使用Android Webview下载文件

Question

I am making an Android app that uses a WebView to access to a webpage. To handle downloads I am using AsyncTask in method onDownloadStart of WebView's DownloadListener. However files downloaded are blank (although the filename and extension are correct). My Java code is this:

protected String doInBackground(String... url) {  
    try {
        URL url = new URL(url[0]);    

        //Creating directory if not exists

        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        connection.setRequestMethod("GET");
        connection.setDoOutput(true);        
        connection.connect();

        //Obtaining filename

        File outputFile = new File(directory, filename);
        InputStream input   = new BufferedInputStream(connection.getInputStream());
        OutputStream output = new FileOutputStream(outputFile);

        byte data[] = new byte[1024];
        int count = 0;
        Log.e(null, "input.read(data) = "+input.read(data), null);
        while ((count = input.read(data)) != -1) {
            output.write(data, 0, count);
        }              
        connection.disconnect();
        output.flush();
        output.close();
        input.close();
    } catch (MalformedURLException e) {
        e.printStackTrace();
    } catch (IOException e) {
         e.printStackTrace();
    }
    return null;
}

log.e line gives -1 value for input.read(data). PHP code of download page is this (works in all platforms). Files are stored in non-public directories of my HTML server.

<?php
$guid = $_GET['id'];
$file = get_file($guid);

if (isset($file['path'])) { 
    $mime = $file['MIMEType'];
    if (!$mime) {
        $mime = "application/octet-stream";
    }

    header("Pragma: public");
    header("Content-type: $mime");
    header("Content-Disposition: attachment; filename=\"{$file['filename']}\"");
    header('Content-Transfer-Encoding: binary');

    ob_clean();
    flush();
    readfile($file['path']);
    exit();

}
?>

I've noticed that if I write some text after "?>" of PHP file, this text is written in the file downloaded.

Answer 1

In your code, you are using ob_clean() , which will just erase the output buffer. Your subsequent call to flush() therefore doesn't return anything, because the output buffer has been flushed beforehand.

Instead of ob_clean() and flush() , use ob_end_flush() . This will stop output buffering and it will send all the output it withheld.

ob_end_flush — Flush (send) the output buffer and turn off output buffering

If you want to stop output buffering without outputting whatever is saved, you can use ob_end_clean() . Anything after this command will be output again, but anything between ob_start() and ob_end_clean() will be "swallowed."

ob_end_clean — Clean (erase) the output buffer and turn off output buffering

What are the benefits of output buffering in the first place? If you are doing ob_start() and then using flush() on everything you might as well output everything directly.