Java EE WEB工程师培训-JDBC+Servlet+JSP整合开发之14.Servlet请求头信息-优快云博客

–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

• 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

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>

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
        }

}

看下效果

• 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

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
        }

}