在网站开发中经常要用到cookie来存放一些用户信息,比如登录密码,购物列表啊等等
接下来简要剖析一下cookie
Cookies有以下几个特点:
1、只能是文本内容,而且长度不得大于4KB
2、客户端可以阻止cookie的写入,故而用cookie来实现功能存在一些不稳定因素
3、子路径设置的cookie,父路径不能读取,相反父路径设置的cookie,子路径可以读取。这一点十分重要,也比较容易犯错误。
接下来手动创建几个cookies:
package cookies; 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 { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { req.setCharacterEncoding("GBK"); resp.setContentType("text/html;charset=GBK"); for (int i = 0; i < 3; i++) { // 生成3个临时cookies,该cookie存放在内存中,一旦浏览器被关闭则被自动清除 Cookie cookie = new Cookie("Session-Cookie-" + i, "Cookie-Value-S" + i); // 将cookie放入应答消息中,返回给客户端,临时cookie就存放于客户端内存 resp.addCookie(cookie); // 生成3个有生命周期的cookie,存放于文本中(ie浏览器的cookie文本中),即使浏览器关闭也不会消失 cookie = new Cookie("Persisten-Cookie-" + i, "Cookie-Value-P" + i); // setMaxAge(int t)设置一个生命周期,t为其值,以秒为单位 cookie.setMaxAge(3600); // 将cookie放入应答消息中,返回给客户端,有生命周期的cookie就存放于客户端文本中 resp.addCookie(cookie); } // 启用一个输出流,将内容输出到页面上 PrintWriter out = resp.getWriter(); out .println("<html><head>" + "<meta http-equiv=\"content-type\" content=\"text/html; charset=gbk\">" + "<title>生成cookie</title>" + "</head>" + "<body><a href=\"Showcookies\">查看cookie</a>" + "</body></html>"); // 记得关闭输出流,节省开销 out.close(); } // 重写doPost方法,让其调用doGet方法 @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doGet(req, resp); } }
上面通过Setcookies产生6个cookies,接下来获取这6个cookies并且显示在页面上:
package cookies; 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 { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { // 设置编码方式 req.setCharacterEncoding("gbk"); resp.setContentType("text/html;charset=gbk"); // 用一个html表格来显示我们得到的cookie数据 String title = "Active Cookies"; PrintWriter out = resp.getWriter(); out .println("<html><head><title>" + "参数客户端Cookie" + "</title>" + "<meta http-equiv=\"content-type\" content=\"text/html; charset=gbk\">" + "</head>" + "<body bgcolor=\"#fdf5e6\">" +"<center>" + "<h1 align=\"center\">" + title + "</h1>\n" + "<table border=1 algin=\"center\">\n" + "<tr bgcolor=\"#ffad0o\">\n" + "<th>Cookie Name\n" + "<th>Cookie Value"); // 从客户端的请求中取本网站的cookie信息,此时http为连接状态 Cookie[] cookies = req.getCookies(); // 得到cookie信息,输出到页面上 if (cookies != null) { Cookie cookie; for (int i = 0; i < cookies.length; i++) { cookie = cookies[i]; out.println("<tr>\n" + "<td>" + cookie.getName() + "</td>\n" + "<td>" + cookie.getValue() + "</td>\n"); } out.println("</table><center></body></html>"); out.close(); } } }
xml配置文档:
<servlet> <servlet-name>Setcookies</servlet-name> <servlet-class>cookies.Setcookies</servlet-class> </servlet> <servlet-mapping> <servlet-name>Setcookies</servlet-name> <url-pattern>/Setcookies</url-pattern> </servlet-mapping> <servlet> <servlet-name>Showcookies</servlet-name> <servlet-class>cookies.Showcookies</servlet-class> </servlet> <servlet-mapping> <servlet-name>Showcookies</servlet-name> <url-pattern>/Showcookies</url-pattern> </servlet-mapping>
![关于cookie不得不说的事儿](http://img.e-com-net.com/image/product/5fb73169a7884cc9ae0b7d1d030624a1.png)
先启动Setcookies创建6个cookies,再启动Showcookies,成功显示了创建的6个cookies,其中最后一项应该是浏览器默认生成的,于我们的操作无关。
接下来解释:子路径设置的cookie,父路径不能读取,相反父路径设置的cookie,子路径可以读取。
修改xml配置文件如下:
<servlet> <servlet-name>Setcookies</servlet-name> <servlet-class>cookies.Setcookies</servlet-class> </servlet> <servlet-mapping> <servlet-name>Setcookies</servlet-name> <url-pattern>/Setcookies</url-pattern> </servlet-mapping> <servlet> <servlet-name>Showcookies</servlet-name> <servlet-class>cookies.Showcookies</servlet-class> </servlet> <servlet-mapping> <servlet-name>Showcookies</servlet-name> <url-pattern>/test/Showcookies</url-pattern> </servlet-mapping>
现在,Showcookies成为了url下的test子路径了,而Setcookies此时是一个父路径。执行程序,成功获取cookies信息。
继续更改xml文件:
<servlet> <servlet-name>Setcookies</servlet-name> <servlet-class>cookies.Setcookies</servlet-class> </servlet> <servlet-mapping> <servlet-name>Setcookies</servlet-name> <url-pattern>/test/Setcookies</url-pattern> </servlet-mapping> <servlet> <servlet-name>Showcookies</servlet-name> <servlet-class>cookies.Showcookies</servlet-class> </servlet> <servlet-mapping> <servlet-name>Showcookies</servlet-name> <url-pattern>/Showcookies</url-pattern> </servlet-mapping>
现在Setcookies成了URL的子路径test下的servlet,而Showcookies为父路径,执行Showcookies此时已经无法获取cookies信息了。