在有效的url字符串上获取“java.net.malformedurexception:no protocol”异常?

我正在尝试用kotlin编写一个android应用程序,通过web下载mp3文件。出现问题的代码如下:

fun downloadAudio(url: String, f: File) {
    Log.d(JOURNAL_FETCHR_TAG, "URL is $url")
    val iStream: InputStream = URL(url).openStream() // EXCEPTION ON THIS LINE
    val oStream: OutputStream = FileOutputStream(f)
    var buffer = ByteArray(1024)
    var len = iStream.read(buffer)

    while (len > 0) {
        oStream.write(buffer, 0, len)
        len = iStream.read(buffer)
    }
    oStream.close()
}

E/AndroidRuntime: FATAL EXCEPTION: IntentService[DownloadIntentService]
                  Process: com.sarpuner.journal, PID: 23301
                  java.net.MalformedURLException: no protocol: "http://telechargement.rfi.fr/rfi/francais/audio/jff/201808/journal_francais_facile_20h00_-_20h10_tu_20180819.mp3"
                      at java.net.URL.<init>(URL.java:601)
                      at java.net.URL.<init>(URL.java:498)
                      at java.net.URL.<init>(URL.java:447)
                      at com.sarpuner.journal.JournalFetchrKt.downloadAudio(JournalFetchr.kt:78)
                      at com.sarpuner.journal.DownloadIntentService.onHandleIntent(DownloadIntentService.kt:24)
                      at android.app.IntentService$ServiceHandler.handleMessage(IntentService.java:76)
                      at android.os.Handler.dispatchMessage(Handler.java:106)
                      at android.os.Looper.loop(Looper.java:193)
                      at android.os.HandlerThread.run(HandlerThread.java:65)

不过,这个url看起来不错,所以我无法找出错误的原因。感谢您的帮助。