Downloading files using Java randomly freezes
io, java
Solution
The problem you are facing is caused by Java 7 - in detail that to gives IPv6 a higher priority than IPv4.
You can change it back to IPv4 as it was used in Java 6 by setting the system property `System.setProperty("java.net.preferIPv4Stack", "true");`
This problem affects all Java based software but only occurs on some computers (may depend on the internet connection used): Downloads stops - “TCP Window Full”
Problem
When I try to download a file (in this case it's just an image but the real application is an updating mechanism), the `InputStream` seems to freeze on `read`. I'm pretty sure my code is okay, so I'm wondering why this happens and if it's just on my computer. Could someone please run this? Please note that the `Timer` is simply for debugging purposes. Thank you kindly. Here is a video showing the problem: Video ``` import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.io.*; import java.net.URL; import javax.swing.Timer; public class FileDownloader { public final static int BUFFER_LENGTH = 1 << 14; private static Timer timeoutTimer = new Timer(5000, new ActionListener(){ @Override public void actionPerformed(ActionEvent e) { System.out.println("Timeout"); System.exit(0); } }); public static void main(String [] args) throws Exception{ URL url = new URL("http://host.trivialbeing.org/up/tdk-aug3-jokr-high-res-2.jpg"); download(url, new File("joker.jpg")); } public static void download(final URL url, final File dest) throws IOException { FileOutputStream fos = new FileOutputStream(dest); BufferedOutputStream out = new BufferedOutputStream(fos); BufferedInputStream in = new BufferedInputStream(url.openStream()); byte[] buf = new byte[BUFFER_LENGTH]; int bytesRead; int bytesWritten = 0; timeoutTimer.start(); while ((bytesRead = in.read(buf, 0, BUFFER_LENGTH)) != -1) { timeoutTimer.restart(); out.write(buf, 0, bytesRead); out.flush(); bytesWritten += bytesRead; System.out.println(bytesWritten / 1024 + " kb written"); } in.close(); out.close(); System.out.println("Finished"); fos.close(); } } ```