写入客户端的Cookie一般有两种,一种是不设置生存周期的Cookie,一种是设置了生存周期的Cookie。前者随着当前打开的浏览器窗口的存活而存活,当浏览器窗口关闭之后,Cookie随之消失。另一种Cookie在被设置生存周期后写入到了本地的磁盘文件中,存活时间由设定的时间决定,即使关闭窗口Cookie也不会消失。
以下两段代码来做实验。
SetCookie.java
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 SetCookie extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
for(int i=0;i<3;++i){
Cookie cookie = new Cookie("key"+i,"value"+i);//没有设置生存周期的Cookie,关闭浏览器窗口后消失
resp.addCookie(cookie);
cookie = new Cookie("mypersistentk"+i,"mypersistentv"+i);
cookie.setMaxAge(3600);//设置生存时间为一个小时,被写入到了磁盘文件中保存起来
resp.addCookie(cookie);
}
PrintWriter pw = resp.getWriter();
pw.print("<a href='http://localhost:8080:test/servlet/ShowCookie'>go</a>");
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req,resp);
}
}
ShowCookie.java
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 ShowCookie extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
PrintWriter pw = resp.getWriter();
Cookie[] cookies = req.getCookies();//打印出之前设置的Cookie
for(int i=0;i<cookies.length;++i){
Cookie cookie = cookies[i];
pw.println(cookie.getName()+":"+cookie.getValue());
pw.println();
}
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
}
}
运行SetCookie再运行ShowCookie后会打印出6条Coookie,包括没有生存周期的和有生存周期的。当关闭当前窗口,重新打开一个窗口再运行ShowCookie时只会出现三条Cookie记录,也就是之前设置生存周期被存入磁盘文件的那三条,而没有设置生存周期的另外三条Cookie随着浏览器窗口的关闭而死亡。
注意:在当前窗口打开的子窗口,即。按下Ctrl+n键时出现的窗口能够获得其父窗口的Cookie,包括没有设置生存周期的Cookie
补充:servlet/jsp设置的Cookie只能被当前路径以及其子路径下的sevlet/jsp读取到(这里的路径指的是url地址,即web.xml里配置的url-pattern)