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：

 1 public class ServletDemo extends HttpServlet {
 2 
 3     public void doGet(HttpServletRequest request, HttpServletResponse response)
 4             throws ServletException, IOException {
 5         doPost(request, response);
 6     }
 7 
 8     public void doPost(HttpServletRequest request, HttpServletResponse response)
 9             throws ServletException, IOException {
10         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
11         response.setHeader("location", "/servletDemo/1.html");
12 
13     }
14 
15 }

web.xml配置：

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <web-app version="2.5" 
 3     xmlns="http://java.sun.com/xml/ns/javaee" 
 4     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
 5     xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
 6     http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
 7   <servlet>
 8     <description>This is the description of my J2EE component</description>
 9     <display-name>This is the display name of my J2EE component</display-name>
10     <servlet-name>ServletDemo</servlet-name>
11     <servlet-class>com.hlcui.servlet.ServletDemo</servlet-class>
12   </servlet>
13 
14   <servlet-mapping>
15     <servlet-name>ServletDemo</servlet-name>
16     <url-pattern>/servlet/ServletDemo</url-pattern>
17   </servlet-mapping>
18  
19   <welcome-file-list>
20     <welcome-file>index.jsp</welcome-file>
21   </welcome-file-list>
22 </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：

 1 public class ServletDemo extends HttpServlet {
 2 
 3     public void doGet(HttpServletRequest request, HttpServletResponse response)
 4             throws ServletException, IOException {
 5         doPost(request, response);
 6     }
 7 
 8     public void doPost(HttpServletRequest request, HttpServletResponse response)
 9             throws ServletException, IOException {
10         String content = "wertyuiopdfghjkl;dfghjklertyuiodfghjkcvbnmcvb"
11                 + "wertyuiopdfghjkl;dfghjklertyuiodfghjkcvbnmcvbtyuiopvbhnjk"
12                 + "wertyuiopdfghjkl;dfghjklertyuiodfghjkcvbnmcvbtyuiopvbhnjk"
13                 + "wertyuiopdfghjkl;dfghjklertyuiodfghjkcvbnmcvbtyuiopvbhnjk"
14                 + "wertyuiopdfghjkl;dfghjklertyuiodfghjkcvbnmcvbtyuiopvbhnjk"
15                 + "wertyuiopdfghjkl;dfghjklertyuiodfghjkcvbnmcvbtyuiopvbhnjk"
16                 + "wertyuiopdfghjkl;dfghjklertyuiodfghjkcvbnmcvbtyuiopvbhnjk";
17 
18         System.out.println("压缩前数据大小：" + content.getBytes().length);
19         ByteArrayOutputStream array = new ByteArrayOutputStream();
20         GZIPOutputStream gzip = new GZIPOutputStream(array);
21         gzip.write(content.getBytes()); // 将内容进行压缩
22         gzip.close();
23 
24         System.out.println("压缩后数据大小：" + array.size());
25         // 告诉浏览器数据压缩格式以及大小
26         response.setHeader("Content-Encoding", "gzip");
27         response.setHeader("Content-Length", array.size() + "");
28         // 将内容写到浏览器
29         response.getOutputStream().write(array.toByteArray());
30 
31     }
32 
33 }

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：

 1 public class ServletDemo extends HttpServlet {
 2 
 3     public void doGet(HttpServletRequest request, HttpServletResponse response)
 4             throws ServletException, IOException {
 5         doPost(request, response);
 6     }
 7 
 8     public void doPost(HttpServletRequest request, HttpServletResponse response)
 9             throws ServletException, IOException {
10         // 告诉浏览器显示内容格式
11         //response.setContentType("image/jpeg");
12         // 或者设置响应头的方式
13         response.setHeader("Content-Type", "image/jpeg");
14         // 读取图片文件
15         InputStream in = this.getServletContext().getResourceAsStream("/1.jpg");
16         int len = 0;
17         byte[] buf = new byte[1024];
18         while ((len = in.read(buf)) > 0) {
19             response.getOutputStream().write(buf, 0, len);
20         }
21 
22     }
23 
24 }

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：

 1 public class ServletDemo extends HttpServlet {
 2 
 3     public void doGet(HttpServletRequest request, HttpServletResponse response)
 4             throws ServletException, IOException {
 5         doPost(request, response);
 6     }
 7 
 8     public void doPost(HttpServletRequest request, HttpServletResponse response)
 9             throws ServletException, IOException {
10         Date date = new Date();
11         SimpleDateFormat sdf = new SimpleDateFormat("yyyy:MM:dd HH:mm:ss");
12 
13         response.setHeader("refresh", "1"); // 让日期时间每隔1秒刷新1次
14         response.getOutputStream().write(sdf.format(date).getBytes());
15     }
16 
17 }

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：

 1 public class ServletDemo extends HttpServlet {
 2 
 3     public void doGet(HttpServletRequest request, HttpServletResponse response)
 4             throws ServletException, IOException {
 5         doPost(request, response);
 6     }
 7 
 8     public void doPost(HttpServletRequest request, HttpServletResponse response)
 9             throws ServletException, IOException {
10         String msg = "页面跳转中...";
11         response.setHeader("refresh", "5;url='http://www.baidu.com'"); // 让日期时间每隔1秒刷新1次
12         response.getOutputStream().write(msg.getBytes());
13     }
14 
15 }

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

 1 public class ServletDemo extends HttpServlet {
 2 
 3     public void doGet(HttpServletRequest request, HttpServletResponse response)
 4             throws ServletException, IOException {
 5         doPost(request, response);
 6     }
 7 
 8     public void doPost(HttpServletRequest request, HttpServletResponse response)
 9             throws ServletException, IOException {
10         if ("download".equals(request.getParameter("type"))) {
11             response.setHeader("content-disposition",
12                     "attachment;filename=1.jpg");
13             InputStream in = this.getServletContext().getResourceAsStream(
14                     "/1.jpg");
15             OutputStream out = response.getOutputStream();
16             int len = 0;
17             byte[] buf = new byte[1024];
18             while ((len = in.read(buf)) > 0) {
19                 out.write(buf, 0, len);
20             }
21             out.flush();
22             out.close();
23             in.close();
24         } else {
25             response.setCharacterEncoding("utf-8");
26             response.setContentType("text/html");
27             PrintWriter pw = response.getWriter();
28             pw.print("<html>");
29             pw.print("<head><script type='text/javascript'>" 
30                     +"function download(){" 
31                     +"window.open('http://localhost:8080/servletDemo/servlet/ServletDemo?type=download')"
32                     +"}"
33                     +"</script>"
34                     +"</head>");
35             /*pw
36                     .print("<body><a href='http://localhost:8080/servletDemo/servlet/ServletDemo?type=download'>下载</a></body>");*/
37             pw.print("<body><button onclick='download();'>下载</button></body>");
38             pw.print("</html>");
39             pw.close();
40 
41         }
42 
43     }
44 }

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：

 1 /**
 2  * 
 3  */
 4 package com.hlcui.socket;
 5 
 6 import java.io.FileOutputStream;
 7 import java.io.IOException;
 8 import java.io.InputStream;
 9 import java.net.HttpURLConnection;
10 import java.net.MalformedURLException;
11 import java.net.URL;
12 
13 /**
14  * @author Administrator 实现断续下载文件
15  */
16 public class DownloadRange {
17 
18     /**
19      * @param args
20      * @throws IOException
21      */
22     public static void main(String[] args) throws IOException {
23         URL url = new URL("http://localhost:8080/servletDemo/111.txt");
24         HttpURLConnection conn = (HttpURLConnection) url.openConnection();
25 
26         // 设置断续下载，从第4个字符开始下载
27         conn.addRequestProperty("range", "bytes=4-");
28         InputStream in = conn.getInputStream();
29         FileOutputStream out = new FileOutputStream("F:\111.txt",true); //追加到内容的末尾
30         int len = 0;
31         byte[] buf = new byte[1024];
32         while ((len = in.read(buf)) > 0) {
33             out.write(buf, 0, len);
34         }
35         in.close();
36         out.close();
37 
38     }
39 
40 }

代码均已经验证！