Question

I try to download a zip file to android and then extract the zip file. I debug my code and there is a funny problem: The downloaded zip file is a bit larger than origin file. And the downloaded zip file can’t be unziped by winrar. It is said that the downloaded file is ended with error. (The zip file on my website is OK. I try to download with IE. It works fine.)
Following is my code:

public void download(final String url, final String savePath, final String saveName) {
    new Thread(new Runnable() {
        public void run() {
            try {
                sendMessage(FILE_DOWNLOAD_CONNECT);
                URL sourceUrl = new URL(url);
                URLConnection conn = sourceUrl.openConnection();
                conn.connect();
                InputStream inputStream = conn.getInputStream();

                int fileSize = conn.getContentLength();

                File savefilepath = new File(savePath);
                if (!savefilepath.exists()) {
                    savefilepath.mkdirs();
                }
                File savefile = new File(savePath+saveName);
                if (savefile.exists()) {
                    savefile.delete();
                }
                savefile.createNewFile();

                FileOutputStream outputStream = new FileOutputStream(
                    savePath+saveName, true);

                byte[] buffer = new byte[1024];
                int readCount = 0;
                int readNum = 0;
                int prevPercent = 0;
                while (readCount < fileSize && readNum != -1) {
                    readNum = inputStream.read(buffer);
                    if (readNum > -1) {
                        outputStream.write(buffer);

                        readCount = readCount + readNum;

                        int percent = (int) (readCount * 100 / fileSize);
                        if (percent > prevPercent) {
                            sendMessage(FILE_DOWNLOAD_UPDATE, percent,
                                readCount);

                            prevPercent = percent;
                        }
                    }
                }
                outputStream.flush();
                outputStream.close();
                inputStream.close();
                //Thread.sleep(50);
                sendMessage(FILE_DOWNLOAD_COMPLETE, savePath);

            } catch (Exception e) {
                sendMessage(FILE_DOWNLOAD_ERROR, e);
            }
        }
    }).start();
}

Anybody know this issue?

Answer 1

When you read into the buffer, you are writing the entire buffer to the output stream:

outputStream.write(buffer);

You should only write the part of the buffer that was filled:

outputStream.write(buffer, 0, readNum);

Particularly with network downloads, there is no guarantee that a call to inputStream.read(buffer) will fill the buffer (even if there is more than 1024 bytes to go in the file).