Http响应response（⽂件下载、验证码）
Http响应response
response：响应
作⽤:  往浏览器写东西
组成部分:  响应⾏响应头响应体
操作响应⾏
格式: 协议/版本状态码状态码说明
状态码:
1xx：已发送请求
2xx：已完成响应
200：正常响应
3xx：还需浏览器进⼀步操作
302：重定向配合响应头:location
304：读缓存
4xx:⽤户操作错误
404:⽤户操作错误.
405：访问的⽅法不存在
5xx：服务器错误
500：内部异常
常⽤⽅法:
setStatus(int状态码)：针对于 1xx  2xx  3xx
了解 :sendError(int状态码)：针对于 4xx和5xx
操作响应头
  格式:  key:value(value可以是多个值)
常⽤的⽅法:
setHeader(String key,String value)：设置字符串形式的响应头
了解:setIntHeader(String key,int value)：设值整形的响应头
了解:setDateHeader(String key,long value)：设值时间的响应头
addHeader(String key,String value)：添加字符串形式的响应头之前设置过则追加，若没有设置过则设置
了解:addIntHeader(String key,int value)：添加整形的响应头
了解:addDateHeader(String key,long value)：添加时间的响应头
常⽤的响应头:
location：重定向
refresh：定时刷新
content-type：设置⽂件的mime类型，设置响应流的编码及告诉浏览器⽤什么编码打开
content-disposition:⽂件下载
重定向:
⽅式1:
★response.sendRedirect("/day10/loc2");
⽅式2:
response.setStatus(302);
respooen.setHeader("location","/day10/loc2");
案例1：请求重定向
<servlet>
<servlet-name>SHServlet1</servlet-name>
<servlet-class>quest_response.SHServlet1</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>SHServlet1</servlet-name>
<url-pattern>/servlet1</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>SHServlet2</servlet-name>
<servlet-class>quest_response.SHServlet2</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>SHServlet2</servlet-name>
<url-pattern>/servlet2</url-pattern>
</servlet-mapping>
SHServlet1.java源码
package quest_response;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class SHServlet1 extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //重定向⽅式⼀
//1.设置状态码
response.setStatus(302);
//2.设置响应头
//response.setHeader("location", "/Servlet/servlet2");
//重定向⽅式⼆：设置响应头
response.sendRedirect("/Servlet/servlet2");
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        doGet(request, response);
}
}
SHServlet2.java源码：
package quest_response;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class SHServlet2 extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        response.setContentType("text/html;charset=utf-8");
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        doGet(request, response);
}
}
定时刷新:
⽅案1：设置头 refresh
respooen.setHeader("refresh","秒数;url=跳转的路径");
⽅案2:http的meta标签
<meta http-equiv="refresh" content="3;url=/day10/refresh2.html">
package com.hjh.servlet;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.hjh.domain.User;
import com.hjh.service.UserService;
public class LoginServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //1.设置编码
response.setContentType("text/html;charset=utf-8");
//2.接收⽤户名和密码
String username = Parameter("username");
String password = Parameter("password");
//3.调⽤UserService的login（username，password），返回⼀个user对象
User user  = new UserService().login(username,password);
//4.判断user是否为空
if(user==null) {
//user为空
//优化，定时跳转
response.setHeader("refresh","3;url=/Servlet/login.html");
}else {
//user为不为空
}
}
}
案例⼆：
refresh1.html：
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<!--
http-equiv：响应头
content：响应体
-->
<meta  http-equiv="refresh" content="3;url=/Servlet/refresh2.html" >
<title>注册页⾯</title>
</head>
<body>
注册成功，<span id="sid">5</span>秒之后跳转到登录页⾯
</body>
<script type="text/javascript">
onload=function(){
//设置定时器
setInterval(changeS,1000);
}
i=5;
function changeS(){
/
/1.获取元素
var obj = ElementById("sid");
//2.操作元素的标签体
obj.innerHTML=--i;
}
</script>
</html>
refresh2.html:
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>登录页⾯</title>
</head>
<body>
访问前，请先进⾏登录！
</body>
</html>
；
页⾯上时间会⾃减，5秒后页⾯跳转到refresh2.html
操作响应体：页⾯上要展⽰的内容
常⽤⽅法:
Writer getWriter()：字符流
ServletOutputStream getOutputStream() ：字节流
⾃⼰写的东西⽤字符流，其他⼀概⽤字节流.
处理响应中⽂乱码:
⽅式1:★
response.setContentType("text/html;charset=utf-8");
⽅式2：理解
response.setHeader("content-type", "text/html;charset=utf-8");
注意:
两个流互斥。当响应完成之后，服务器会判断⼀下流是否已经关闭，若没有关闭，服务器会帮我们关闭.(底层使⽤的缓冲流)
案例：
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="/2001/XMLSchema-instance" xmlns="/xml/ns/javaee" xsi:schemaLocation="/xml/ns/javaee /xml/ns/javaee  <servlet>
<servlet-name>PrintServlet</servlet-name>
<servlet-class>com.hjh.servlet.PrintServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>PrintServlet</servlet-name>
<url-pattern>/print</url-pattern>
</servlet-mapping>
</web-app>
PrintServlet.java源码如下：
package com.hjh.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 PrintServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//处理响应的中⽂乱码
response.setContentType("text/html;charset=utf-8");
//打印表格
//获取字符流
PrintWriter writer = Writer();
writer.print("<table border='1'><tr>");
writer.print("<td>⽤户名：</td>");
writer.print("<td>tom</td></tr>");
writer.print("<tr><td>密码：</td>");
writer.print("<td>123</td>");
writer.print("</tr></table>");
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        doGet(request, response);
}
}
在没有红⾊标注的这段代码时，启动项⽬访问，浏览器中显⽰的是以下数据：
在加上红⾊标注的代码时，启动项⽬访问，浏览器中显⽰的是以下数据：
⽂件下载：
下载⽅式:
1.超链接下载
<a href="/day10/">下载 </a>
若浏览器能解析该资源的mime类型，则打开；若不能接下则下载;
2.编码下载通过servlet完成
<a href="/day10/download?">下载 </a>
a.设置⽂件的mime类型
String MimeType(⽂件名)
response.setContentType(mimeType);
b.设置下载头信息 content-disposition
response.setHeader("content-disposition", "attachment;filename="+⽂件名称);
c.提供流
1.超链接下载⽂件：
download.html内容如下：
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>超链接⽂件下载</title>
</head>
<body>
<a href='/Servlet/file/1.html'>1.html</a>
<a href='/Servlet/'&</a>
<a href='/Servlet/file/3.docx'>3.docx</a>
</body>
</html>
启动项⽬，浏览器中输⼊url回车，页⾯显⽰如下：
点击1.html这个超链接，浏览器能够识别html的⽂件类型，所以将1.html⽂件内容显⽰在浏览器中，页⾯显⽰如下：
点击2.txt这个超链接，浏览器能够识别txt的⽂件类型，所以将2.txt⽂件内容显⽰在浏览器中，页⾯显⽰如下：
点击3.docx这个超链接，浏览器⽆法识别docx的⽂件类型，浏览器中弹出选择下载保存位置，页⾯显⽰如下：
案例⼆：编码下载，通过servlet实现
download2.html：
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>超链接⽂件下载</title>
</head>
<body>
<a href="/Servlet/download?name=1.html">1.html</a><br/>
<a href="/Servlet/download?"&</a><br/>
<a href="/Servlet/download?name=3.docx">3.docx</a><br/>java浏览器下载
</body>
</html>
DownloadServlet.java源码：
package com.hjh.servlet;
import java.io.IOException;
import java.io.InputStream;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class DownloadServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //获取当前下载⽂件的⽂件名
String fileName = Parameter("name");
System.out.println(fileName);
//获取上下⽂
ServletContext context = ServletContext();
//⽂件下载
//1.⾸先获取⽂件的mime类型，并设置其类型
String mimeType = MimeType(fileName);
response.setContentType(mimeType);
//2.设置下载的头信息
response.setHeader("content-disposition", "attchment;filename="+fileName);
//3.对拷流
//3.1获取输⼊流
InputStream is = ResourceAsStream("/file/"+fileName);
//3.2获取输出流
ServletOutputStream os = OutputStream();
int len = -1;
byte[] b = new byte[1024];
while((ad(b))!=-1) {
os.write(b, 0,len);
}
/
/关闭流
os.close();
is.close();
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        doGet(request, response);
}
}
<servlet>
<servlet-name>DownloadServlet</servlet-name>
<servlet-class>com.hjh.servlet.DownloadServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>DownloadServlet</servlet-name>
<url-pattern>/download</url-pattern>
</servlet-mapping>
启动项⽬，浏览器中输⼊url，回车，页⾯显⽰如下：
点击1.html、2.txt、3.docx超链接，浏览器中弹出选择下载保存位置，页⾯显⽰如下：
⽂件下载优化：解决⽂件名带中⽂
  download.html
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>超链接⽂件下载</title>
</head>
<body>
<a href='/Servlet/file/1a.html'>1a.html</a>
<a href='/Servlet/'&</a>
<a href='/Servlet/file/3答案.docx'>3答案.docx</a>
</body>
</html>
  ⼯具类DownLoadUtils.java源码：
package com.hjh.util;
import java.io.UnsupportedEncodingException;