Cookie的使用
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一、cookie的作用
在我们平常写的B/S程序中，会经常用到cookie，主要有以下一些作用：
1、?记录用户名和密码
以及该用户需要保存的一些信息，如购物购站，使用cookie，可以让用户自动登录到站点等。
2、?定制站点
可以使用cookie来记录用户的偏好。
3、?定向广告
可以使用cookie来记录用记经常访问的主题，并向他们显示与这些主题相关的广告。
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二、向客户程序发送cookie
1、?创建cookie对象
Cookie c = new Cookie(“userId”,”landril”);
2、?设置最大时效，默认该cookie是存储在浏览器的内在中，用户关闭浏览器则被删除，下面的方法是将cookie存储在硬盘上。
c.setMaxAge(60*60*24);//一天，如果设置为0则是删除该cookie
3、?将cookie放入到HTTP响应报头，可以使用HttpServletResponse的addCookie方法，此方法不修改之前指定的Set-Cookie报头，而是创建新的报头。
response.addCookie(c);
?????? 注意：设置cookie的步骤为创建cookie对象，设置最大时效，将cookie放入响应报头，即发送到客户程序，记住一定要将cookie发送到客户程序
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三、从客户端读取cookie
1、?调用HttpServletRequest的getCookies得到一个Cookie对象的数组
2、?对数组进行循环，调用cookie的getName方法，获取具体的cookie的值
Cookie[] cookies = request.getCookies();
if(cookies != null){
for(int i=0;i<cookies.length;i++){
??????? Cookie c = cookies[i];
??????? if(“userId”.equals(c.getName())){
??????? System.out.println(c.getValue());
}
}
}
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四、cookie的常用方法
1、?setComment()/getComment()：指定或查找与该cookie相关的注释
2、?setDomain()/getDomain()：设置或读取该cookie适用的域
3、?setMaxAge()/getMaxAge()：操作cookie保留的时间，多长时间后过期
4、?getName()：读取cookie的名称
5、?setPath()/getPath()：设置或取得cookie适用的路径
cookie.setPath(“/”);指定服务器的所有页面都应该收到该cookie
6、?setSource()/getSource()：指定cookie是否只能通过加密连接（SSL）
默认false，表示cookie适用所有连接
7、?setValue()/getValue()：指定或获取cookie的值
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五、使用cookie
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1、RepeatServlet.java
public class RepeatServlet extends HttpServlet {
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??? public void doGet(HttpServletRequest request, HttpServletResponse response)
?????? ??? throws ServletException, IOException {
??? ??? boolean newa = true;
??? ??? Cookie[] cookies = request.getCookies();
??? ??? if(cookies != null){
?????? ??? for (int i = 0; i < cookies.length; i++) {
?????????? ??? Cookie c = cookies[i];
?????????? ??? if ((c.getName().equals("repeat")) && (c.getValue().equals("true"))) {
?????????? ?????? newa = false;
?????????? ??? ??? break;
?????????? ??? }
?????????? }
?????? }
??????
??? ??? String title;
?????? if (newa) {
?????? ??? Cookie rtn = new Cookie("repeat"," true");
?????? ??? rtn.setMaxAge(60*60*24*365);
?????? ??? response.addCookie(rtn);
?????? ??? title = "First Welcome";
?????? } else {
?????? ??? title = "Welcom Back";
?????? }
??????
??? ??? response.setContentType("text/html");
??? ??? PrintWriter out = response.getWriter();
??? ??? out.println("<html><body><h3>");
??? ??? out.println(title);
??? ??? out.println("</h3></body></html>");
??? }
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??? public void doPose(HttpServletRequest request, HttpServletResponse response)
?????? ??? throws ServletException, IOException {
??? ??? doGet(request,response);
??? }
}
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2、CookieUtil.java
public class CookieUtil{
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??? public static String getValue(HttpServletRequest request,String cName,String value){
??? ??? Cookie[] cookies = request.getCookies();
??? ??? if(cookies != null){
?????? ??? for (int i = 0; i < cookies.length; i++) {
?????????? ??? Cookie cookie = cookies[i];
?????????? ??? if (cName.equals(cookie.getName())) {
?????????? ??? ??? return cookie.getValue();
?????????? ??? }
?????????? }
?????? }
??? ??? return value;
??? }
???
??? public static Cookie getCookie(HttpServletRequest request,String cName){
??? ??? Cookie[] cookies = request.getCookies();
??? ??? if(cookies != null){
?????? ??? for (int i = 0; i < cookies.length; i++) {
?????????? ??? Cookie cookie = cookies[i];
?????????? ??? if (cName.equals(cookie.getName())) {
?????????? ??? ??? return cookie;
?????????? ??? }
?????????? }
?????? }
??? ??? return null;
??? }
}
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3、AccessCountServle.java 记录访问数
public class AccessCountServlet extends HttpServlet {
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??? public void doGet(HttpServletRequest request, HttpServletResponse response)
?????? ??? throws ServletException, IOException {
??????
??? ??? String acount = CookieUtil.getValue(request, "acc", "1");
?????? int count = Integer.parseInt(acount);
??? ??? Cookie cookie = new Cookie("acc",String.valueOf(count+1));
??? ??? cookie.setMaxAge(60*60*24*365);
??? ??? response.addCookie(cookie);
??????
??? ??? response.setContentType("text/html");
??? ??? PrintWriter out = response.getWriter();
??? ??? out.println("<html><body>Hello,the number is<h3>");
??? ??? out.println(count);
??? ??? out.println("</h3></body></html>");
??? }
???
??? public void doPost(HttpServletRequest request, HttpServletResponse response)
??? throws ServletException, IOException {
??? ??? doGet(request,response);
??? }
}