import java.io.IOException;  import java.util.LinkedList;  import java.util.List;  import java.util.Queue;  import java.util.regex.Matcher;  import java.util.regex.Pattern;    import org.jsoup.Jsoup;  import org.jsoup.nodes.Document;  import org.jsoup.nodes.Element;  import org.jsoup.select.Elements;    public class Robot {        // robot url      private List<String> urlList;      // cache url      private Queue<String> urlQueue;      // define Host      public final static String HOST = "debugs.tk";        // constructor      public Robot() {          super();          // initialization robot's member          setUrlList(new LinkedList<String>());          setUrlQueue(new LinkedList<String>());      }        // url      public List<String> getUrlList() {          return urlList;      }        public void setUrlList(List<String> urlList) {          this.urlList = urlList;      }        // cache      public Queue<String> getUrlQueue() {          return urlQueue;      }        public void setUrlQueue(Queue<String> urlQueue) {          this.urlQueue = urlQueue;      }        // Legal link      private boolean isURL(String url) {          try {              // judge url              Pattern pattern = Pattern.compile("^[a-zA-z]+://[^\\s]*");              Matcher matcher = pattern.matcher(url);              if (matcher.matches()) {                  return true;              } else {                  return false;              }          } catch (Exception e) {              e.printStackTrace();              return false;          }      }        // whether the url is belong to host      public static boolean isHost(String url) {          return url.contains(HOST);      }        // travel all url      public void traverse(String seed) {            for (this.getUrlQueue().add(seed); !this.getUrlQueue().isEmpty();) {              boolean flag = true;              Document document = null;              try {                  document = Jsoup.connect(seed).timeout(5000).get();              } catch (IOException e) {                  e.printStackTrace();                  // whether connect success                  flag = false;              }              // whether connect success,then select a tag              // add these aTag into queue              if (flag) {          // get url                  Elements elements = document.select("a[href]");                  for (Element e : elements) {                      String s = e.attr("abs:href");                      // Legal link and belong host                      // and url not in list                      // then add it                      if (isURL(s) && s.contains(HOST)                              && (!getUrlQueue().contains(s))                              && (!getUrlList().contains(s))) {                          this.getUrlQueue().add(s);                      }                  }              }              // get head of queue              // and set it seed              // travel seed it again              seed = this.getUrlQueue().poll();              this.getUrlList().add(seed);              // show information              // System.out.println("SIZE:"               // + this.getUrlQueue().size() + "---"              // + seed + " connect!");          }      }  }