Response应用

下载文件

1.创建servlet

public class Response extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //1获取要下载的文件的路径
        String realPath = "E:\\ideaProjects\\servlet1\\servlet02\\src\\main\\resources\\1.jpg";
        //2获取要下载的文件名（截取1.jpg）
        String fileName = realPath.substring(realPath.lastIndexOf("\\")+1);
        //3设置让浏览器支持下载                                           //如果文件名为中文，则需改编码
        resp.setHeader("Content-Disposition","attachment;filename="+ URLEncoder.encode(fileName,"utf-8"));
        //4获取下载文件的输入流
        FileInputStream fileInputStream = new FileInputStream(realPath);
        //5创建缓冲区
        int len = 0;
        byte[] buffer = new byte[1024];
        //6获取输出流
        ServletOutputStream servletOutputStream = resp.getOutputStream();
        //7将输出流写入缓冲区
        while ((len=fileInputStream.read(buffer))>0)
        {
            servletOutputStream.write(buffer,0,len);
        }
        //关闭输入输出流
        fileInputStream.close();
        servletOutputStream.close();
    }

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

2.注册servlet……
3.运行

实现验证码

public class Response2 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {


        //设置浏览器2秒刷新一次（**********注意：写在第一行才有效）
        resp.setIntHeader("Refresh",2);
        //在内存中创建一个图片
        BufferedImage image = new BufferedImage(100, 20,BufferedImage.TYPE_INT_RGB);
        //创建一个画笔
        Graphics2D g = (Graphics2D) image.getGraphics();
        //设置图片背景颜色
        //设置画笔的颜色
        g.setColor(Color.white);
        //整个图片填充为白色
        g.fillRect(0,0,100,20);
        //在图片中画出随机的验证码数据
        g.setColor(Color.red);
        g.setFont(new Font("Default",1,20));
        g.drawString(getNum(),20,20);
        //把图片写入浏览器
        ImageIO.write(image,"jpg",resp.getOutputStream());
        /************************以下是本节学习重点**************************/

        //设置类型
        resp.setContentType("image/jpeg");
        //设置浏览器不缓存
        resp.setHeader("Cache-Control","no-cache");
        resp.setDateHeader("expires",-1);
        resp.setHeader("Pragma","no-cache");

    }

    //生成随机数
    private String getNum(){
        Random random = new Random();
        String num = random.nextInt(99999)+"";
        StringBuffer stringBuffer = new StringBuffer();
        for (int i = 0; i < 5-num.length(); i++) {
            stringBuffer.append(0);
        }
        num = stringBuffer.toString() + num;
        return num;
    }

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

实现重定向

public class Redirect extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            /*  等同于：
            resp.setHeader("Location","/s3/req2");
            resp.setStatus(302);
            */
         resp.sendRedirect("/s3/req2");   
    }

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