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
常见应用
1.下载文件
要获取下载文件的路径
下载的文件名是什么
设置想办法让浏览器能够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Output Stream将缓冲区中的数据输出到客户端
package com.lyj.servlet;
import jakarta.servlet.ServletException;
import jakarta.servlet.ServletOutputStream;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
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. 获取下载文件的路径（建议使用相对路径，避免硬编码绝对路径）
String realPath = "C:\\Users\\puton\\IdeaProjects\\MavenClear\\Response2\\src\\main\\resources\\img.png";
System.out.println("下载文件的路径：" + realPath);
// 2. 获取下载的文件名
String filename = realPath.substring(realPath.lastIndexOf("\\") + 1);
// 3. 处理中文文件名（URLEncoder编码）
String encodedFilename = URLEncoder.encode(filename, "UTF-8");
// 4. 设置响应头，支持文件下载
resp.setHeader("Content-Disposition", "attachment; filename=" + encodedFilename);
// 设置内容类型为二进制流（通用格式）
resp.setContentType("application/octet-stream");
// 5. 获取文件输入流和响应输出流
try (FileInputStream in = new FileInputStream(realPath);
ServletOutputStream out = resp.getOutputStream()) {
// 6. 创建缓冲区并写入数据
byte[] buffer = new byte[1024];
int len;
// 读取到的字节数不为-1时继续循环
while ((len = in.read(buffer)) != -1) {
out.write(buffer, 0, len);
}
// 强制刷新输出流
out.flush();
} catch (IOException e) {
e.printStackTrace();
throw new ServletException("文件下载失败", e);
}
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
// POST请求复用GET的处理逻辑
doGet(req, resp);
}
}
2.实现验证码功能
前端实现
后端实现，需要用到Java的图片类，生产一个图片
package com.lyj.servlet;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import javax.imageio.ImageIO;
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 {
//如何让浏览器三秒自动刷新一次
resp.setHeader("refresh","3");
//在内存中创建一张图片
BufferedImage bufferedImage = new BufferedImage(100,100,BufferedImage.TYPE_INT_RGB);
//得到图片
Graphics2D g = (Graphics2D) bufferedImage.getGraphics();//笔
//设置图片的背景颜色
g.setColor(Color.white);
g.fillRect(0,0,100,100);
//给图片写数据
g.setColor(Color.blue);
g.setFont(new Font("Times New Roman",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，不让浏览器缓存
resp.setDateHeader("Expires",-1);
//使用 Cache-Control 头（如 no-cache 或 max-age=0）来控制缓存，因为它比 Expires 更灵活且优先级更高
// // 设置 Cache-Control 头，禁止缓存
resp.setHeader("Cache-Control", "no-cache, no-store, must-revalidate");
// // 兼容 HTTP 1.0 协议
resp.setHeader("Pragma", "no-cache");
//把图片写给浏览器
ImageIO.write(bufferedImage,"JPEG",resp.getOutputStream());
}
///生成随机数
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');
}
String s= sb.toString()+num;
return num;
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
}
}
<?xml version="1.0" encoding="UTF-8"?> <web-app xmlns="https://jakarta.ee/xml/ns/jakartaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="https://jakarta.ee/xml/ns/jakartaee https://jakarta.ee/xml/ns/jakartaee/web-app_6_0.xsd" version="6.0"> <display-name>Welcome to Tomcat</display-name> <description>Welcome to Tomcat</description> <servlet> <servlet-name>filedown</servlet-name> <servlet-class>com.lyj.servlet.FileServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>filedown</servlet-name> <url-pattern>/down</url-pattern> </servlet-mapping> <servlet> <servlet-name>ImageServlet</servlet-name> <servlet-class>com.lyj.servlet.ImageServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>ImageServlet</servlet-name> <url-pattern>/image</url-pattern> </servlet-mapping> </web-app>
3.实现重定向
B一个web资源收到客户端A请求后，B他会通知客户端A去访问另外一个web资源C，这个过程叫做重定向
常见场景：
用户登录
测试
package com.lyj.servlet;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
public class RedirectServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
resp.sendRedirect("/r2/image");
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
}
}
web.xml
<?xml version="1.0" encoding="UTF-8"?> <web-app xmlns="https://jakarta.ee/xml/ns/jakartaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="https://jakarta.ee/xml/ns/jakartaee https://jakarta.ee/xml/ns/jakartaee/web-app_6_0.xsd" version="6.0"> <display-name>Welcome to Tomcat</display-name> <description>Welcome to Tomcat</description> <servlet> <servlet-name>filedown</servlet-name> <servlet-class>com.lyj.servlet.FileServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>filedown</servlet-name> <url-pattern>/down</url-pattern> </servlet-mapping> <servlet> <servlet-name>ImageServlet</servlet-name> <servlet-class>com.lyj.servlet.ImageServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>ImageServlet</servlet-name> <url-pattern>/image</url-pattern> </servlet-mapping> <servlet> <servlet-name>RedirctServlet</servlet-name> <servlet-class>com.lyj.servlet.RedirectServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>RedirctServlet</servlet-name> <url-pattern>/redirect</url-pattern> </servlet-mapping> </web-app>
4.面试题
请你了了重定向和转发的区别？
相同点：页面都会实现跳转
不同点：
请求转发的时候，url不会产生变化 307
重定向的时候，url地址栏会发生变化 302
HttpServletRequest
HttpServletRequest代表客户端的请求，用户通过Http协议访问服务器，HTTP请求中的所有信息会被封装到HttpServletRequest，获得客户端的所有信息
获取前端传递的参数
getParameter(String s) String
getParameterValues(String s) String[]
LoginServlet
package com.lyj.servlet;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.Arrays;
public class LoginServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
resp.setContentType("text/html;charset=UTF-8");
req.setCharacterEncoding("UTF-8");
String username = req.getParameter("username");
String password = req.getParameter("password");
String[] hobbys = req.getParameterValues("hobbys");
System.out.println("=======================");
System.out.println("username: " + username);
System.out.println("password: " + password);
System.out.println("hobbys: " + Arrays.toString(hobbys));
req.getRequestDispatcher("/success.jsp").forward(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
index.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>index</title>
</head>
<body>
<h1>登录</h1>
<div style="text-align: center">
<%-- 以post方式提交表单，提交到login1请求--%>
<form action="${pageContext.request.contextPath}/login" method="post">
用户名<input type="text" name="username">
密码<input type="password" name="password">
爱好
<input type="checkbox" name="hobbys" value="111">111
<input type="checkbox" name="hobbys" value="222">222
<input type="checkbox" name="hobbys" value="333">333
<input type="checkbox" name="hobbys" value="444">444
<br>
<input type="submit">
</form>
</div>
</body>
</html>
success.jsp
<%-- Created by IntelliJ IDEA. User: puton Date: 2025/8/2 Time: 22:07 To change this template use File | Settings | File Templates. --%> <%@ page contentType="text/html;charset=UTF-8" language="java" %> <html> <head> <title>success</title> </head> <body> <h1>SUCCESS</h1> </body> </html>
web.xml
<?xml version="1.0" encoding="UTF-8"?> <web-app xmlns="https://jakarta.ee/xml/ns/jakartaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="https://jakarta.ee/xml/ns/jakartaee https://jakarta.ee/xml/ns/jakartaee/web-app_6_0.xsd" version="6.0"> <display-name>Welcome to Tomcat</display-name> <description>Welcome to Tomcat</description> <servlet> <servlet-name>LoginServlet</servlet-name> <servlet-class>com.lyj.servlet.LoginServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>LoginServlet</servlet-name> <url-pattern>/login</url-pattern> </servlet-mapping> </web-app>
pom.xml
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>org.example</groupId> <artifactId>Request01</artifactId> <packaging>war</packaging> <version>1.0-SNAPSHOT</version> <name>Request01 Maven Webapp</name> <url>http://maven.apache.org</url> <dependencies> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>3.8.1</version> <scope>test</scope> </dependency> <dependency> <groupId>jakarta.servlet</groupId> <artifactId>jakarta.servlet-api</artifactId> <version>6.0.0</version> <scope>compile</scope> </dependency> <!-- https://mvnrepository.com/artifact/javax.servlet.jsp/javax.servlet.jsp-api --> <dependency> <groupId>javax.servlet.jsp</groupId> <artifactId>javax.servlet.jsp-api</artifactId> <version>2.3.3</version> </dependency> </dependencies> <build> <finalName>Request01</finalName> </build> </project>