Cookie是web服务器发送到浏览器的间断文本信息,以后在访问同一个web站点或域时浏览器就会毫无更改的返回该文本信息,通过让服务器读取以前发送到客户端的信息,站点就能为访问者提供许多方便,例如无需重新登录.

资料源自于《Servlet与JSP核心技术》,我看完后,重新敲一遍以便于增加理解.

设置和读取cookie的例子

import java.io.IOException;
import java.io.PrintWriter;import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;public class SetCookies extends HttpServlet {private static final long serialVersionUID = 2380669421746720857L;@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {for(int i = 0; i < 3; i++) {Cookie cookie = new Cookie("Session-Cookie-"+i, "Cookie-Value-S"+i);resp.addCookie(cookie);cookie = new Cookie("Persistent-Cookie-"+i, "Cookie-Value-P"+i);cookie.setMaxAge(3600);resp.addCookie(cookie);}PrintWriter out = resp.getWriter();out.print("<a href=\"/SetCookies/ShowCookies\">show the cookies</a>");}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {doGet(req, resp);}}

以上是设置cookie,session cookie表示当前的cookie,没有设定时间,默认时间为负数。

persistent cookie表示持久性的cookie,设定时间为一小时.

测试目的,关闭浏览器后重新打开,理应看到persistent cookie;

showCookies.java如下

import java.io.IOException;
import java.io.PrintWriter;import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;public class ShowCookies extends HttpServlet {private static final long serialVersionUID = 2380669421746720857L;@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {Cookie[] cookies = req.getCookies();StringBuilder table = new StringBuilder();for(int i = 0; i < cookies.length; i++) {table.append("<table border = 1 align = \"center\"><tr><th>Cookie Name</th><th>Cookie value</th></tr>");table.append("<tr><td>"+cookies[i].getName()+"</td><td>"+cookies[i].getValue()+"</td></tr>");}PrintWriter out = resp.getWriter();out.print(table);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {doGet(req, resp);}}

程序跑起来如下

设置cookies

显示cookies

关掉浏览器重新打开

直接浏览网址http://localhost:8080/SetCookies/ShowCookies

可以看到预期效果

persistent cookie生效了.

源码地址http://www.oschina.net/code/snippet_778987_18392

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