web.xml

<?xml version="1.0" encoding="UTF-8"?>
<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">
  <!--注册Servlet-->
  <servlet>
    <servlet-name>file</servlet-name>
    <servlet-class>com.zty.servlet.FileServlet</servlet-class>
  </servlet>
  <!--Servlet的请求路径-->
  <servlet-mapping>
    <servlet-name>file</servlet-name>
    <url-pattern>/down</url-pattern>
  </servlet-mapping>
  <servlet>
    <servlet-name>image</servlet-name>
    <servlet-class>com.zty.servlet.ImageServlet</servlet-class>
  </servlet>
  <!--Servlet的请求路径-->
  <servlet-mapping>
    <servlet-name>image</servlet-name>
    <url-pattern>/img</url-pattern>
  </servlet-mapping>
  <servlet>
    <servlet-name>RedirectServlet</servlet-name>
    <servlet-class>com.zty.servlet.RedirectServlet</servlet-class>
  </servlet>
  <!--Servlet的请求路径-->
  <servlet-mapping>
    <servlet-name>RedirectServlet</servlet-name>
    <url-pattern>/rs</url-pattern>
  </servlet-mapping>
  <servlet>
    <servlet-name>requset</servlet-name>
    <servlet-class>com.zty.servlet.RequestTest</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>requset</servlet-name>
    <url-pattern>/login</url-pattern>
  </servlet-mapping>
</web-app>

index.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<body>
<h2>Hello World!</h2>

<%--这里提交的路径，需要寻找到项目的路径--%>
<%--${pageContext.request.contextPath}代表当前的项目--%>
<form action="${pageContext.request.contextPath}/login" method="get">
    用户名：<input type="text" name="username"> <br>
    密码：<input type="password" name="password"> <br>
    <input type="submit">
</form>
</body>
</html>

pageContext.request.contextPath这里就是提交路径，填完姓名和密码后，它会通过get方式提交到login的Servlet处，我们再看看loginServlet如何处理

RequestTest

package com.zty.servlet;

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.IOException;

public class RequestTest extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //处理请求
        String username = req.getParameter("username");
        String password = req.getParameter("password");

        System.out.println(username+":"+password);

//重定向时候一定要注意，路径问题，否则404；
//        resp.sendRedirect("/success.jsp");
        resp.sendRedirect("success.jsp");
    }

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

这里通过getParameter方法获取姓名和密码，在后台打印出来，然后重定向到success.jsp，注意重定向的url会跳转，我们试一下！

login测试

在这里插入图片描述

说的没错吧！

FileServlet

package com.zty.servlet;

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.FileInputStream;
import java.io.IOException;
import java.net.URLEncoder;

public class FileServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 1. 要获取下载文件的路径
//        String realPath = "C:\\Users\\Irving\\Desktop\\csLearning\\java\\JavaWeb\\javaweb-servlet\\response\\target\\classes\\张天泳.jpg";
        String realPath = Thread.currentThread().getContextClassLoader().getResource("").getPath() + "张天泳.jpg";
//        System.out.println(Thread.currentThread().getContextClassLoader().getResource("").getPath()); // WebContent目录下的文件绝对路径
        System.out.println("下载文件的路径："+realPath);
        // 2. 下载的文件名是啥？
        String fileName = realPath.substring(realPath.lastIndexOf("/") + 1);
        System.out.println(fileName);
        // 3. 设置想办法让浏览器能够支持(Content-Disposition)下载我们需要的东西,中文文件名URLEncoder.encode编码，否则有可能乱码
        resp.setHeader("Content-Disposition","attachment;filename="+ URLEncoder.encode(fileName,"UTF-8"));
        // 4. 获取下载文件的输入流
        FileInputStream in = new FileInputStream(realPath);
        // 5. 创建缓冲区
        int len = 0;
        byte[] buffer = new byte[1024];
        // 6. 获取OutputStream对象
        ServletOutputStream out = resp.getOutputStream();
        // 7. 将FileOutputStream流写入到buffer缓冲区,使用OutputStream将缓冲区中的数据输出到客户端！
        while ((len=in.read(buffer))>0){
            System.out.println(len);
            out.write(buffer,0,len);
        }

        in.close();
        out.close();
    }

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

如果不想写绝对路径的话，Thread.currentThread().getContextClassLoader().getResource(“”).getPath()可以直接定位到target/classes目录
resp要设置setHeader，这里选择content-disposition，选择附件的形式，记得要utf-8解决中文乱码！
来一个FilteInputStream读入文件
来一个buffer将文件流搞到resp.getOutputStream输出流中
注意(len=in.read(buffer))>0的写法，每次取后面的1024长度，相当于一个指针一直后移，直到到达结尾，体现了分片的思想！
最后记录close两个流！

文件下载测试

在这里插入图片描述

我们发现，down并不是一个jsp，他只是一个下载资源的请求，下载完附件后，还是会留在之前的success.jsp

动态图形验证码Servlet

package com.zty.servlet;

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

public class ImageServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //如何让浏览器3秒自动刷新一次；
        resp.setHeader("refresh","2");
        //在内存中创建一个图片
        BufferedImage image = new BufferedImage(100, 20, BufferedImage.TYPE_INT_BGR);
        //得到图片
        Graphics2D g = (Graphics2D) image.getGraphics();
        //设置图片背景颜色
        g.setColor(Color.white);
        g.fillRect(0,0,100,20);
        //给图片写数据
        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/jpeg");
        //网站存在缓存，不然浏览器缓存
        resp.setDateHeader("expires",-1);
        resp.setHeader("Cache-control","no-cache");
        resp.setHeader("Pragma","no-cache");
        //把图片写给浏览器
        ImageIO.setUseCache(false); // 用内存缓存, 若用文件缓存可能会报错cannot create cache file
        ImageIO.write(image, "jpg", resp.getOutputStream());
    }
    //生成随机数
    private String makeNum(){
        // test2
        Random random = new Random();
        String num = random.nextInt(99999999)+"";
        StringBuffer buffer = new StringBuffer();
        for (int i=0;i<=7-num.length();i++){
            buffer.append("0");
        }
        num = buffer.toString() + num;
        return num;
    }

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