Networking code sometimes throws UnknownHostException

Question

I am trying to data from a server. Sometimes my code fails due to an UnknownHostException. Why is that? What is the cause of this problem?

Answer 1

I too am seeing sporadic UnknownHostExceptions in Java for no apparent reason. The solution is just to retry a few times. Here is a wrapper for DocumentBuilder.parse that does this:

static Document DocumentBuilder_parse(DocumentBuilder b, String uri) throws SAXException, IOException {
  UnknownHostException lastException = null;
  for (int tries = 0; tries < 2; tries++) {
    try {
      return b.parse(uri);
    } catch (UnknownHostException e) {
      lastException = e;
      System.out.println("Retrying because of: " + e);
      continue;
    }
  }
  throw lastException;
}