<uses-permission android:name="android.permission.INTERNET"/>

apply plugin: 'com.android.application'

android {
    packagingOptions {
        exclude 'META-INF/DEPENDENCIES'
    }
}

dependencies {
    //생략
    implementation 'com.google.apis:google-api-services-youtube:v3-rev183-1.22.0'
    implementation 'com.google.http-client:google-http-client-android:+'
    implementation 'com.google.api-client:google-api-client-android:+'
    implementation 'com.google.api-client:google-api-client-gson:+'
}

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/btn_search"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="144dp"
        android:layout_marginLeft="144dp"
        android:layout_marginTop="116dp"
        android:text="비디오 검색하기"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/btn_show"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="144dp"
        android:layout_marginLeft="144dp"
        android:layout_marginTop="196dp"
        android:text="비디오 검색결과보기"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <TextView
        android:id="@+id/tv_result"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</android.support.constraint.ConstraintLayout>

public class MainActivity extends AppCompatActivity {
    private String API_KEY = "youtube_api_key";

    private TextView tv_result;
    private String result;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        tv_result = findViewById(R.id.tv_result);

        findViewById(R.id.btn_search).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                YoutubeAsyncTask youtubeAsyncTask = new YoutubeAsyncTask();
                youtubeAsyncTask.execute();
            }
        });

        findViewById(R.id.btn_show).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                tv_result.setText(result);

            }
        });
    }

    private class YoutubeAsyncTask extends AsyncTask<Void, Void, Void> {
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
        }

        @Override
        protected Void doInBackground(Void... voids) {
            try {
                HttpTransport HTTP_TRANSPORT = new NetHttpTransport();
                final JsonFactory JSON_FACTORY = new JacksonFactory();
                final long NUMBER_OF_VIDEOS_RETURNED = 5;

                YouTube youtube = new YouTube.Builder(HTTP_TRANSPORT, JSON_FACTORY, new HttpRequestInitializer() {
                    public void initialize(HttpRequest request) throws IOException {
                    }
                }).setApplicationName("youtube-search-sample").build();

                YouTube.Search.List search = youtube.search().list("id,snippet");

                search.setKey(API_KEY);

                search.setQ("아이린");
                search.setChannelId("UCk9GmdlDTBfgGRb7vXeRMoQ"); //레드벨벳 공식 유투브 채널
                search.setOrder("relevance"); //date relevance

                search.setType("video");

                search.setFields("items(id/kind,id/videoId,snippet/title,snippet/thumbnails/default/url)");
                search.setMaxResults(NUMBER_OF_VIDEOS_RETURNED);
                SearchListResponse searchResponse = search.execute();

                List<SearchResult> searchResultList = searchResponse.getItems();

                if (searchResultList != null) {
                    prettyPrint(searchResultList.iterator(), "레드벨벳");
                }
            } catch (GoogleJsonResponseException e) {
                System.err.println("There was a service error: " + e.getDetails().getCode() + " : "
                        + e.getDetails().getMessage());
                System.err.println("There was a service error 2: " + e.getLocalizedMessage() + " , " + e.toString());
            } catch (IOException e) {
                System.err.println("There was an IO error: " + e.getCause() + " : " + e.getMessage());
            } catch (Throwable t) {
                t.printStackTrace();
            }

            return null;
        }

        @Override
        protected void onPostExecute(Void aVoid) {
            super.onPostExecute(aVoid);
        }

        public void prettyPrint(Iterator<SearchResult> iteratorSearchResults, String query) {
            if (!iteratorSearchResults.hasNext()) {
                System.out.println(" There aren't any results for your query.");
            }

            StringBuilder sb = new StringBuilder();

            while (iteratorSearchResults.hasNext()) {
                SearchResult singleVideo = iteratorSearchResults.next();
                ResourceId rId = singleVideo.getId();

                // Double checks the kind is video.
                if (rId.getKind().equals("youtube#video")) {
                    Thumbnail thumbnail = (Thumbnail) singleVideo.getSnippet().getThumbnails().get("default");
                    sb.append("ID : " + rId.getVideoId() + " , 제목 : " + singleVideo.getSnippet().getTitle() + " , 썸네일 주소 : " + thumbnail.getUrl());
                    sb.append("\n");
                }
            }

            result = sb.toString();
        }
    }
}