Les exceptions postconditions sous Android

Bonjour
Voici un exemple d'utilisation des exceptions postconditions sous Android:

public String login(String username, String password) throws IOException
{
if (username == null) throw new IllegalArgumentException("Username cannot be null");
if (password == null) throw new IllegalArgumentException("Password cannot be null");

try {
HttpClient client = new DefaultHttpClient();

String url = String.format("https://my.webservice.com/login.php?user=%0&pwd=%1",username,password); //$NON-NLS-1$

HttpGet getRequest = new HttpGet(url);
HttpResponse response = client.execute(getRequest);

if (response.getStatusLine().getStatusCode()>=400)
throw new IOException(response.getStatusLine().getReasonPhrase());

HttpEntity entity = response.getEntity();
String token = entity.toString();
if ("ERROR".equalsIgnoreCase(token))
return null;

return token;
} catch (ClientProtocolException ex) {
throw new IllegalStateException("HTTPS non supporté !",ex);
}
}