URLConnection problem

Dear Java Programmers,

I am just getting crazy with this stuff. I am asking for the length of a URLConnection, but sometimes the given URLOject has no information or the address doesn't exists. 

URL url = new URL("http://www.alientech.to/pic/exelixis03/Auto-Exelixis_045.JPG";);
URLConnection connection = url.openConnection();
//Then we ask for the length
int length = connection.getContentLength();


However, if the host is unknown the application stops in the last line without giving a time out. I have tried with a 	connection.setConnectTimeout(5000);   but I still have the same problem.

How Can I test the validity of a URL (something like a ping) without being blocked? If I am blocked with a URLConnection, how can interrumpt the channel ? Or even better, is it possible to close the "port" of this URLConnection ?

thanks a lot,

Marcelo

PS: I have already tried to make connection=null, but that doesn't work (the channel is still active).
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