轉發
request.getRequestDispatcher("/servlet/ListCartServlet").forward(request, response);
response.sendRedirect(url);
================== SESSION ==================
自動加jsessionid
response.encodeURL(url)
response.encodeRedirectURL(url)
======================================
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
HttpSession session = request.getSession();
List<Book> list = (List) session.getAttribute("list");
if(list==null || list.size()==0){
out.write("對不起，您還沒有購買任何商品!!");
return;
}
//顯示用戶買過的商品
out.write("您買過如下商品:<br>");
for(Book book : list){
out.write(book.getName() + "<br/>");
}
======================================
向session存入list
List list = (List) session.getAttribute("list"); //得到用戶用於保存所有書的容器
if(list==null){
list = new ArrayList();
session.setAttribute("list", list);
}
list.add(book);
================== 利用 Session 控制表單重複提交 ==================
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
boolean b = isToken(request); //判斷用戶是否是重複提交
if(b==true){
System.out.println("請不要重複提交");
return;
}
request.getSession().removeAttribute("token");
System.out.println("處理用戶提交請求！！");
}
private boolean isToken(HttpServletRequest request) {
String client_token = request.getParameter("token");
if(client_token==null){
return true;
}
String server_token = (String) request.getSession().getAttribute("token");
if(server_token==null){
return true;
}
if(!client_token.equals(server_token)){
return true;
}
return false;
}
/負責產生表單
public class FormServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
String token = TokenProccessor.getInstance().makeToken();
request.getSession().setAttribute("token", token); //在服務器端保存隨機數
out.println("<form action='/day07/servlet/DoFormServlet' method='post'>");
out.write("<input type='hidden' name='token' value='"+token+"'>");
out.println("用戶名:<input type='text' name='username'>");
out.println("<input type='submit' value='提交'>");
out.println("</form>");
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
class TokenProccessor{
/*
*單態設計模式（保證類的對象在內存中只有一個）
*1、把類的構造函數私有
*2、自己創建一個類的對象
*3、對外提供一個公共的方法，返回類的對象
*
*/
private TokenProccessor(){}
private static final TokenProccessor instance = new TokenProccessor();
public static TokenProccessor getInstance(){
return instance;
}
public String makeToken(){ //checkException
// 7346734837483 834u938493493849384 43434384
String token = (System.currentTimeMillis() + new Random().nextInt(999999999)) + "";
//數據指紋 128位長 16個字節 md5
try {
MessageDigest md = MessageDigest.getInstance("md5");
byte md5[] = md.digest(token.getBytes());
//base64編碼--任意二進制編碼明文字符 adfsdfsdfsf
BASE64Encoder encoder = new BASE64Encoder();
return encoder.encode(md5);
} catch (NoSuchAlgorithmException e) {
throw new RuntimeException(e);
}
}
}