Easy way to write contents of a Java InputStream to an OutputStream

Question

I was surprised to find today that I couldn\'t track down any simple way to write the contents of an InputStream to an OutputStream in Java. Obviou

Answer 1

Here comes how I'm doing with simplest for loop.

private void copy(final InputStream in, final OutputStream out)
    throws IOException {
    final byte[] b = new byte[8192];
    for (int r; (r = in.read(b)) != -1;) {
        out.write(b, 0, r);
    }
}

Answer 2

Another possible candidate are the Guava I/O utilities:

http://code.google.com/p/guava-libraries/wiki/IOExplained

I thought I'd use these since Guava is already immensely useful in my project, rather than adding yet another library for one function.

Answer 3

Using Guava's ByteStreams.copy():

ByteStreams.copy(inputStream, outputStream);

Answer 4

For those who use Spring framework there is a useful StreamUtils class:

StreamUtils.copy(in, out);

The above does not close the streams. If you want the streams closed after the copy, use FileCopyUtils class instead:

FileCopyUtils.copy(in, out);

Answer 5

Using Java7 and try-with-resources, comes with a simplified and readable version.

try(InputStream inputStream = new FileInputStream("C:\\mov.mp4");
    OutputStream outputStream = new FileOutputStream("D:\\mov.mp4")) {

    byte[] buffer = new byte[10*1024];

    for (int length; (length = inputStream.read(buffer)) != -1; ) {
        outputStream.write(buffer, 0, length);
    }
} catch (FileNotFoundException exception) {
    exception.printStackTrace();
} catch (IOException ioException) {
    ioException.printStackTrace();
}

Answer 6

I think it's better to use a large buffer, because most of the files are greater than 1024 bytes. Also it's a good practice to check the number of read bytes to be positive.

byte[] buffer = new byte[4096];
int n;
while ((n = in.read(buffer)) > 0) {
    out.write(buffer, 0, n);
}
out.close();