Making PUT request with JSON data using HttpURLConnection is not working

Question

I'm trying to make PUT request with JSON data using HttpURLConnection in Java. The way I do it doesn't work. I get no errors so I don't know what the problem is.

public static void main(String[] args) {

        URL url;
        try {
            url = new URL("http://fltspc.itu.dk/widget/515318fe17450f312b00153d/");
            HttpURLConnection hurl = (HttpURLConnection) url.openConnection();
            hurl.setRequestMethod("PUT");
            hurl.setDoOutput(true);
            hurl.setRequestProperty("Content-Type", "application/json");
            hurl.setRequestProperty("Accept", "application/json");

            String payload = "{'pos':{'left':45,'top':45}}";

            OutputStreamWriter osw = new OutputStreamWriter(hurl.getOutputStream());
            osw.write(payload);
            osw.flush();
            osw.close();
        } catch (MalformedURLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

And here is the request I'm actually trying to make:

I was already making GET requests to the resource within the same app and it worked fine. I would be very grateful for all tips on how can I debug that or how can I try to do it some other way. So far I tried only using OutputStream instead of OutputStreamWriter but it doesn't work neither.

Answer 1

The Sun (Oracle) implementation of HttpURLConnection caches the content of your post unless you tell it to be in streaming mode. The content will be sent if you start interaction with the response such as:

hurl.getResponseCode();

Also, according to RFC 4627 you can not use single quotes in your json (although some implementations seem to not care).

So, change your payload to:

String payload = "{\"pos\":{\"left\":45,\"top\":45}}";

This example works for me

public class HttpPut {
    public static void main(String[] args) throws Exception {
        Random random = new Random();
        URL url = new URL("http://fltspc.itu.dk/widget/515318fe17450f312b00153d/");
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        connection.setRequestMethod("PUT");
        connection.setDoOutput(true);
        connection.setRequestProperty("Content-Type", "application/json");
        connection.setRequestProperty("Accept", "application/json");
        OutputStreamWriter osw = new OutputStreamWriter(connection.getOutputStream());
        osw.write(String.format("{\"pos\":{\"left\":%1$d,\"top\":%2$d}}", random.nextInt(30), random.nextInt(20)));
        osw.flush();
        osw.close();
        System.err.println(connection.getResponseCode());
    }
}