java - Blocking operations in URLConnection

Question

Running the following code snippet:

URL url = new URL(uri);
URLConnection urlconn = url.openConnection();
urlconn.connect();
urlconn.getContentLength();

I get the dead-lock sometimes, usually at two lines: urlconn.connect() and urlconn.getContentLength(). Also, when I do

InputStream is = urlconn.getInputStream();
// doing some reading
is.close();

I also get blocking at is.close(). I want to ask why such blocking happens. It is clueless to me from the Java API.