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
web.xml文件配置
<servlet>
<servlet-name>SHServlet1</servlet-name>
<servlet-class>com.hjh.request_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>com.hjh.request_response.SHServlet2</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>SHServlet2</servlet-name>
<url-pattern>/servlet2</url-pattern>
</servlet-mapping>
SHServlet1.java源码
package com.hjh.request_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 com.hjh.request_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");
response.getWriter().print("跳转到这里啦，哈哈哈");
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}
项目运行，在浏览器中输入“http://localhost:8080/Servlet/servlet1”，回车，url变为“http://localhost:8080/Servlet/servlet2”，浏览网页输出为：“跳转到这里啦，哈哈哈”
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">
案例参见servlet博文：https://www.cnblogs.com/hejh/p/10942445.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 = request.getParameter("username");
String password = request.getParameter("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
response.getWriter().print("用户名和密码不匹配,3秒后跳转");
//优化，定时跳转
response.setHeader("refresh","3;url=/Servlet/login.html");
}else {
//user为不为空
response.getWriter().print(user.getUsername()+"：欢迎回来");
}
}
}
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 = document.getElementById("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>
启动项目，在浏览器中输入“http://localhost:8080/Servlet/refresh1.html”，回车，页面显示显示：
；
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：
web.xml配置信息如下：
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
<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 = response.getWriter();
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/download/day10.txt">下载 day10.txt</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?name=day10.txt">下载 day10.txt</a>
a.设置文件的mime类型
String mimeType=context.getMimeType(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
response.getOutputStream();
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/file/2.txt'>2.txt</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?name=2.txt">2.txt</a><br/>
<a href="/Servlet/download?name=3.docx">3.docx</a><br/>
</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 = request.getParameter("name");
System.out.println(fileName);
//获取上下文
ServletContext context = this.getServletContext();
//文件下载
//1.首先获取文件的mime类型,并设置其类型
String mimeType = context.getMimeType(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 = context.getResourceAsStream("/file/"+fileName);
//3.2获取输出流
ServletOutputStream os = response.getOutputStream();
int len = -1;
byte[] b = new byte[1024];
while((len=is.read(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);
}
}
web.xml配置：
<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/file/2.txt'>2.txt</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;
import java.net.URLEncoder;
import sun.misc.BASE64Encoder;
public class DownLoadUtils {
public static String getName(String agent, String filename) throws UnsupportedEncodingException {
if (agent.contains("MSIE")) {
// IE浏览器
filename = URLEncoder.encode(filename, "utf-8");
filename = filename.replace("+", " ");
} else if (agent.contains("Firefox")) {
// 火狐浏览器
BASE64Encoder base64Encoder = new BASE64Encoder();
filename = "=?utf-8?B?" + base64Encoder.encode(filename.getBytes("utf-8")) + "?=";
} else {
// 其它浏览器
filename = URLEncoder.encode(filename, "utf-8");
}
return filename;
}
}
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;
import org.apache.commons.io.IOUtils;
import com.hjh.util.DownLoadUtils;
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 = request.getParameter("name");
//System.out.println(fileName);
//解决文件下载文件名带中文问题，方式1
fileName = new String(fileName.getBytes("iso8859-1"),"utf-8");
//获取上下文
ServletContext context = this.getServletContext();
//文件下载
//1.首先获取文件的mime类型,并设置其类型
String mimeType = context.getMimeType(fileName);
response.setContentType(mimeType);
//2.设置下载的头信息
response.setHeader("content-disposition", "attachment;filename="+fileName);
//通过工具类编码；解决文件下载文件名带中文问题，方式2
//String filename = DownLoadUtils.getName(request.getHeader("user-agent"), fileName);
//response.setHeader("content-disposition", "attachment;filename="+filename);
//3.对拷流
//3.1获取输入流
InputStream is = context.getResourceAsStream("/file/"+fileName);//方式2，fileName应改为filename
//3.2获取输出流
ServletOutputStream os = response.getOutputStream();
// int len = -1;
// byte[] b = new byte[1024];
// while((len=is.read(b))!=-1) {
// os.write(b, 0,len);
// }
IOUtils.copy(is, os);
//关闭流
os.close();
is.close();
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}
代码优化：引入commons-io-1.4.jar包
在代码中以下面红色部分代码替代黄色部分代码：
IOUtils.copy(is, os);
代替
int len = -1;
byte[] b = new byte[1024];
while((len=is.read(b))!=-1) {
os.write(b, 0,len);
}
案例：验证码
web.xml配置：
<servlet>
<servlet-name>CodeServlet</servlet-name>
<servlet-class>com.hjh.servlet.CodeServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>CodeServlet</servlet-name>
<url-pattern>/code</url-pattern>
</servlet-mapping>
code.html:
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>验证码</title>
</head>
<body>
<img alt="验证码" src="/Servlet/code" title="看不清，换一张" onclick="changeImg(this)">
</body>
<script type="text/javascript">
function changeImg(obj){
//操作src属性
obj.src="/Servlet/code?i="+Math.random();
}
</script>
</html>
CodeServlet.java源码：
package com.hjh.servlet;
import javax.servlet.http.HttpServlet;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;
import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class CodeServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
// 使用java图形界面技术绘制一张图片
int charNum = 4;
int width = 30 * 4;
int height = 30;
// 1. 创建一张内存图片
BufferedImage bufferedImage = new BufferedImage(width, height,
BufferedImage.TYPE_INT_RGB);
// 2.获得绘图对象
Graphics graphics = bufferedImage.getGraphics();
// 3、绘制背景颜色
graphics.setColor(Color.YELLOW);
graphics.fillRect(0, 0, width, height);
// 4、绘制图片边框
graphics.setColor(Color.BLUE);
graphics.drawRect(0, 0, width - 1, height - 1);
// 5、输出验证码内容
graphics.setColor(Color.RED);
graphics.setFont(new Font("宋体", Font.BOLD, 20));
// 随机输出4个字符
Graphics2D graphics2d = (Graphics2D) graphics;
String s = "ABCDEFGHGKLMNPQRSTUVWXYZ23456789";
Random random = new Random();
//session中要用到
String msg="";
int x = 5;
for (int i = 0; i < 4; i++) {
int index = random.nextInt(32);
String content = String.valueOf(s.charAt(index));
msg+=content;
double theta = random.nextInt(45) * Math.PI / 180;
//让字体扭曲
graphics2d.rotate(theta, x, 18);
graphics2d.drawString(content, x, 18);
graphics2d.rotate(-theta, x, 18);
x += 30;
}
// 6、绘制干扰线
graphics.setColor(Color.GRAY);
for (int i = 0; i < 5; i++) {
int x1 = random.nextInt(width);
int x2 = random.nextInt(width);
int y1 = random.nextInt(height);
int y2 = random.nextInt(height);
graphics.drawLine(x1, y1, x2, y2);
}
// 释放资源
graphics.dispose();
// 图片输出 ImageIO
ImageIO.write(bufferedImage, "jpg", response.getOutputStream());
}
public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
doGet(request, response);
}
}
启动项目，输入url，回车，页面显示如下，点击二维码区域，二维码刷新：
