WebClient.DownloadString(url) does not work with 2nd parameter

Question

I am using the WebClient.DownloadString() method to download some data. I am using the following code:

static void Main(string[] args)
    {
        string query = "select+%3farticle+%3fmesh+where+{+%3farticle+a+npg%3aArticle+.+%3farticle+npg%3ahasRecord+[+dc%3asubject+%3fmesh+]+.+filter+regex%28%3fmesh%2c+\"blood\"%2c+\"i\"%29+}";
        NameValueCollection queries = new NameValueCollection();
        queries.Add("query", query);
        //queries.Add("output", "sparql_json");
        using (WebClient wc = new WebClient())
        {
            wc.Headers.Add("user-agent", "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; .NET CLR 1.0.3705;)");
            wc.QueryString = queries;
            string result = wc.DownloadString("http://data.nature.com/sparql");
            Console.WriteLine(result);
        }
        Console.ReadLine();
    }

With this code, tt works fine and gives me an xml string as the output. But I would like to get a JSON output and hence I un-commented the line

queries.Add("output", "sparql_json");

and executed the same program and it seems to be fetching an error message from the server.

However, if I try to use a web browser and use the same url (as given below), it gives me a JSON as expected: URL that works in browsers

I am wondering what the problem could be. Especially when it works in a browser and not using a webclient. Is the webclient doing something different here?

Please note that I also tried to specify the query as

query + "&output=sparql_json"

But that does not work either.

Could someone please tell me what the problem might be?

Thanks

in your string query = "..." initialization, should you be encoding the value already? I don't think you should be. Put it as plain-text and let queries.Add("query", query) encode it for you. — Matthew
– Matthew, Commented Apr 5, 2012 at 17:08
Matthew, the problem is not with the query. With just the query, it works fine - it gives me an xml. But if i try to do an "&output=sparql_json" along with the query, i get an error. Any ideas? — Ram
– Ram, Commented Apr 5, 2012 at 17:11
It could be the browser fixing up a faulty query string for you automatically, pretty sure it's your query string that needs fixing. — Matthew
– Matthew, Commented Apr 5, 2012 at 17:17
Matthew, Thanks a lot for the comments. Apparently, as L.B suggested, I just had to include the Accept Json header and changing nothing else. The query string (encoded or not) gives me just the same result. — Ram
– Ram, Commented Apr 5, 2012 at 17:23

L.B · Accepted Answer · 2012-04-05 17:15:16Z

6

Add wc.Headers.Add("Accept","application/json");. Here is the full source I tested

string query = "select ?article ?mesh where { ?article a npg:Article . ?article npg:hasRecord [ dc:subject ?mesh ] . filter regex(?mesh, \"blood\", \"i\") }";
NameValueCollection queries = new NameValueCollection();
queries.Add("query", query);
queries.Add("output", "sparql_json");
using (WebClient wc = new WebClient())
{
    wc.Headers.Add("user-agent", "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; .NET CLR 1.0.3705;)");
    wc.Headers.Add("Accept","application/json");
    wc.QueryString = queries;
    string result = wc.DownloadString("http://data.nature.com/sparql");
    Console.WriteLine(result);
}
Console.ReadLine();

answered Apr 5, 2012 at 17:15

L.B

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2 Comments

Ram Over a year ago

Thats amazing. I have downloaded a json before but I never specified the Headers.Add("Accept","application/json"); Does it have anything to do with the server? Anyways, the solution worked. Thanks a lot!!

Ram Over a year ago

To add to my previous comment, the solution was to add the extra header that you suggested : wc.Headers.Add("Accept","application/json"); made all the difference. Thanks!

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