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！