Java NIO。 是否可以模拟基本下载应用程序的有效解决方案？

Question

I'm trying to simulate a simple download application by copying a file like myBook.txt and saving it as newBook.txt within the same Java Package.

I've managed to get it working on my workstation but how would I go about getting it to work on another? The path's that I supply will be different up until the project name eg "SimpleDownloadCentre\\\\..."

private final String SOURCE_PATH = "C:\\Users\\...\\Documents\\NetBeansProjects\\"
            + "SimepleDownloadCentre\\src\\simpledownloadcentre\\"
            + "myBook.txt";

private final String DESTINATION_PATH = "C:\\Users\\...\\Documents\\NetBeansProjects\\"
            + "SimepleDownloadCentre\\src\\simpledownloadcentre\\"
            + "newBook.txt";

public void startDownload() {
        FileInputStream fis = null;
        try {
            String destination = DESTINATION_PATH;
            String source = SOURCE_PATH;

            fis = new FileInputStream(source);
            FileOutputStream fos = new FileOutputStream(destination);

            FileChannel fci = fis.getChannel();
            FileChannel fco = fos.getChannel();

            ByteBuffer buffer = ByteBuffer.allocate(1024);

            while (true) {
                try {
                    int read = fci.read(buffer);
                    if (read == -1) {
                        break;
                    }
                    buffer.flip();

                    fco.write(buffer);

                    buffer.clear();
                } catch (IOException ex) {
                    System.err.println("ERROR: unable to read block");
                }
            }
        } catch (FileNotFoundException ex) {
            System.err.println("ERROR: file not found");
        } finally {
            try {
                fis.close();
            } catch (IOException ex) {
                System.err.println("ERROR: unable to close file channel");
            }
        }
    }

Is Java NIO the wrong approach for the solution I'm after?

Thanks in advance

Answer 1

NIO is not a problem, though it won't help much more than using IO.

What I would do is:

• Use a bigger buffer eg 32 KB.
• Use a direct buffer (its faster than using a heap one in this case)
• Use a Socket connection to simulate a network/download connection.

You can do all this (except the direct buffer) using plain IO of course.

If you don't need the Sockets and just want to transfer data I would use transferTo/transferFrom to perform the copy.

In summary: Using NIO is not a bad or good idea.

Answer 2

Your copy loop is incorrect. It can lose data if write() doesn't write the entire buffer. It should read as follows:

while ((read = in.read(buffer)) >= 0 || buffer.position() > 0)
{
  buffer.flip();
  out.write(buffer);
  buffer.compact();
}