
import java.util.*;
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class LinkTracker extends HttpServlet {
  static private Hashtable links = new Hashtable();

  String tstamp;
  public LinkTracker() {
    tstamp = new Date().toString();
  }

  public void doGet(HttpServletRequest request,
                    HttpServletResponse response)
    throws IOException, ServletException {

    String link = request.getParameter("link");
    if (link != null && !link.equals("")) {
      synchronized (links){
        Integer count = (Integer) links.get(link);
        if (count == null) {
          links.put(link, new Integer(1));
        }
        else {
          links.put(link, new Integer(1+count.intValue()));
        }
      }
      response.sendRedirect(link);
    }
    else {
      response.setContentType("text/html");
      PrintWriter out = response.getWriter();
      request.getSession();
      out.println("<html>");
      out.println("<head>");
      out.println("<title>Links Tracker Servlet</title>");
      out.println("</head>");
      out.println("<body>");
      out.println("<p>Links Tracked Since");
      out.println(tstamp+":</p>");
      if (links.size() != 0) {
        Enumeration enumeration = links.keys();
        while (enumeration.hasMoreElements()) {
          String key = (String)enumeration.nextElement();
          int count = ((Integer)links.get(key)).intValue();
          out.println(key+" : "+count+" visits<br>");
        }
      }
      else {
        out.println("No links have been tracked!<br>");
      }
      out.println("</body>");
      out.println("</html>");
    }
  }
  public void doPost(HttpServletRequest request,
                    HttpServletResponse response)
    throws IOException, ServletException {
    doGet(request, response);
  }
}