Example

try {
  URL u = new URL("http://www.sdexpo.com/");
  URLConnection uc = u.openConnection();
  uc.connect();
  String key=null;
  for (int n = 1; 
       key=uc.getHeaderFieldKey(n)) != null; 
       n++) {
    System.out.println(key + ": " + uc.getHeaderField(key));
  }
}
catch (IOException e) {
 System.err.println(e);
}