我的Java代码下载了一个文件，但是大小错误

Question

The following code creates a file, but it is not openable, and the file size it creates does not remotely correspond with the size of the file I am trying to download. (using whatsapp updater link as an example):

 private static boolean download(){
        try {
            String outfile = "/sdcard/whatsapp.apk";
            URL download = new URL("https://www.whatsapp.com/android/current/WhatsApp.apk");
            ReadableByteChannel rbc = Channels.newChannel(download.openStream());
            FileOutputStream fileOut = new FileOutputStream(outfile);
            fileOut.getChannel().transferFrom(rbc, 0, 1 << 24);
            fileOut.close();
            rbc.close();
            return true;
        } catch (IOException ioe){
            return false;
        }
    }

EDIT: this is a shortened version of my full code, (the full code alows network ops on main thread, and trust all certificates), also changed the code in the question.

Tests show that IOException is not being throw, and code completes without error. so, Why is the downloaded file not usable?

Answer 1

From the Javadoc :

Fewer than the requested number of bytes will be transferred if the source channel has fewer than count bytes remaining, or if the source channel is non-blocking and has fewer than count bytes immediately available in its input buffer.

This means that it is not guaranteed that this will save the entire file at once. You should put this call in a loop which breaks once the entire download has completed.