url rewriting
URL rewriting是一种session tracking技术。
它在url后面添加一个或多个token，token是键值对的形式。通过这些键值对来保存信息。
url?key-1=value-1&key-2=value-2 ... &key-n=value-n
适用于被保存的信息不需要在太多的page中使用，且被保存的信息不敏感的情况。 例:
@WebServlet(name = "Top10Servlet", urlPatterns = { "/top10" })
public class Top10Servlet extends HttpServlet {
private static final long serialVersionUID = 987654321L;
private List<String> londonAttractions = new ArrayList<>(10);
private List<String> parisAttractions = new ArrayList<>(10);
@Override
public void init() throws ServletException {
londonAttractions.add("Buckingham Palace");
londonAttractions.add("London Eye");
londonAttractions.add("British Museum");
londonAttractions.add("National Gallery");
londonAttractions.add("Big Ben");
londonAttractions.add("Tower of London");
londonAttractions.add("Natural History Museum");
londonAttractions.add("Canary Wharf");
londonAttractions.add("2012 Olympic Park");
londonAttractions.add("St Paul's Cathedral");
parisAttractions.add("Eiffel Tower");
parisAttractions.add("Notre Dame");
parisAttractions.add("The Louvre");
parisAttractions.add("Champs Elysees");
parisAttractions.add("Arc de Triomphe");
parisAttractions.add("Sainte Chapelle Church");
parisAttractions.add("Les Invalides");
parisAttractions.add("Musee d'Orsay");
parisAttractions.add("Montmarte");
parisAttractions.add("Sacre Couer Basilica");
}
@Override
public void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException,
IOException {
String city = request.getParameter("city");
if ("london".equals(city) || "paris".equals(city)) {
// show attractions
showAttractions(request, response, city);
} else {
// show main page
showMainPage(request, response);
}
}
private void showMainPage(HttpServletRequest request,
HttpServletResponse response) throws ServletException,
IOException {
response.setContentType("text/html");
PrintWriter writer = response.getWriter();
writer.print("<!DOCTYPE html><html><head>" +
"<title>Top 10 Tourist Attractions</title>" +
"</head><body>" +
"Please select a city:" +
"<br/><a href='?city=london'>London</a>" +
"<br/><a href='?city=paris'>Paris</a>" +
"</body></html>");
}
private void showAttractions(HttpServletRequest request,
HttpServletResponse response, String city)
throws ServletException, IOException {
int page = 1;
String pageParameter = request.getParameter("page");
if (pageParameter != null) {
try {
page = Integer.parseInt(pageParameter);
} catch (NumberFormatException e) {
// do nothing and retain default value for page
}
if (page > 2) {
page = 1;
}
}
List<String> attractions = null;
if ("london".equals(city)) {
attractions = londonAttractions;
} else if ("paris".equals(city)) {
attractions = parisAttractions;
}
response.setContentType("text/html");
PrintWriter writer = response.getWriter();
writer.println("<!DOCTYPE html><html><head>" +
"<title>Top 10 Tourist Attractions</title>" +
"</head><body>");
writer.println("<a href='top10'>Select City</a> ");
writer.println("<hr/>Page " + page + "<hr/>");
int start = page * 5 - 5;
for (int i = start; i < start + 5; i++) {
writer.println(attractions.get(i) + "<br/>");
}
writer.print("<hr style='color:blue'/>" +
"<a href='?city=" + city +
"&page=1'>Page 1</a>");
writer.println(" <a href='?city=" + city +
"&page=2'>Page 2</a>");
writer.println("</body></html>");
}
}