title: Controlling the list of URL(s) to be crawled at runtime
body: <p>In crawler4j we can override a function <code>boolean shouldVisit(WebUrl url)</code> and control whether that particular url should be allowed to be crawled by returning 'true' and 'false'. </p>
  
  <p>But can we add URL(s) at runtime ? if yes , what are ways to do that ?
  Currently I can add URL(s) at beginning of program using <code>addSeed(String url)</code> function before the <code>start(BasicCrawler.class, numberOfCrawlers)</code> in <code>CrawlController</code> class and if I try to add new url using <code>addSeed(String url)</code>, it gives error. <a href="http://imgur.com/bxvKx" rel="nofollow">Here</a> is error image .</p>
  
  <p>Any help will be appreciative and please let me know if any more detail about project is required to answer the question .  </p>