HttpURLConnection getInputStream FileNotFoundException

Hello Android/Java coders!

So I recently got some weird errors when doing HTTP requests in my Android game Hamster Climb. I was trying to get the input stream from a HttpURLConnection but kept getting a FileNotFoundException even though the URL worked perfectly in my desktop browser. Here’s an example, without error catching stuff, of how the code could look like:

String user = getUser();
String url = "http://somesite.com/page?user=" + user;
URL u = new URL(url);
HttpURLConnection c = (HttpURLConnection) u.openConnection();
c.setDoInput(true);
c.setDoOutput(true);
c.connect();

InputStream is = c.getInputStream();

The problem was that at the last line the call to getInputStream generated a FileNotFoundException. I printed the URL that was used and tried it in the browser. Worked prefectly.

I managed to solve it though. The problem was that even though creating a URL object with the built URL string works, the URL might be broken. For example, if user is “Some guy” the url will contain a space which is not valid. Browsers solve this by automatically replacing the space with %20 which is what my browser did.

To solve this in code you use the URLEncoder class’ static method encode. This method takes a string and encodes it to a string that is ok to put in a URL. So replacing

String url = "http://somesite.com/page?user=" + user;

with

String url = "http://somesite.com/page?user=" + URLEncoder.encode(user, "UTF-8");

solves the problem when user contains illegal URL characters.

Hope this helps someone out there getting weird errors. 🙂