Downloading a portion of a File using HTTP Requests

Question

I am trying to download a portion of a PDF file (just for testing "Range" header). I requested the server for the bytes (0-24) in Range but still, instead of getting first 25 bytes (a portion) out of the content, I am getting the full length content. Moreover, instead of getting response code as 206 (partial content), I'm getting response code as 200.

Here's my code:

public static void main(String a[]) {
    try {
        URL url = new URL("http://download.oracle.com/otn-pub/java/jdk/7u21-b11/jdk-7u21-windows-x64.exe?AuthParam=1372502269_599691fc0025a1f2da7723b644f44ece");
        HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
        urlConnection.setRequestProperty("Range", "Bytes=0-24");
        urlConnection.connect();

        System.out.println("Respnse Code: " + urlConnection.getResponseCode());
        System.out.println("Content-Length: " + urlConnection.getContentLengthLong());

        InputStream inputStream = urlConnection.getInputStream();
        long size = 0;

        while(inputStream.read() != -1 )
            size++;

        System.out.println("Downloaded Size: " + size);

    }catch(MalformedURLException mue) {
        mue.printStackTrace();
    }catch(IOException ioe) {
        ioe.printStackTrace();
    }
}

Here's the output:
Respnse Code: 200
Content-Length: 94973848
Downloaded Size: 94973848

Thanks in Advance.

Polymorphism

Can you verify that a program that can download ranges does indeed download a range? (try starting wget, Ctrl+C'ing it, and starting it again) Some servers may reject the request as-is. – Harmonist

Answer 1

Try changing following:

urlConnection.setRequestProperty("Range", "Bytes=0-24");

with:

urlConnection.setRequestProperty("Range", "bytes=0-24");

as per the spec 14.35.1 Byte Ranges

Similarly, as per the spec 14.5 Accept-Ranges, you can also check whether your server actually supports partial content retrieval or not using following:

boolean support = urlConnection.getHeaderField("Accept-Ranges").equals("bytes");
System.out.println("Partial content retrieval support = " + (support ? "Yes" : "No));

Laplace

Some servers unforutnately may properly respond with 206 but not have Accept-Ranges header at all. – Guyenne

Answer 2

If the server supports it (and HTTP 1.1 servers should), only then you can use range requests... and if all you want to do is check, then just send a HEAD request instead of a GET request. Same headers, same everything, just "HEAD" instead of "GET". If you receive a 206 response, you'll know Range is supported, and otherwise you'll get a 200 response.

Unnumbered

gstack, I sent a "HEAD" request and got response code as 200. This must imply that the server does not support "Resuming" downloads feature. Then, I would like to know, how am I able to "pause" and "resume" this file's download in other download managers. Also, it would be great if you could suggest any http links whose content-portion can be downloaded by this method. – Polymorphism

Answer 3

You have to connect to url before setRequestProperty

Change:

urlConnection.setRequestProperty("Range", "Bytes=0-24");
urlConnection.connect();

To:

urlConnection.connect();
urlConnection.setRequestProperty("Range", "Bytes=0-24");

Crummy

Answer 4

I think the correct header is "Content-Range", not "Range" as you are using.

Unnumbered

gstack, tried it with "Content-Range" too; getting the same output – Polymorphism

Nope AFAIK. content-range is what the server responses. Range what you have to request. – Wensleydale