LocalServerReceiver localReceiver = new LocalServerReceiver.Builder().setPort(8080).build();

    // Authorize.
    return new AuthorizationCodeInstalledApp(flow, localReceiver).authorize("user");
  }

  /**
   * Authorizes user, runs Youtube.Channnels.List to get the default channel, and posts a bulletin
   * with a video id to the user's default channel.
   *
   * @param args command line args (not used).
   */
  public static void main(String[] args) {

    // Scope required to upload to YouTube.
    List scopes = Lists.newArrayList("https://www.googleapis.com/auth/youtube");

    try {
      // Authorization.
      Credential credential = authorize(scopes);

      // YouTube object used to make all API requests.
      youtube = new YouTube.Builder(HTTP_TRANSPORT, JSON_FACTORY, credential).setApplicationName(
          "youtube-cmdline-channelbulletin-sample").build();

      /*
       * Now that the user is authenticated, the app makes a channel list request to get the
       * authenticated user's channel. https://developers.google.com/youtube/v3/docs/channels/list
       */
      YouTube.Channels.List channelRequest = youtube.channels().list("contentDetails");
      channelRequest.setMine("true");
      /*
       * Limits the results to only the data we need making your app more efficient.
       */
      channelRequest.setFields("items/contentDetails");
      ChannelListResponse channelResult = channelRequest.execute();

      /*
       * Gets the list of channels associated with the user.
       */
      List channelsList = channelResult.getItems();

      if (channelsList != null) {
        // Gets user's default channel id (first channel in list).
        String channelId = channelsList.get(0).getId();

        /*
         * We create the snippet to set the channel we will post to and the description that goes
         * along with our bulletin.
         */
        ActivitySnippet snippet = new ActivitySnippet();
        snippet.setChannelId(channelId);
        Calendar cal = Calendar.getInstance();
        snippet.setDescription("Bulletin test video via YouTube API on " + cal.getTime());

        /*
         * We set the kind of the ResourceId to video (youtube#video). Please note, you could set
         * the type to a playlist (youtube#playlist) and use a playlist id instead of a video id.
         */
        ResourceId resource = new ResourceId();
        resource.setKind("youtube#video");
        resource.setVideoId(VIDEO_ID);

        Bulletin bulletin = new Bulletin();
        bulletin.setResourceId(resource);

        // We construct the ActivityContentDetails now that we have the Bulletin.
        ActivityContentDetails contentDetails = new ActivityContentDetails();
        contentDetails.setBulletin(bulletin);

        /*
         * Finally, we construct the activity we will write to YouTube via the API. We set the
         * snippet (covers description and channel we are posting to) and the content details
         * (covers video id and type).
         */
        Activity activity = new Activity();
        activity.setSnippet(snippet);
        activity.setContentDetails(contentDetails);

        /*
         * We specify the parts (contentDetails and snippet) we will write to YouTube. Those also
         * cover the parts that are returned.
         */
        YouTube.Activities.Insert insertActivities =
            youtube.activities().insert("contentDetails,snippet", activity);
        // This returns the Activity that was added to the user's YouTube channel.
        Activity newActivityInserted = insertActivities.execute();

        if (newActivityInserted != null) {
          System.out.println(
              "New Activity inserted of type " + newActivityInserted.getSnippet().getType());
          System.out.println(" - Video id "
              + newActivityInserted.getContentDetails().getBulletin().getResourceId().getVideoId());
          System.out.println(
              " - Description: " + newActivityInserted.getSnippet().getDescription());
          System.out.println(" - Posted on " + newActivityInserted.getSnippet().getPublishedAt());
        } else {
          System.out.println("Activity failed.");
        }

      } else {
        System.out.println("No channels are assigned to this user.");
      }
    } catch (GoogleJsonResponseException e) {
      e.printStackTrace();
      System.err.println("There was a service error: " + e.getDetails().getCode() + " : "
          + e.getDetails().getMessage());

    } catch (Throwable t) {
      t.printStackTrace();
    }
  }
}

YouTube Data API–Getting Started

Check this documentation

OAuth 2.0 Authorization for YouTube API

Check the documentation here

YouTube player for Websites

Check this link – for developers