Thread framework question (java)

Create a simple webcrawler which pings & crawls a number of websites (read from an xml file)
The number of threads executing the crawler should remain the same until the threads are finished. e.g. if the crawler dies it should restart
There is no need to cater for timeouts.

ExecutorService exec = Executors.newFixedThreadPool(numberOfThreads);

List<URL> listOfURLs = new ArrayList<URL>();
listOfURLs  = getURLList(); // read from some source
List<CrawlResult> = new ArrayList<CrawlResult>();
ExecutorService exec = Executors.newFixedThreadPool(numberOfThreads);
int failureCount = 0;
while ( !listOfURLs.isEmpty && failureCount < MAX_FAIL) {
	for (URL url: listOfURLs) {
		exec.execute(new MyRunnableCrawl(url));
		//MyRunnable will contain the crawl code and if fail add URL to a synchronised failedURL list	
	}
        listOfURLs.clear();
	//tell the exec after these URLs we are done
	exec.shutdown();
	try {
		boolean b = exec.awaitTermination(60, TimeUnit.SECONDS); // no need to cater for timeout exceptions
	} catch (InterruptedException e) { e.printStackTrace(); }
	//resassign the list of URLS to crawl to the ones which have failed (if any)
	listOfURLs = getFailureList();
	failureCount++;
}