–典型的请求头信息
–读取HTTP请求头
–使用表格显示所有请求头信息
–理解各种请求头的含义
–区分不同的浏览器类型
##############Michael分割线###################
• 典型的请求头信息
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• 读取HTTP请求头
–使用HttpServletRequest中的方法
• 一般方法
–getHeader (header名称不区分大小写)
–getHeaders
–getHeaderNames

• 专门方法
–getCookies
–getAuthType
–getRemoteUser
–getContentLength
–getContentType
–getDateHeader
–getIntHeader

• 相关信息
–getMethod
–getRequestURI
–getQueryString
–getProtocol
• 使用表格显示有请求头信息
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login.html
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">    
<html>    
    <head>    
        <title>login.html</title>    
        <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">    
        <meta http-equiv="description" content="this is my page">    
        <meta http-equiv="content-type" content="text/html; charset=UTF-8">    
        <!--<link rel="stylesheet" type="text/css" href="./styles.css">-->    

    </head>    
    <body>    
        <form name="f1" id="f1" action="/Servlet_RequestHeader/servlet/RequestHeaderServlet" method="post">    
            <table border="0">    
                <tr>    
                    <td>Login:</td>    
                    <td><input type="text" name="login" id="login"></td>    
                </tr>    
                <tr>    
                    <td>Password:</td>    
                    <td><input type="password" name="password" id="password"></td>    
                </tr>    
                <tr>    
                    <td colspan="2" align="center"><input type="submit" value="login"></td>    
                </tr>    
            </table>    
        </form>    
    </body>    
</html>
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RequestHeaderServlet.java
package com.michael.servlet;    

import java.io.IOException;    
import java.io.PrintWriter;    
import java.util.Enumeration;    

import javax.servlet.ServletException;    
import javax.servlet.http.HttpServlet;    
import javax.servlet.http.HttpServletRequest;    
import javax.servlet.http.HttpServletResponse;    

public class RequestHeaderServlet extends HttpServlet {    

        /**    
         * Constructor of the object.    
         */
    
        public RequestHeaderServlet() {    
                super();    
        }    

        /**    
         * Destruction of the servlet. <br>    
         */
    
        public void destroy() {    
                super.destroy(); // Just puts "destroy" string in log    
                // Put your code here    
        }    

        /**    
         * The doGet method of the servlet. <br>    
         *    
         * This method is called when a form has its tag value method equals to get.    
         *    
         * @param request the request send by the client to the server    
         * @param response the response send by the server to the client    
         * @throws ServletException if an error occurred    
         * @throws IOException if an error occurred    
         */
    
        public void doGet(HttpServletRequest request, HttpServletResponse response)    
                        throws ServletException, IOException {    

                doPost(request,response);    
        }    

        /**    
         * The doPost method of the servlet. <br>    
         *    
         * This method is called when a form has its tag value method equals to post.    
         *    
         * @param request the request send by the client to the server    
         * @param response the response send by the server to the client    
         * @throws ServletException if an error occurred    
         * @throws IOException if an error occurred    
         */
    
        public void doPost(HttpServletRequest request, HttpServletResponse response)    
                        throws ServletException, IOException {    
                Enumeration names = request.getHeaderNames();                

                response.setContentType("text/html");    
                PrintWriter out = response.getWriter();    
                out    
                                .println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");    
                out.println("<HTML>");    
                out.println("    <HEAD><TITLE>A Servlet</TITLE></HEAD>");    
                out.println("    <BODY>");    

                out.println("<table>");    
                out.println("<tr>");    
                out.println("<th>");    
                out.println("RequestHeader Name");    
                out.println("</th>");    
                out.println("<th>");    
                out.println("RequestHeader Value");    
                out.println("</th>");    
                out.println("</tr>");    
                while(names.hasMoreElements()){    
                        String name = (String) names.nextElement();    
                        String value = request.getHeader(name);    
                        out.println("<tr>");    
                        out.println("<td>");    
                        out.println(name);    
                        out.println("</td>");    
                        out.println("<td>");    
                        out.println(value);    
                        out.println("</td>");    
                        out.println("</tr>");    
                }    
                out.println("</table>");    
                out.println("    </BODY>");    
                out.println("</HTML>");    
                out.flush();    
                out.close();    
        }    

        /**    
         * Initialization of the servlet. <br>    
         *    
         * @throws ServletException if an error occure    
         */
    
        public void init() throws ServletException {    
                // Put your code here    
        }    

}
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看下效果
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• 理解各种请求头的含义
– Accept
• 标识浏览器能处理MIME类型
• 能发送不同的内容到不同的客户端. 例如,PNG文件有好的压缩特性,但是在浏览器中支持的不是很广泛。
• 一个Servlet可以检查是否支持PNG文件格式,如果支持
– <IMG SRC=“picture.png” ...> 否则
– <IMG SRC="picture.gif" ...>
– Accept-Encoding
• 标识浏览器能处理的编码类型
– Authorization
• 授权信息,通常出现在对服务器发送的WWW-Authenticate头的应答中
– Connection
• 表示是否需要持久连接。如果Servlet看到这里的值为“Keep-Alive”,或者看到请求使用的是HTTP 1.1(HTTP 1.1默认进行持久连接),它就可以利用持久连接的优点,当页面包含多个元素时(例如Applet,图片),显著地减少下载所需要的时间。要实现这一点,Servlet需要在应答中发送一个Content-Length头,最简单的实现方法是:先把内容写入ByteArrayOutputStream,然后在正式写出内容之前计算它的大小。
– Cookie
• 参考Java EE WEB工程师培训-JDBC+Servlet+JSP整合开发之16.Cookie
–Host
• 包含一个URL,用户从该URL代表的页面出发访问当前请求的页面
–If-Modified-Since
• 只有当所请求的内容,在指定的日期之后,又经过修改才返回它,否则返回304“Not Modified”应答
–Referer
• 包含一个URL,用户从该URL代表的页面出发访问当前请求的页面。
–User-Agent
• 浏览器类型,如果Servlet返回的内容与浏览器类型有关则该值非常有用。
• 区分不同的浏览器类型p_w_picpath
BrowserTypeServlet.java
package com.michael.servlet;    

import java.io.IOException;    
import java.io.PrintWriter;    

import javax.servlet.ServletException;    
import javax.servlet.http.HttpServlet;    
import javax.servlet.http.HttpServletRequest;    
import javax.servlet.http.HttpServletResponse;    

public class BrowserTypeServlet extends HttpServlet {    

        /**    
         * Constructor of the object.    
         */
    
        public BrowserTypeServlet() {    
                super();    
        }    

        /**    
         * Destruction of the servlet. <br>    
         */
    
        public void destroy() {    
                super.destroy(); // Just puts "destroy" string in log    
                // Put your code here    
        }    

        /**    
         * The doGet method of the servlet. <br>    
         *    
         * This method is called when a form has its tag value method equals to get.    
         *    
         * @param request the request send by the client to the server    
         * @param response the response send by the server to the client    
         * @throws ServletException if an error occurred    
         * @throws IOException if an error occurred    
         */
    
        public void doGet(HttpServletRequest request, HttpServletResponse response)    
                        throws ServletException, IOException {    

                doPost(request,response);    
        }    

        /**    
         * The doPost method of the servlet. <br>    
         *    
         * This method is called when a form has its tag value method equals to post.    
         *    
         * @param request the request send by the client to the server    
         * @param response the response send by the server to the client    
         * @throws ServletException if an error occurred    
         * @throws IOException if an error occurred    
         */
    
        public void doPost(HttpServletRequest request, HttpServletResponse response)    
                        throws ServletException, IOException {    
                String browserName = request.getHeader("user-agent");    
                String result="";    
                if(browserName.indexOf("MSIE")!=-1){    
                        result = "您当前使用的浏览器是IE!";    
                }else{    
                        result = "您当前使用的浏览器是FireFox!";    
                }    

                response.setContentType("text/html;charset=gbk");    
                PrintWriter out = response.getWriter();    
                out    
                                .println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");    
                out.println("<HTML>");    
                out.println("    <HEAD><TITLE>A Servlet</TITLE></HEAD>");    
                out.println("    <BODY>");    
                out.println(result);    
                out.println("    </BODY>");    
                out.println("</HTML>");    
                out.flush();    
                out.close();    
        }    

        /**    
         * Initialization of the servlet. <br>    
         *    
         * @throws ServletException if an error occure    
         */
    
        public void init() throws ServletException {    
                // Put your code here    
        }    

}
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测试
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OK!
##############Michael分割线###################