MP3 header reading

Question

Hi.
I am making a simple music player and would like to be able to read the header of the MP3 file. I have searched somewhat on the internet but I have found no solution, yet. I found articles about getting the MP3 file into a byte[] and then read the bits inside each byte. I need a little help on that since I don't know how to (doh :) ). I found this code on the internet:
    private static long length = 0;
// Returns the contents of the file in a byte array.
    public static byte[] getBytesFromFile(File file) throws IOException {
        InputStream is = new FileInputStream(file);
        // Get the size of the file
         length = file.length();
        // You cannot create an array using a long type.
        // It needs to be an int type.
        // Before converting to an int type, check
        // to ensure that file is not larger than Integer.MAX_VALUE.
        if (length > Integer.MAX_VALUE) {
            // File is too large
        // Create the byte array to hold the data
        byte[] bytes = new byte[(int)length];
        // Read in the bytes
        int offset = 0;
        int numRead = 0;
        while (offset < bytes.length
               && (numRead=is.read(bytes, offset, bytes.length-offset)) >= 0) {
            offset += numRead;
        // Ensure all the bytes have been read in
        if (offset < bytes.length) {
            throw new IOException("Could not completely read file "+file.getName());
        // Close the input stream and return bytes
        is.close();
        return bytes;
    }This gives me an byte array of the file but now I need to find the bytes that contain information about the header AND I need to look at each byte individually AND divide them into bits.
Help...
Thanks
Simmi

Answer 1

First think I'd say is that it's pretty pointless reading the whole file, when all you want is the first few dozen bytes. MP3 files tend to be quite large.
I don't know the details of the various formats you'll have to interpret, but you might be best to use a DataInputStream, or you might want to get fancy and use a mapped byte buffer. To do that you open the MP3 as a RandomAccessFile and get the FileChanel. From the FileChanel you can get a mapped ByteBuffer, from which you can read a variety of binary data formats. You can also specify whether multi-byte numbers are little-endian or big-endian.
With the differences in formats it's probably not for the faint-hearted.