cookie是一小块可以嵌入在HTTP请求和应答中的数据。典型情况下，Web服务器将cookie值嵌入到应答的首部，而浏览器则在其以后的请求中都将携带同样的cookie。cookie的信息中可以有一部分用来存储会话ID，这个ID被服务器用来将某些HTTP请求绑定在会话中。cookie由浏览器保存在客户端，通常保存在一个名为cookie.txt的文件。cookie还含有一些其他属性，诸如可选的注释、版本号以及最长生存期。下面为cookies servlet的代码，它显示了当前请求的首部所包含的所有cookie的一些信息。
1 import javax.servlet.*; 2 import javax.servlet.http.*; 3 4 /** 5 * <p>This is a simple servlet that displays all of the 6 * Cookies present in the request 7 */ 8 public class Cookies extends HttpServlet 9 { 10 11 /** 12 * <p>Performs the HTTP GET operation 13 * 14 * @param req The request from the client 15 * @param resp The response from the servlet 16 */ 17 public void doGet(HttpServletRequest req, 18 HttpServletResponse resp) 19 throws ServletException, java.io.IOException 20 { 21 22 // Set the content type of the response 23 resp.setContentType("text/html"); 24 25 // Get the PrintWriter to write the response 26 java.io.PrintWriter out = resp.getWriter(); 27 28 // Get an array containing all of the cookies 29 Cookie cookies[] = req.getCookies(); 30 31 // Write the page header 32 out.println("<html>"); 33 out.println("<head>"); 34 out.println("<title>Servlet Cookie Information</title>"); 35 out.println("</head>"); 36 out.println("<body>"); 37 38 if ((cookies == null) || (cookies.length == 0)) { 39 out.println("No cookies found"); 40 } 41 else { 42 out.println("<center><h1>Cookies found in the request</h1>"); 43 44 // Display a table with all of the info 45 out.println("<table border>"); 46 out.println("<tr><th>Name</th><th>Value</th>" + 47 "<th>Comment</th><th>Max Age</th></tr>"); 48 49 for (int i = 0; i < cookies.length; i++) { 50 Cookie c = cookies[i]; 51 out.println("<tr><td>" + c.getName() + "</td><td>" + 52 c.getValue() + "</td><td>" + 53 c.getComment() + "</td><td>" + 54 c.getMaxAge() + "</td></tr>"); 55 } 56 out.println("</table></center>"); 57 } 58 // Wrap up 59 out.println("</body>"); 60 out.println("</html>"); 61 out.flush(); 62 } 63 }
web.xml的配置中加入
<servlet>
<servlet-name>Cookies</servlet-name>
<servlet-class>Cookies</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>Cookies</servlet-name>
<url-pattern>/servlets/servlet/Cookies</url-pattern>
</servlet-mapping>
在浏览器中输入http://localhost:9090/examples/servlets/servlet/Cookies会看到结果