要在Android應用中使用USB攝像頭，首先需要確保設備支持USB攝像頭，并且已經連接到設備上。接下來，可以按照以下步驟在應用中使用USB攝像頭：

1. 在AndroidManifest.xml文件中添加以下權限：

<uses-feature android:name="android.hardware.usb.host" />
<uses-permission android:name="android.permission.CAMERA" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />

2. 需要使用USB權限，可以在應用的Activity中請求USB權限：

private static final String ACTION_USB_PERMISSION = "com.android.example.USB_PERMISSION";

private final BroadcastReceiver usbReceiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
        String action = intent.getAction();
        if (ACTION_USB_PERMISSION.equals(action)) {
            synchronized (this) {
                UsbDevice device = intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);
                if (intent.getBooleanExtra(UsbManager.EXTRA_PERMISSION_GRANTED, false)) {
                    if (device != null) {
                        // 打開USB攝像頭
                        // 獲取USB設備的ID和攝像頭信息
                    }
                } else {
                    Log.d(TAG, "permission denied for device " + device);
                }
            }
        }
    }
};

private void requestUSBPermission() {
    UsbManager usbManager = (UsbManager) getSystemService(Context.USB_SERVICE);
    UsbDevice device = ... // 獲取USB設備
    PendingIntent permissionIntent = PendingIntent.getBroadcast(this, 0, new Intent(ACTION_USB_PERMISSION), 0);
    IntentFilter filter = new IntentFilter(ACTION_USB_PERMISSION);
    registerReceiver(usbReceiver, filter);
    usbManager.requestPermission(device, permissionIntent);
}

3. 初始化USB攝像頭，并啟動預覽：

private Camera camera;
private SurfaceView surfaceView;
private SurfaceHolder surfaceHolder;

@Override
public void surfaceCreated(SurfaceHolder holder) {
    try {
        camera = Camera.open();
        camera.setPreviewDisplay(holder);
        camera.startPreview();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

@Override
protected void onResume() {
    super.onResume();
    if (surfaceHolder != null) {
        surfaceCreated(surfaceHolder);
    }
}

@Override
protected void onPause() {
    super.onPause();
    if (camera != null) {
        camera.stopPreview();
        camera.release();
        camera = null;
    }
}

通過以上步驟，就可以在Android應用中成功使用USB攝像頭。需要注意的是，使用USB攝像頭可能會因為不同設備和Android版本的差異而有所不同，需要根據具體情況進行調整。