Accessing data at different levels in a chain of InputStream types

Question

Hi, I have a requirement to see both the pre- and post- filtered/processed InputStream data read through a chain of input streams. I?m assuming this is a fairly common requirement, and I have come up with a solution that works, but wanted to see if anyone had a better idea ? I?m pretty sure I?m violating some InputStream usage conventions or something here.
Basically, I am using AudioInputStream in AudioSystem to read and decode (so that I can play) an encoded (MP3) audio file. This requires two AudioInputStreams, one to access the encoded source and one to read the decoded audio data:
AudioInputStream encodedAIS = AudioSystem.getAudioInputStream(url);
// set up target audio format (standard AudioFormat.Encoding.PCM_SIGNED for playback using a standard SourceDataLine)
AudioInputStream decodedAIS = AudioSystem.getAudioInputStream(targetAudioFormat, encodedAIS);With this, I can read and then play as follows:
// set up SourceDataLine
decodedAIS.read(?); // read
standardSDL.write(?); // playWhat I?ve done to access the original encoded data is insert a subclass of FilterInputStream in between the encoded and decoded AudioInputStreams. This subclass overrides the read methods to ?retain? a copy of the data most recently read:
private class FilterToRetainInputStream extends FilterInputStream {
     private class RetainedData {
          private byte[] bytes = null;
          private int offset = -1;
          private int length = -1;
          private RetainedData(byte[] b, int off, int len) {
               bytes = new byte[b.length];
               System.arraycopy(b, off, bytes, off, len);
               offset = off;
               length = len;
     private RetainedData retainedData;
     private FilterToRetainInputStream(AudioInputStream ais) {
          super((InputStream)ais);
     @Override
     public int read(byte[] b, int off, int len) throws IOException {
          int ret = super.read(b, off, len);
          retainedData = new RetainedData(b,off,len);
          return ret;
}; I then attach this filter to the original source AudioInputStream and attach a second source AudioInputStream to the filter/retainer:
// the original (encoded) source AudioInputStream
AudioInputStream firstEncodedAIS = AudioSystem.getAudioInputStream(url);
// chain new FilterToRetainInputStream to the source AudioInputStream
FilterToRetainInputStream retainer = new FilterToRetainInputStream(firstEncodedAIS);
// chain a second source AudioInputStream to the new FilterToRetainInputStream
AudioInputStream secondEncodedAIS = new AudioInputStream(retainer,firstEncodedAIS.getFormat(),firstEncodedAIS.getFrameLength());
// and finally, as before get a playable (decoded) AudioInputStream given a target format and a source (encoded) AudioInputStream
AudioInputStream decodedAIS = AudioSystem.getAudioInputStream(targetAudioFormat, secondEncodedAIS);Now, I can access the original (encoded) data when reading from the decoded AudioInputStream:
byte[] abData = new byte[16000];
int nBytesRead = decodedAIS.read(abData, 0, abData.length);
FilterToRetainInputStream.RetainedData encodedData = retainer.retainedData;I don?t really like this solution for a couple of reasons - I?m using a filter that doesn?t really ?filter? anything, I need a second AudioInputStream to attach to the filter and I?m passing an audio input stream through a filter (which is not an audio input stream). Any ideas or suggestions would be appreciated or is it okay to do what I?m doing ? thanks.

Answer 1

For quick assistance post testable script.
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