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JavaWeb学习笔记（狂神版）--- 第七节 HttpServletResponse

点亮自己的那盏灯 2022-01-20 阅读 38
java前端maven后端tomcat

第七节 HttpServletResponse

目录

web服务器收到客户端的http请求，针对这个请求，分别创建一个代表请求的HttpServletResponse对象，代表响应的一个HttpServletRequest

  • 要获取客户端请求过来的参数：找HttpServletRequest
  • 要给客户端响应一些信息：找HttpServletResponse

7.1 方法简单分类

负责向浏览器发送数据的

ServletOutputStream getOutputStream() throws IOException;
PrintWriter getWriter() throws IOException;

负责向浏览器发送响应头的方法

    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;

7.2 下载文件

在这里插入图片描述

创建新的Moudel，在java目录下创建FileServlet类

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //1. 获取下载文件的路径
        String realPath = "C:\\Users\\苗俊杰\\IdeaProjects\\HelloServlet\\response\\target\\classes\\1.png";
        System.out.println("文件下载路径"+realPath);
        //2. 下载的文件名
        String filename = realPath.substring(realPath.lastIndexOf("/")+1);
        //3. 设置想办法让浏览器能够支持我们下载所需要的东西
        resp.setHeader("Content-disposition","attachment;filename="+filename);
        //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OutputStream
        ServletOutputStream outputStream = resp.getOutputStream();
        //7. 将FileOutputStream写入到buffer缓冲区
        while ((len=fileInputStream.read(buffer))!=1){
            outputStream.write(buffer,0,len);
        }
        fileInputStream.close();
        outputStream.close();
        //8. 使用OutputStream将缓冲区中的数据输出到客户端
    }

在web.xml中注册servlet

    <servlet>
        <servlet-name>file</servlet-name>
        <servlet-class>com.mjj.servlet.FileServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>file</servlet-name>
        <url-pattern>/pic</url-pattern>
    </servlet-mapping>

启动测试

7.3 验证码功能

验证码的来源：前端JS，后端Java图片类等

在java目录下创建ImageServlet类

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //如何让浏览器3秒自动刷新一次
        resp.setHeader("refresh","3");
        //在内存中创建图片
        BufferedImage image= new BufferedImage(80,20,BufferedImage.TYPE_INT_RGB);
        //得到图片
        Graphics2D graphics = (Graphics2D) image.getGraphics();
        graphics.setColor(Color.white);
        graphics.fillRect(0,0,80,20);
        //为图片写数据
        graphics.setColor(Color.blue);
        graphics.setFont(new Font(null,Font.BOLD,20));
        graphics.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");
       //把图片写给浏览器
        boolean write = ImageIO.write(image,"jpg",resp.getOutputStream());
    }
    //生成随机数
    private String makeNum(){
        Random random = new Random();
        String s = random.nextInt(99999999)+"";
        StringBuffer sb = new StringBuffer();
        //注意这里，是为了保证验证码是八位数，如果随机生成的数不满八位，则用0填充
        for (int i=0;i<7-s.length();i++){
            sb.append("0");
        }
        s = sb.toString()+s;
        return  s;
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }

在web.xml中注册servlet

    <servlet>
        <servlet-name>image</servlet-name>
        <servlet-class>com.mjj.servlet.ImageServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>image</servlet-name>
        <url-pattern>/image</url-pattern>
    </servlet-mapping>

启动测试

在这里插入图片描述

7.4 实现重定向

在这里插入图片描述

一个web资源收到客户端请求后，它会通知客户端去访问令一个web资源，这个过程就是重定向

常见场景：用户登录

void sendRedirect(String var1) throws IOException;

创建一个RedirectServlet类

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    //resp.setHeader("Location","/r1/image");
    //resp.setStatus(302);
    //可以理解为：sendDedirect就是封装后的setHeader和setStatus
    resp.sendRedirect("/r1/image"); 
}

配置servlet

    <servlet>
        <servlet-name>re</servlet-name>
        <servlet-class>com.mjj.servlet.RedirectServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>re</servlet-name>
        <url-pattern>/re</url-pattern>
    </servlet-mapping>

这个时候访问/re可直接跳转到/image的页面中去

在这里插入图片描述

面试题：重定向与转发的区别

请求转发时，url不会发生改变，请求重定向时会发生改变

在这里插入图片描述

7.5 HttpServletResponse与HttpServletRequest

在pom文件中导入jsp的包

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.11</version>
      <scope>test</scope>
    </dependency>
  <!-- https://mvnrepository.com/artifact/javax.servlet.jsp/javax.servlet.jsp-api -->
  <dependency>
    <groupId>javax.servlet.jsp</groupId>
    <artifactId>javax.servlet.jsp-api</artifactId>
    <version>2.2.1</version>
  </dependency>
  </dependencies>

创建一个Request类

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //处理请求
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        System.out.println(username+":"+password);
        //处理响应,使用重定向
        resp.sendRedirect("/r1/success.jsp");
    }

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

修改jsp文件

index.jsp
<%@ page contentType="text/html;charset=GBK"%>
<html>
<body>
<h2>Hello World!</h2>
<%--z这里action提交的路径，需要寻找到项目的路径--%>
<%--{pageContext.request.contextPath}表示当前的路径--%>
    <form action="${pageContext.request.contextPath}/request" method="get">
        用户名：<input type="text" name="username"><br>
        密码：<input type="password" name="password"><br>
        <input type="submit" value="提交">
    </form>
</body>
</html>
    
success.jsp
<html>
<head>
    <title>Title</title>
</head>
<body>
    <h1>跳转成功</h1>
</body>
</html>

注册servlet

    <servlet>
        <servlet-name>request</servlet-name>
        <servlet-class>com.mjj.servlet.RequestTest</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>request</servlet-name>
        <url-pattern>/request</url-pattern>
    </servlet-mapping>

启动测试

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