Javaweb — response应用

学习了javaweb中的response ，写篇博客记录一下

前言

一、用于下载

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 = "D:\\IdeaProjects\\Javaweblearn\\response\\src\\main\\resource\\1.jpg";
        System.out.println("下载文件的路径为："+realPath);
        //2.下载的文件名是什么(小技巧--截取最后一个字符串+1 -->得到 1.jpg)
        String filename = realPath.substring(realPath.lastIndexOf("\\"+1));
        //3.设置想办法让(Content-Disposition)浏览器能够支持下载我们需要的东西  注意：中文文件名要用URLEncoder.encode编码，否则有肯能会乱码
        resp.setHeader("Content-Disposition","attachment;filename="+ URLEncoder.encode(filename,"utf-8"));
        //4.获取下载文件的输入流
        //D:\IdeaProjects\Javaweblearn\response\src\main\resource\1.jpg
        FileInputStream in = new FileInputStream(realPath);
        //5.创建缓冲区
        int len = 0;
        byte[] buffer = new byte[1024];
        //获取OutputStream对象
        ServletOutputStream out = resp.getOutputStream();
        //7.将FileOutputStream流写入到buffer缓冲区
        while (in.read(buffer)>0){
    
    
            out.write(buffer,0,len);
        }
        in.close();
        out.close();
        //8.使用OutputStream将缓冲区中的数据输出到客户端！

二、验证码生成

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    
        //如何让浏览器五秒刷新一次
        response.setHeader("refresh","3");

        //在内存中创建一个图片
        BufferedImage image = new BufferedImage(80,20,BufferedImage.TYPE_3BYTE_BGR);
        //得到图片
        Graphics2D g = (Graphics2D)image.getGraphics();  //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
        g.setColor(Color.GREEN);
        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
        response.setContentType("image/jpg");

        //网站存在缓存，不让浏览器缓存
        response.setDateHeader("expires",-1);
        response.setHeader("Cache-Control","no-cache");
        response.setHeader("Pragma","no-cache");

        //把图片写给浏览器
        ImageIO.write(image,"jpg",response.getOutputStream());


    }

    private java.lang.String makeNum(){
    
    
        Random random = new Random();
        String num = random.nextInt(999999) + "";
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < 6-num.length(); i++) {
    
    
            sb.append("0");
        }
        num = sb.toString() + num;
        return num;

    }

三、重定向

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    
        String username = request.getParameter("username");
        String password = request.getParameter("password");

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

        response.sendRedirect("/success.jsp");
    }