如何从链接逐行读取文本并设置为字符串

Question

我想从此链接（http://jigsaweb.somee.com/Web/text.txt）逐行读取文本文件，并将每一行设置为一个String。之后，从每个字符串读取链接，然后连续播放视频。当我手动编写指向字符串的链接时，它终于可以工作了。但是，当我想从文本文件中读取链接时，我的应用程序会停止运行。在日志中显示“ java.lang.NullPointerException”。请帮我。我的代码有什么问题？

public class MainActivity extends AppCompatActivity {

VideoView videoView;
int i = 0;
int k = 1;

String path;
String link;
String link1;
String link2;
String link3;


List<String> videoPathes = new ArrayList<String>();



@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    this.requestWindowFeature(Window.FEATURE_NO_TITLE);
    this.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);

    getWindow().getDecorView().setSystemUiVisibility(View.SYSTEM_UI_FLAG_HIDE_NAVIGATION);
    setContentView(R.layout.activity_main);


    ActivityCompat.requestPermissions(MainActivity.this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, 1);
    ActivityCompat.requestPermissions(MainActivity.this, new String[]{Manifest.permission.READ_EXTERNAL_STORAGE}, 1);


    videoView = (VideoView) findViewById(R.id.videoView);

    try {
        URL url = new URL("http://jigsaweb.somee.com/Web/text.txt");

        BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));
        String str = in.readLine();
        while (str != null) {
            switch (k) {
                case 1:
                    link = str;
                    break;
                case 2:
                    link1 = str;
                    break;
                case 3:
                    link2 = str;
                    break;
                case 4:
                    link3 = str;
                    break;
                default:
                    link = null;
                    break;
            }
            k++;
        }
        in.close();
    } catch (MalformedURLException e) {
    } catch (IOException e) {
    }catch (NetworkOnMainThreadException e){

    }



        try {
            FileCache cache = new FileCache(new File(getExternalCacheDir(), "cachename"));
            HttpUrlSource source = new HttpUrlSource(link);
            HttpProxyCache proxyCache = new HttpProxyCache(source, cache);
            videoPathes.add(proxyCache.getUrl());

            FileCache cache1 = new FileCache(new File(getExternalCacheDir(), "cachename1"));
            HttpUrlSource source1 = new HttpUrlSource(link1);
            HttpProxyCache proxyCache1 = new HttpProxyCache(source1, cache1);
            videoPathes.add(proxyCache1.getUrl());

            FileCache cache2 = new FileCache(new File(getExternalCacheDir(), "cachename2"));
            HttpUrlSource source2 = new HttpUrlSource(link2);
            HttpProxyCache proxyCache2 = new HttpProxyCache(source2, cache2);
            videoPathes.add(proxyCache2.getUrl());

            FileCache cache3 = new FileCache(new File(getExternalCacheDir(), "cachename3"));
            HttpUrlSource source3 = new HttpUrlSource(link3);
            HttpProxyCache proxyCache3 = new HttpProxyCache(source3, cache3);
            videoPathes.add(proxyCache3.getUrl());
        } catch (ProxyCacheException e) {
            Log.e("Tag1", "Error playing video", e);
        }


        path = "https://view.vzaar.com/15313699/video";

        final Uri uri = Uri.parse(link);
        videoView.setVideoPath(videoPathes.get(0));
        videoView.requestFocus();
        videoView.start();

        videoView.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {
            public void onCompletion(final MediaPlayer mp) {
                i = (i + 1) % videoPathes.size();
                Log.d("tag0", i + "");
                videoView.setVideoURI(Uri.parse(videoPathes.get(i)));
                videoView.requestFocus();
                videoView.start();
            }

        });

}

@Override
public void onWindowFocusChanged(boolean hasFocus) {
    super.onWindowFocusChanged(hasFocus);
    if (hasFocus) {
        getWindow().getDecorView().setSystemUiVisibility(
                View.SYSTEM_UI_FLAG_LAYOUT_STABLE
                        | View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION
                        | View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN
                        | View.SYSTEM_UI_FLAG_HIDE_NAVIGATION
                        | View.SYSTEM_UI_FLAG_FULLSCREEN
                        | View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY);
    }
}
}

这是崩溃：

2019-01-13 16:08:59.870 7273-7273/com.karhakobyan.adplayer E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.karhakobyan.adplayer, PID: 7273
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.karhakobyan.adplayer/com.karhakobyan.adplayer.MainActivity}: java.lang.NullPointerException
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2778)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856)
    at android.app.ActivityThread.-wrap11(Unknown Source:0)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589)
    at android.os.Handler.dispatchMessage(Handler.java:106)
    at android.os.Looper.loop(Looper.java:164)
    at android.app.ActivityThread.main(ActivityThread.java:6494)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
 Caused by: java.lang.NullPointerException
    at com.danikula.videocache.Preconditions.checkNotNull(Preconditions.java:7)
    at com.danikula.videocache.HttpUrlSource.<init>(HttpUrlSource.java:33)
    at com.danikula.videocache.HttpUrlSource.<init>(HttpUrlSource.java:29)
    at com.karhakobyan.adplayer.MainActivity.onCreate(MainActivity.java:108)
    at android.app.Activity.performCreate(Activity.java:7009)
    at android.app.Activity.performCreate(Activity.java:7000)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1214)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2731)