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Servlet案例下载文件，图片验证码

news 来源：原创 2025/6/9 15:59:54

Servlet案例（下载文件，图片验证码）

实现图片下载，响应到浏览器中去（

设置响应的附件名
response.setHeader("Content-Disposition", "attachment;filename="+ UUID.randomUUID().toString()+".png");

）

//TODO:实现文件的下载操作
@WebServlet("/servlet5")
public class MyServlet5 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    //    TODO:设置字符编码为UTF-8
        response.setCharacterEncoding("UTF-8");
    //    TODO:设置响应头，告诉浏览器，使用什么字符集显示
        response.setContentType("text/html;charset=UTF-8");
        //TODO:设置响应的附件名
        response.setHeader("Content-Disposition", "attachment;filename="+ UUID.randomUUID().toString()+".png");
        //TODO:读取文件内容
        FileInputStream fileInputStream = new FileInputStream("D:\\桌面\\课程\\workspace\\web_02\\src\\main\\webapp\\1.png");
        byte[] bytes = new byte[1024];
        int len = 0;
        while ((len = fileInputStream.read(bytes)) != -1) {
            //TODO:将文件内容写入到响应体中
            response.getOutputStream().write(bytes, 0, len);
        }
        fileInputStream.close();

    }

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

图片验证码（通过调用Hutool工具类）

@WebServlet("/servlet6")
public class MyServlet6 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    //    TODO:实现验证码的功能
        // 自定义纯数字的验证码（随机4位数字，可重复）
        RandomGenerator randomGenerator = new RandomGenerator("0123456789", 4);
        LineCaptcha lineCaptcha = CaptchaUtil.createLineCaptcha(200, 100);
        lineCaptcha.setGenerator(randomGenerator);
        // 重新生成code
        lineCaptcha.createCode();
        // 输出图片流
        lineCaptcha.write(response.getOutputStream());
    }

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

通过html展示对应的验证码（<img id="codeImg" src="/web_02/servlet6" alt="图片验证码" onclick="changeCode()">）

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>图片验证码</title>
    <script>
        function changeCode(){
            let img= document.getElementById("codeImg");
            // 在重新设置src的时候，一定要加上时间戳，否则图片不会更新
            img.src="/web_02/servlet6"+"?"+new Date();
            // img.src="/web_02/servlet6";
        }
    </script>
</head>
<body>
    <form action="" method="post">
          用户名<input type="text" name="username"/>
          密码<input type="password" name="password"/>
          验证码<input type="text" name="code">
<!--        TODO:注意在设置对应的src地址的时候要把工件的根目录加上   -->
          <img id="codeImg" src="/web_02/servlet6" alt="图片验证码" onclick="changeCode()">
          </input>
    </form>
</body>
</html>