Tecnologie Web: Parte 6c [Giovedý, 4 Maggio 2006]

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LinkTracker

Per invocare la classe LinkTracker, dobbiamo utilizzare dei link opportuni come ad esempio in questo file HTML:

<html>
<head>
    <title>Some Links Tracked by the LinkTracker Servlet</title>
</head>
<body>
    Some good links for Servlets and JSP. Each link is directed through the
    LinkTracker Servlet. Click on a few and visit the
    <a href="LinkTracker.java">LinkTracker Servlet</a>.
    <ul>
        <li><a href="LinkTracker.java?link=http://www.jspbook.com"> Servlets and JSP
        Book Support Site</a></li>
        <li><a href="LinkTracker.java?link=http://www.jspinsider.com"> JSP Insider</a></li>
        <li><a href="LinkTracker.java?link=http://java.sun.com"> Sun Microsystems</a></li>
    </ul>
</body>
</html>

Il listato completo della classe (aggiornato a Java 1.5) Ŕ:


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

public class LinkTracker extends HttpServlet {
	
	static private Hashtable hashLinks = new Hashtable();
	String tstamp;
	
	public LinkTracker() {
		tstamp = new Date().toString();
	}
	
	public void doGet(HttpServletRequest request, 
			HttpServletResponse response) throws IOException, ServletException {
		
		String questoLink = request.getParameter("link");
		if (questoLink != null && !questoLink.equals("")) {
			synchronized (hashLinks){
				Integer count = (Integer) hashLinks.get(questoLink);
				if (count == null) {
					hashLinks.put(questoLink, new Integer(1));
				}
				else {
					hashLinks.put(questoLink, new Integer(1+count.intValue()));
				}
			}
			response.sendRedirect(questoLink);
		}
		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 (hashLinks.size() != 0) {
				Enumeration enumLinks = hashLinks.keys();
				while (enumLinks.hasMoreElements()) {
					String key = (String)enumLinks.nextElement();
					int count = ((Integer)hashLinks.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);
	}
}

ShowHeaders


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

public class ShowHeaders extends HttpServlet {

  public void doGet(HttpServletRequest request,
                    HttpServletResponse response)
    throws IOException, ServletException {
      response.setContentType("text/html");
      PrintWriter out = response.getWriter();
      out.println("<html>");
      out.println("<head>");
      out.println("<title>Request's HTTP Headers</title>");
      out.println("</head>");
      out.println("<body>");
      out.println("<p>HTTP headers sent by your client:</p>");
      Enumeration listaNomiHeader = request.getHeaderNames();
      while (listaNomiHeader.hasMoreElements()) {
        String headerName = (String) listaNomiHeader.nextElement();
        String headerValue = request.getHeader(headerName);
        out.print("<b>"+headerName + "</b>: ");
        out.println(headerValue + "<br>");
      }
      out.println("</body>");
      out.println("</html>");
  }
}

ShowParameters


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

public class ShowParameters extends HttpServlet {

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

    response.setContentType("text/html");
    PrintWriter out = response.getWriter();
    out.println("<html>");
    out.println("<head>");
    out.println("<title>Request HTTP Parameters Sent</title>");
    out.println("</head>");
    out.println("<body>");
    out.println("<p>Parameters sent with request:</p>");
    Enumeration listaNomiParametri = request.getParameterNames();
    while (listaNomiParametri.hasMoreElements()) {
      String pName = (String) listaNomiParametri.nextElement();
      String[] pValues = request.getParameterValues(pName);
      out.print("<b>"+pName + "</b>: ");
      for (int i=0;i<pValues.length;i++) {
        out.print(pValues[i]);
      }
      out.print("<br>");
    }
    out.println("</body>");
    out.println("</html>");
  }
  public void doPost(HttpServletRequest request,
                    HttpServletResponse response)
    throws IOException, ServletException {
    doGet(request, response);
  }
}