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：