response应用

一、response下载文件

1.新建FileServlet类

// 文件下载测试
public class FileServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 1.获取要下载的文件路径 直接写死的笨办法
        String realPath = "E:\\untitled\\servlet\\response\\target\\classes\\HeaderImg.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);
        System.out.println("下载文件的名字：" + FileName);
        // 3.设置让浏览器能够支持下载需要的东西 Content-disposition URLEncoder.encode解决中文乱码问题
        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OutputStram将缓冲区中的数据输出到客户端
        while ((len = in.read(buffer)) > 0){
            out.write(buffer,0,len);
        }
        in.close();
        out.close();
    }
}

2.配置servlet映射

<?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">
    <servlet>
        <servlet-name>filedown</servlet-name>
        <servlet-class>com.wuxin.servlet.FileServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>filedown</servlet-name>
        <url-pattern>/down</url-pattern>
    </servlet-mapping>
</web-app>

二、response实现验证码

1.新建ImageServlet类

public class ImageServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 如何让浏览器3秒刷新一次
        resp.setHeader("refresh","3");
        // 在内存中创建一张图片
        BufferedImage Image = new BufferedImage(80,80,BufferedImage.TYPE_INT_RGB);
        // 得到图片
        Graphics2D g = (Graphics2D) Image.getGraphics();
        // 设置图片背景颜色
        g.setColor(Color.white);    // 设置画笔颜色
        g.fillRect(0,0,80,20);
        // 给图片写数据
        g.setColor(Color.blue);     // 设置画笔颜色
        g.setFont(new Font(null,Font.BOLD,20));    // 设置画笔字体
        g.drawString(makeNum(),0,20);   // 画随机数字

        // 告诉浏览器，这个请求用图片的方式打开 jpeg或者png
        resp.setContentType("image/jpeg");

        // 网站存在缓存，不让浏览器缓存 早些年的写法，由于电脑配置越来越高，可以不写
        resp.setDateHeader("expires",-1);
        resp.setHeader("Cache-Control","no-cache");
        resp.setHeader("Pragme","no-cache");

        // 把图片写给浏览器
        ImageIO.write(Image,"jpeg",resp.getOutputStream());
    }
 
    // 生成随机数
    private String makeNum(){
        Random random = new Random();
        String num = random.nextInt(9999) + "";
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < 4 - num.length(); i++) {
            sb.append("0");
        }
        String s = sb.toString() + num;
        return num;
    }
}

2.配置web.xml映射

<?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">
    <servlet>
        <servlet-name>filedown</servlet-name>
        <servlet-class>com.wuxin.servlet.FileServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>filedown</servlet-name>
        <url-pattern>/down</url-pattern>
    </servlet-mapping>


    <servlet>
        <servlet-name>FileDown</servlet-name>
        <servlet-class>com.wuxin.servlet.TestFileDownLoad</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>FileDown</servlet-name>
        <url-pattern>/Load</url-pattern>
    </servlet-mapping>


    <servlet>
        <servlet-name>ImageServlet</servlet-name>
        <servlet-class>com.wuxin.servlet.ImageServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>ImageServlet</servlet-name>
        <url-pattern>/img</url-pattern>
    </servlet-mapping>
</web-app>

三、response实现重定向

resp.sendRedirect("/r/img");