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！