Download file via HTTP with unknown length with Java

Question

I want to download a HTTP query with java, but the file I download has an undetermined length when downloading.

I thought this would be quite standard, so I searched and

Answer 1

This should work, i tested it and it works for me:

void downloadFromUrl(URL url, String localFilename) throws IOException {
    InputStream is = null;
    FileOutputStream fos = null;

    try {
        URLConnection urlConn = url.openConnection();//connect

        is = urlConn.getInputStream();               //get connection inputstream
        fos = new FileOutputStream(localFilename);   //open outputstream to local file

        byte[] buffer = new byte[4096];              //declare 4KB buffer
        int len;

        //while we have availble data, continue downloading and storing to local file
        while ((len = is.read(buffer)) > 0) {  
            fos.write(buffer, 0, len);
        }
    } finally {
        try {
            if (is != null) {
                is.close();
            }
        } finally {
            if (fos != null) {
                fos.close();
            }
        }
    }
}

If you want this to run in background, simply call it in a Thread:

Thread download = new Thread(){
    public void run(){
        URL url= new URL("http://overpass-api.de/api/interpreter?data=area%5Bname%3D%22Hoogstade%22%5D%3B%0A%28%0A++node%28area%29%3B%0A++%3C%3B%0A%29+%3B%0Aout+meta+qt%3B");
        String localFilename="mylocalfile"; //needs to be replaced with local file path
        downloadFromUrl(url, localFilename);
    }
};
download.start();//start the thread