ž®½ç®¡æˆ‘所知道的浏览器都支持cookie的设¾|®ï¼Œä¸è¿‡ç”¨æˆ·å¯ä»¥æœ‰æ„è¯†çš„ž®†å®ƒå…³é—­åQŒæˆ–者无意识的将它关闭。当你在你的servlets/JSP™åµé¢ä¸­ä‹É用cookieæ—Óž¼Œä½ ä¸èƒ½ä¿è¯ç”¨æˆïLš„‹¹è§ˆå™¨æ˜¯å¦å¯ä»¥æŽ¥å—cookieåQï¼ä½ éœ€è¦å…ˆ‹‚€æŸ¥ä¸€ä¸‹ã€‚这儿有一个检查用æˆïLš„‹¹è§ˆå™¨çš„cookie是否有效的小技巧ã€?/p>

˜q™ä¸ªæŠ€å·§å¾ˆ½Ž€å•ã€‚你从servlet或JSP向用æˆïLš„‹¹è§ˆå™¨å‘å‡ÞZ¸€ä¸ªHTTP回应åQŒå¼ºè¡Œä‹É‹¹è§ˆå™¨åœ¨½W¬äºŒ‹Æ¡è¿”回。在½W¬ä¸€‹Æ¡çš„响应中，你发å‡ÞZ¸€ä¸ªcookie。当‹¹è§ˆå™¨ç¬¬äºŒæ¬¡˜q”回的时候，‹‚€æŸ¥ä¸Šä¸€‹Æ¡å‘出的cookie。如果cookie存在åQŒè¯´æ˜Žæµè§ˆå™¨çš„cookie功能可用。否则说明用æˆïLš„‹¹è§ˆå™¨å¤ªè€ï¼Œä¸æ”¯æŒcookieåQŒæˆ–者浏览器的cookie功能被关闭ã€?/p>

JSP™åµé¢ç”¨ä¸‹é¢è¿™ŒDµä»£ç æ£€æŸ¥cookie是否有效。如果有效，那么™åµé¢çš„返回字½W¦ä¸²ä¸?#8220;Cookie is on”.若无效则ä¸?#8220;Cookie is off”:

<%
  if (request.getParameter("flag")==null) {
    // the first request
    Cookie cookie = new Cookie("cookieSetting", 
"on");
    response.addCookie(cookie);
    String nextUrl = request.getRequestURI() + 
"?flag=1";
    // force the browser to refresh
    out.println("<META HTTP-EQUIV=Refresh 
CONTENT=0;URL=" + nextUrl +">");
  }
  else {
    // the second request
    Cookie[] cookies = request.getCookies();
    boolean cookieFound = false;
    if (cookies!=null) {
      int length = cookies.length;
      for (int i=0; i<length; i++) {
        Cookie cookie = cookies[i];
        if 
(cookie.getName().equals("cookieSetting") &&
          cookie.getValue().equals("on")) {
          cookieFound = true;
          break;
        }
      }
    }
    if (cookieFound) {
      out.println("Cookie is on.");
    }
    else {
      out.println("Cookie is off.");
    }
  }
%>