waffel’s Weblog

Oktober 9, 2007

Fast stream copy using java.nio channels

Filed under: java,nio,software — Thomas Wabner @ 11:21 am
Tags: , , ,

Many times I was asked how to copy fast and simple an input stream to an output stream. I have found a nice solution on koders.com . A programmer named Mr. Hitchens has contributed this code.

Here are my utility method which makes the real fast copy stuff:

public final class ChannelTools {
  public static void fastChannelCopy(final ReadableByteChannel src, final WritableByteChannel dest) throws IOException {
    final ByteBuffer buffer = ByteBuffer.allocateDirect(16 * 1024);
    while (src.read(buffer) != -1) {
      // prepare the buffer to be drained
      // write to the channel, may block
      // If partial transfer, shift remainder down
      // If buffer is empty, same as doing clear()
    // EOF will leave buffer in fill state
    // make sure the buffer is fully drained.
    while (buffer.hasRemaining()) {

And how you can use this method to copy an input stream into an output stream? Here comes the answer:

// allocate the stream ... only for example
final InputStream input = new FileInputStream(inputFile);
final OutputStream output = new FileOutputStream(outputFile);
// get an channel from the stream
final ReadableByteChannel inputChannel = Channels.newChannel(input);
final WriteableByteChannel outputChannel = Channels.newChannel(output);
// copy the channels
ChannelTools.fastChannelCopy(inputChannel, outputChannel);
// closing the channels


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