TensorFlow 深度学习中文第二版·翻译完成

Posted 2020-12-19 apachecn

6.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对象和一个代表响应的HttpServletResponse对象；

• 如果要获取客户端请求过来的参数：找HttpServletRequest

• 如果要给客户响应一些信息：找HttpServletResponse

1.简单分类

负责向浏览器发送数据的方法

ServletOutputStream getOutputStream() throws IOException;

PrintWriter getWriter() throws IOException;

负责向浏览器发送响应头的方法

void setCharacterEncoding(String var1);

void setContentLength(int var1);

void setContentLengthLong(long var1);

void setContentType(String var1);

void setDateHeader(String var1, long var2);

void addDateHeader(String var1, long var2);

void setHeader(String var1, String var2);

void addHeader(String var1, String var2);

void setIntHeader(String var1, int var2);

void addIntHeader(String var1, int var2);

响应的状态码

int SC_CONTINUE = 100;
int SC_SWITCHING_PROTOCOLS = 101;
int SC_OK = 200;
int SC_CREATED = 201;
int SC_ACCEPTED = 202;
int SC_NON_AUTHORITATIVE_INFORMATION = 203;
int SC_NO_CONTENT = 204;
int SC_RESET_CONTENT = 205;
int SC_PARTIAL_CONTENT = 206;
int SC_MULTIPLE_CHOICES = 300;
int SC_MOVED_PERMANENTLY = 301;
int SC_MOVED_TEMPORARILY = 302;
int SC_FOUND = 302;
int SC_SEE_OTHER = 303;
int SC_NOT_MODIFIED = 304;
int SC_USE_PROXY = 305;
int SC_TEMPORARY_REDIRECT = 307;
int SC_BAD_REQUEST = 400;
int SC_UNAUTHORIZED = 401;
int SC_PAYMENT_REQUIRED = 402;
int SC_FORBIDDEN = 403;
int SC_NOT_FOUND = 404;
int SC_METHOD_NOT_ALLOWED = 405;
int SC_NOT_ACCEPTABLE = 406;
int SC_PROXY_AUTHENTICATION_REQUIRED = 407;
int SC_REQUEST_TIMEOUT = 408;
int SC_CONFLICT = 409;
int SC_GONE = 410;
int SC_LENGTH_REQUIRED = 411;
int SC_PRECONDITION_FAILED = 412;
int SC_REQUEST_ENTITY_TOO_LARGE = 413;
int SC_REQUEST_URI_TOO_LONG = 414;
int SC_UNSUPPORTED_MEDIA_TYPE = 415;
int SC_REQUESTED_RANGE_NOT_SATISFIABLE = 416;
int SC_EXPECTATION_FAILED = 417;
int SC_INTERNAL_SERVER_ERROR = 500;
int SC_NOT_IMPLEMENTED = 501;
int SC_BAD_GATEWAY = 502;
int SC_SERVICE_UNAVAILABLE = 503;
int SC_GATEWAY_TIMEOUT = 504;
int SC_HTTP_VERSION_NOT_SUPPORTED = 505;

2.下载文件

1. 向浏览器输出信息
2. 下载文件
   1. 要获取下载文件的路径
   2. 下载文件名
   3. 设置让浏览器能够支持下载我们需要的东西
   4. 获取下载文件的输出流
   5. 创建缓冲区
   6. 获取OutputStream对象
   7. 将FileOutputStream流写入到buffer缓冲区,使用OutputStream将缓冲区的数据输出到客户端

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //1. 要获取下载文件的路径
        String realPath = "D:\code\javaweb-02-servlet\response\src\main\resources\1.png";
        System.out.println("下载文件的路径：" + realPath);

        //2. 下载文件名
        String fileName = realPath.substring(realPath.lastIndexOf("\") + 1);

        //3. 设置想办法让浏览器能够支持(Content-Disposition)下载我们需要的东西,中文文件名URLEncoder.encode编码，否则有可能乱码
        resp.setHeader("Content-Disposition","attachment;filename="+ URLEncoder.encode(fileName,"utf-8"));

        //4. 获取下载文件的输出流
        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OutputStream将缓冲区的数据输出到客户端

        while ((len = in.read(buffer))!=-1){
            out.write(buffer,0,len);
        }
        in.close();
        out.close();

    }

3.验证码功能

验证怎么来的？

• 前端实现

• 后端实现，需要用到java的图片类，生成一个图片

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //如何让浏览器3秒钟刷新一次
        resp.setHeader("refresh","3");

        //在内存中创建一个图片
        BufferedImage image = new BufferedImage(80, 20, BufferedImage.TYPE_INT_RGB);

        //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.cyan);
        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
        resp.setContentType("image/jpeg");

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

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

    //生成随机数
    private String makeNum(){
        Random random = new Random();
        String num = random.nextInt(9999999) + "";
        StringBuffer sb = new StringBuffer();
        //确保产生的是七位数
        for (int i = 0; i < 7-num.length(); i++) {
            sb.append("0");
        }
        num = sb.toString() + num;
        return num;
    }

4.实现重定向

什么是重定向？

一个web资源收到客户端请求后，会通知客户端去访问另外一个web资源，这个过程叫做重定向

常见场景：

• 用户登录

  void sendRedirect(String var1) throws IOException; 
  

测试：

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.sendRedirect("/re/img");//重定向
    }

面试题：请说说重定向和转发的区别？

相同点：

• 页面都会实现跳转

不同点：

• 请求转发时，url不会发生变化
• 重定向时，url会发生变化

5.简单实现登录重定向

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<body>
<h2>Hello World!</h2>
<%--这里提交的路径，需要寻找到项目的路径--%>
<%--${pageContext.request.contextPath}代表当前的项目--%>
<form action="${pageContext.request.contextPath}/login" method="get">
    用户名：<input type="text" name="username"><br>
    密码：<input type="password" name="password"><br>
    <input type="submit">
</form>
</body>
</html>

public class RedirectDemo extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        System.out.println(username + ":" + password);
        resp.sendRedirect("/re/Success.jsp");
    }

<servlet>
        <servlet-name>Redirect</servlet-name>
        <servlet-class>com.shida.response.RedirectDemo</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>Redirect</servlet-name>
        <url-pattern>/login</url-pattern>
    </servlet-mapping>

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
    <h1>success</h1>
</body>
</html>