Reading file chunk by chunk

问题:

I want to read a file piece by piece. The file is split up into several pieces which are stored on different types of media. What I currently do is call each seperate piece of the file and then merge it back to the original file.

The issue is that I need to wait until all the chunks arrive before I can play/open the file. Is it possible to read the chunks as they are arriving as opposed to waiting for them to all arrive.

I am working on media file (movie file).

回答1:

what you want is source data line. This is perfect for when your data is too large to hold it in memory at once, so you can start playing it before you receive the entire file. Or if the file never ends.

look at the tutorial for source data line here

http://docs.oracle.com/javase/6/docs/api/java/io/FileInputStream.html#read

I would use this FileInputSteam

回答2:

See InputSteram.read(byte[]) for reading bytes at a time.

Example code:

try {
    File file = new File("myFile");
    FileInputStream is = new FileInputStream(file);
    byte[] chunk = new byte[1024];
    int chunkLen = 0;
    while ((chunkLen = is.read(chunk)) != -1) {
        // your code..
    }
} catch (FileNotFoundException fnfE) {
    // file not found, handle case
} catch (IOException ioE) {
    // problem reading, handle case
}

回答3:

Instead of older io you can try nio for reading file chunk by chunk in memory not full file (as suggested in above answers). You can use Channel to get datas from multiple source

RandomAccessFile aFile = new RandomAccessFile(
                        "test.txt","r");
        FileChannel inChannel = aFile.getChannel();
        long fileSize = inChannel.size();
        ByteBuffer buffer = ByteBuffer.allocate((int) fileSize);
        inChannel.read(buffer);
        //buffer.rewind();
        buffer.flip();
        for (int i = 0; i < fileSize; i++)
        {
            System.out.print((char) buffer.get());
        }
        inChannel.close();
        aFile.close();