毕设准备---请求，响应

HttpServletResponse

web服务器接收到客户端的http请求，针对这个请求，分别创建一个代表请求的HttpServletRequest对象，代表响应的一个HttpServletResponse

• 如果要获取客户端请求过来的参数：找HttpServletRequest
• 如果要给客户端响应一些信息：找HttpServletResponse

负责向浏览器发送数据的方法

ServletOutputStream getOutputStream() throws IOException;
PrintWriter gerWriter() throws IOException;

常见应用

下载文件

    要获取下载文件的路径
    下载的文件名叫啥
    设置想办法让浏览器支持下载我们需要的东西
    获取下载文件的输入流
    创建缓冲区
    获取OutputStream对象
    将FileOutputStream流写入到buffer缓冲区
    使用OutputStream将缓冲区的数据输出到客户端

FileServlet

package com.wyh.servlet;

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.FileInputStream;
import java.io.IOException;
import java.net.URLEncoder;

/**
 * @author WuYongheng
 * @date 2022/8/30
 * @description
 */
public class FileServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //    要获取下载文件的路径
        String realPath = "D:\\code\\Javaweb\\response\\target\\classes\\联系人.xlsx";
        System.out.println("下载文件的路径：" + realPath);
        //    下载的文件名叫啥
        String fileName = realPath.substring(realPath.lastIndexOf("\\") + 1);
        //    设置想办法让浏览器支持下载我们需要的东西
        resp.setHeader("Content-Disposition", "attachment;filename=" + URLEncoder.encode(fileName, "UTF-8"));
        //    获取下载文件的输入流
        FileInputStream in = new FileInputStream(realPath);
        //    创建缓冲区
        int len = 0;
        byte[] buffer = new byte[1024];
        //    获取OutputStream对象
        ServletOutputStream out = resp.getOutputStream();
        //    将FileOutputStream流写入到buffer缓冲区,使用OutputStream将缓冲区的数据输出到客户端
        while ((len = in.read(buffer)) > 0) {
            out.write(buffer, 0, len);
        }
        in.close();
        out.close();
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }

}

注册

<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
                      http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0"
         metadata-complete="true">
    
    <servlet>
        <servlet-name>filedown</servlet-name>
        <servlet-class>com.wyh.servlet.FileServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>filedown</servlet-name>
        <url-pattern>/wyh</url-pattern>
    </servlet-mapping>
</web-app>

效果：

验证码功能

验证怎么来的？

• 前端实现
• 后端实现，需要用到一个java图片类，生产一个图片

ImageServlet

package com.wyh.servlet;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

/**
 * @author WuYongheng
 * @date 2022/8/30
 * @description
 */
public class ImageServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 如何让浏览器5秒自动刷新一次；
        resp.setHeader("refresh", "5");
        // 在内存中创建一张图片
        BufferedImage image = new BufferedImage(80, 20, BufferedImage.TYPE_INT_RGB);
        // 得到图片，这个图片是在内存中
        Graphics2D g = (Graphics2D) image.getGraphics(); // 这是一支笔
        // 设置图片的背景颜色
        g.setColor(Color.white);
        g.fillRect(0, 0, 80, 20);
        // 给图片写数据，画画
        g.setColor(Color.BLUE);
        g.setFont(new Font(null, Font.BOLD, 20));
        g.drawString(makeNum(), 0, 20);
        // 告诉浏览器，这个请求用图片的方式打开
        resp.setContentType("image/png");
        // 网站存在缓存，不让浏览器缓存
        resp.setDateHeader("expries", -1);
        resp.setHeader("Cache-Control", "no-cache");
        resp.setHeader("Pragma", "no-cache");

        // 把图片写给浏览器
        ImageIO.write(image, "png", resp.getOutputStream());
    }

    // 生成随机数，不够添0，保证 7位
    private String makeNum() {
        Random random = new Random();
        String num = random.nextInt(9999999) + "";
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < 7 - num.length(); i++) {
            sb.append("0");
        }
        num = sb.toString() + num;
        return num;
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

注册

    <servlet>
        <servlet-name>image</servlet-name>
        <servlet-class>com.wyh.servlet.ImageServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>image</servlet-name>
        <url-pattern>/image</url-pattern>
    </servlet-mapping>

效果：

右键可以另存为，说明确实是图片

HttpServletRequset

获取前端传递的参数

请求转发

RequestServlet

package com.wyh.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.Arrays;

/**
 * @author WuYongheng
 * @date 2022/8/30
 * @description
 */
public class LoginServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setCharacterEncoding("utf-8");

        String username = req.getParameter("username");
        String password = req.getParameter("password");
        String[] hobbies = req.getParameterValues("hobby");

        System.out.println(username);
        System.out.println(password);
        System.out.println(Arrays.toString(hobbies));

        // 通过请求转发
        req.getRequestDispatcher("/success.jsp").forward(req,resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

注册

<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
                      http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0"
         metadata-complete="true">

    <servlet>
        <servlet-name>LoginServlet</servlet-name>
    <servlet-class>com.wyh.servlet.LoginServlet</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>LoginServlet</servlet-name>
        <url-pattern>/login</url-pattern>
    </servlet-mapping>
</web-app>

模仿写的首页

注意 action = "login"

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%
    String path = request.getContextPath();
    String basePath = request.getScheme() + "://" + request.getServerName() + ":" + request.getServerPort() + path + "/";
%>
<!DOCTYPE html>
<html>
<head>
    <base href="<%=basePath%>">
    <title>登录</title>
</head>
<body>

<div>
    <form action="login" method="post">
        用户名：<input type="text" name="username"> <br>
        密码：<input type="password" name="password"> <br>
        爱好：
        <input type="checkbox" name="hobby" value="抽烟">抽烟
        <input type="checkbox" name="hobby" value="喝酒">喝酒
        <input type="checkbox" name="hobby" value="上网">上网
        <br>
        <input type="submit">
    </form>
</div>

</body>
</html>

效果