javaweb学习总结二十(http响应)

一：http响应

1：http响应的组成部分

状态行、响应头、空行、响应数据

2：状态行

常用状态码：

200：请求成功

302：请求路径已经转移，请访问别的地址

307或者304： 请访问缓存信息

404：访问资源不存在

403：资源存在，但是没有访问权限

500：服务器内部错误

二：HTTP协议响应头

1：常用响应头

2:常用响应头分析演示

1）：location：http://www.it315.org/index.jsp   和403搭配使用，告诉浏览器重定向到其他的页面

代码如下：

 public class ServletDemo extends HttpServlet {

     public void doGet(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         doPost(request, response);
     }

     public void doPost(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         response.setStatus(302); // 302状态码代表资源路径转移，重定向到新的资源路径
         response.setHeader("location", "/servletDemo/1.html");

     }

 }

web.xml配置：

 <?xml version="1.0" encoding="UTF-8"?>
 <web-app version="2.5"
     xmlns="http://java.sun.com/xml/ns/javaee"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
     http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
   <servlet>
     <description>This is the description of my J2EE component</description>
     <display-name>This is the display name of my J2EE component</display-name>
     <servlet-name>ServletDemo</servlet-name>
     <servlet-class>com.hlcui.servlet.ServletDemo</servlet-class>
   </servlet>

   <servlet-mapping>
     <servlet-name>ServletDemo</servlet-name>
     <url-pattern>/servlet/ServletDemo</url-pattern>
   </servlet-mapping>

   <welcome-file-list>
     <welcome-file>index.jsp</welcome-file>
   </welcome-file-list>
 </web-app>

tomcat服务器启动后，访问路径：http://localhost:8080/servletDemo/servlet/ServletDemo

2）：Server  Apache tomcat  告诉浏览器服务器的类型信息

3）：Content-Encoding：gzip  告诉浏览器服务器回送数据的压缩类型

4）：Content-Length： 80   告诉浏览器呢服务器回送数据大小

演示代码如下：

 public class ServletDemo extends HttpServlet {

     public void doGet(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         doPost(request, response);
     }

     public void doPost(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         String content = "wertyuiopdfghjkl;dfghjklertyuiodfghjkcvbnmcvb"
                 + "wertyuiopdfghjkl;dfghjklertyuiodfghjkcvbnmcvbtyuiopvbhnjk"
                 + "wertyuiopdfghjkl;dfghjklertyuiodfghjkcvbnmcvbtyuiopvbhnjk"
                 + "wertyuiopdfghjkl;dfghjklertyuiodfghjkcvbnmcvbtyuiopvbhnjk"
                 + "wertyuiopdfghjkl;dfghjklertyuiodfghjkcvbnmcvbtyuiopvbhnjk"
                 + "wertyuiopdfghjkl;dfghjklertyuiodfghjkcvbnmcvbtyuiopvbhnjk"
                 + "wertyuiopdfghjkl;dfghjklertyuiodfghjkcvbnmcvbtyuiopvbhnjk";

         System.out.println("压缩前数据大小：" + content.getBytes().length);
         ByteArrayOutputStream array = new ByteArrayOutputStream();
         GZIPOutputStream gzip = new GZIPOutputStream(array);
         gzip.write(content.getBytes()); // 将内容进行压缩
         gzip.close();

         System.out.println("压缩后数据大小：" + array.size());
         // 告诉浏览器数据压缩格式以及大小
         response.setHeader("Content-Encoding", "gzip");
         response.setHeader("Content-Length", array.size() + "");
         // 将内容写到浏览器
         response.getOutputStream().write(array.toByteArray());

     }

 }

启动tomcat服务器，访问路径：http://localhost:8080/servletDemo/servlet/ServletDemo

浏览器显示压缩后的数据：

5）：Content-Language：zh-cn  告诉浏览器服务器的语言环境

6）：Content-Type：text/html ; charset=utf-8 告诉浏览器服务器回送数据的内容类型

代码如下：

 public class ServletDemo extends HttpServlet {

     public void doGet(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         doPost(request, response);
     }

     public void doPost(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         // 告诉浏览器显示内容格式
         //response.setContentType("image/jpeg");
         // 或者设置响应头的方式
         response.setHeader("Content-Type", "image/jpeg");
         // 读取图片文件
         InputStream in = this.getServletContext().getResourceAsStream("/1.jpg");
         int len = 0;
         byte[] buf = new byte[1024];
         while ((len = in.read(buf)) > 0) {
             response.getOutputStream().write(buf, 0, len);
         }

     }

 }

查看文件响应头的写法，tomcat服务器到 conf/web.xml

重新部署服务，访问url：http://localhost:8080/servletDemo/servlet/ServletDemo

7）:Last-Modified:服务器告诉浏览器资源最后的修改时间，如果修改时间和缓存一直，那么就使用缓存时间，如果比缓存时间

更新，那么就重新发送数据到浏览器。

8）：Refresh：1；url=http://www.baidu.com  服务器告诉浏览器每隔1秒刷新一次

代码如下：

 public class ServletDemo extends HttpServlet {

     public void doGet(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         doPost(request, response);
     }

     public void doPost(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         Date date = new Date();
         SimpleDateFormat sdf = new SimpleDateFormat("yyyy:MM:dd HH:mm:ss");

         response.setHeader("refresh", "1"); // 让日期时间每隔1秒刷新1次
         response.getOutputStream().write(sdf.format(date).getBytes());
     }

 }

refresh请求头还可以实现定时重定向页面的作用，例如注册页面注册成功后跳转到首页：

代码如下：

 public class ServletDemo extends HttpServlet {

     public void doGet(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         doPost(request, response);
     }

     public void doPost(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         String msg = "页面跳转中...";
         response.setHeader("refresh", "5;url='http://www.baidu.com'"); // 让日期时间每隔1秒刷新1次
         response.getOutputStream().write(msg.getBytes());
     }

 }

访问页面5秒后进行页面跳转！！！

9）:  content-disposition :attachment;filename=""  服务器告诉浏览器以下载的方式处理文件

 public class ServletDemo extends HttpServlet {

     public void doGet(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         doPost(request, response);
     }

     public void doPost(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         if ("download".equals(request.getParameter("type"))) {
             response.setHeader("content-disposition",
                     "attachment;filename=1.jpg");
             InputStream in = this.getServletContext().getResourceAsStream(
                     "/1.jpg");
             OutputStream out = response.getOutputStream();
             int len = 0;
             byte[] buf = new byte[1024];
             while ((len = in.read(buf)) > 0) {
                 out.write(buf, 0, len);
             }
             out.flush();
             out.close();
             in.close();
         } else {
             response.setCharacterEncoding("utf-8");
             response.setContentType("text/html");
             PrintWriter pw = response.getWriter();
             pw.print("<html>");
             pw.print("<head><script type='text/javascript'>"
                     +"function download(){"
                     +"window.open('http://localhost:8080/servletDemo/servlet/ServletDemo?type=download')"
                     +"}"
                     +"</script>"
                     +"</head>");
             /*pw
                     .print("<body><a href='http://localhost:8080/servletDemo/servlet/ServletDemo?type=download'>下载</a></body>");*/
             pw.print("<body><button onclick='download();'>下载</button></body>");
             pw.print("</html>");
             pw.close();

         }

     }
 }

访问url：http://localhost:8080/servletDemo/servlet/ServletDemo

显示“下载”按钮，点击下载按钮下载文件：

10）：Cache-control：no-cache  或者 pragma ： no-cache 或者 expires ：-1都是控制浏览器

是否缓存服务器数据，一般情况下都写上，就不会有浏览器兼容问题。

11）：range 断续下载

如果下载服务器的某个资源，已经下载一半，突然网络断了，下次有网络再下载另一半资源，迅雷下载比较常见：

代码演示：

 /**
  *
  */
 package com.hlcui.socket;

 import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.net.HttpURLConnection;
 import java.net.MalformedURLException;
 import java.net.URL;

 /**
  * @author Administrator 实现断续下载文件
  */
 public class DownloadRange {

     /**
      * @param args
      * @throws IOException
      */
     public static void main(String[] args) throws IOException {
         URL url = new URL("http://localhost:8080/servletDemo/111.txt");
         HttpURLConnection conn = (HttpURLConnection) url.openConnection();

         // 设置断续下载，从第4个字符开始下载
         conn.addRequestProperty("range", "bytes=4-");
         InputStream in = conn.getInputStream();
         FileOutputStream out = new FileOutputStream("F:\\111.txt",true); //追加到内容的末尾
         int len = 0;
         byte[] buf = new byte[1024];
         while ((len = in.read(buf)) > 0) {
             out.write(buf, 0, len);
         }
         in.close();
         out.close();

     }

 }

代码均已经验证！