如何获得使用AudioInputStream Java下载文件的进度

Question

I am new to downloading a file with java and sorry if its a dumb question but I've searched for 2 days and couldn't get a solution. I am using JPanel within an applet and I want to show the download progress in a progressBar.(maybe download is not the correct word it is more likely an initialization)

What i want is to show a download process of a wav file from an URL.I don't mean to show the reading process(i will let the user know the file is being processed later.) i just want to get the progress of ais=AudioSystem.getAudioInputStream(url);

i tried to use ProgressMonitorInputStream but this doesn't work for me, because i want to add the progress bar to my JFrame. I have looked for swingWorker but the usage of it does not give me the progress i want.

Here is my read function. I am also changing the wav format according to my needs.

    public void readFile() {

    byte[] data = null;
    AudioInputStream ais = null;
    try {
        URL url = new URL("http://www-mmsp.ece.mcgill.ca/documents/AudioFormats/WAVE/Samples/AFsp/M1F1-Alaw-AFsp.wav");
        ais = AudioSystem.getAudioInputStream(url);


        AudioFormat format = ais.getFormat();
        numberOfChannels = format.getChannels();



        AudioFormat TargetFormat = new AudioFormat(format.getSampleRate(), 16, numberOfChannels, true, false);
        AudioInputStream desiredFormatStream = AudioSystem.getAudioInputStream(TargetFormat,ais);
        data = new byte[4];
        int totalSampleCount = ais.available()/(format.getSampleSizeInBits()/8);


        audio = new double[totalSampleCount];
        for (int i = 0; i < totalSampleCount-1; i=i+2) {
            desiredFormatStream.read(data);

                if(!TargetFormat.isBigEndian()){
                    audio[i] = ((short) (((data[1] & 0xFF) << 8) + (data[0] & 0xFF))) / ((double) MAX_16_BIT);
                    audio[i+1] = ((short) (((data[3] & 0xFF) << 8) + (data[2] & 0xFF))) / ((double) MAX_16_BIT);
                }
                else {
                    audio[i] = ((short) (((data[0] & 0xFF) << 8) + (data[1] & 0xFF))) / ((double) MAX_16_BIT);
                    audio[i+1] = ((short) (((data[2] & 0xFF) << 8) + (data[3] & 0xFF))) / ((double) MAX_16_BIT);
                }

        }

        StdAudio.open(TargetFormat);

    } catch (Exception e) {
        System.out.println(e.getMessage());
        throw new RuntimeException("Could not read " + filename);
    }
}

Is there any way to achieve this?

Thanks in advance.

Answer 1

The easiest way is to open a URLConnection on your already present URL -object and query the Content-Length http-header field. Use the getContentLength() -method to do so.

NOTE if you're downloading large files, an int might not be big enough to hold the content length. Therefor, getContentLengthLong() should be prefered. This method is available since Java 7 .

This will hold the length of the file in bytes. When you're reading via AudioInputStream.read() , this method will return the actual amount of bytes read each time.

Pseudo-code

long totalLength = con.getContentLengthLong();
while still reading{
  long totalBytesRead += in.read();
  print "Process: "+(totalBytesRead * 100 / totalLength);
}

See also :

• Similar question with examples on using the content-length
• Article on using unbuffered streams