Java-web-HttpServletResponse

转载

mob60475702a1ff 2021-08-08 21:35:00

文章标签 JavaWeb学习笔记 java 客户端下载文件 ide 文章分类 代码人生

Java-web-HttpRunner

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,代表响应的一个HttoServletResponse

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

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);

设置响应头

    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);

响应码参量:

    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;

文件下载,

向浏览器输出消息
下载文件
- 要获取下载文件的路径
- 下载的文件名是啥
- 设置想办法让浏览器能够支持下载我们需要的东西
- 获取下载文件的输入流
- 创建缓冲区
- 获取OutputStream对象
- 将FileOutputStream流写入到Buffer缓冲区
- 使用OutputStream将缓冲区中的数据输出到客户端!

package com.xinyudoufuf.servlet;

import sun.net.www.content.image.png;

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.FileInputStream;
import java.io.IOException;
import java.net.URLEncoder;

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 =  "E:\\javaweb\\javaweb-02-servlet\\response\\target\\response\\WEB-INF\\classes\\咸鱼豆腐.png";
        System.out.println("下载文件的路径:" + realpath);
//       2.  下载的文件名是啥
        String filename = realpath.substring(realpath.lastIndexOf("\\") + 2);
//       3. 设置想办法让浏览器能够支持下载我们需要的东西,中文文件名,URLEncoder.encode编码,否则有可能会乱码
        resp.setHeader("Content-Disposition","attachment;filename="+ URLEncoder.encode(filename,"utf-8"));
//       4. 获取下载文件的输入流
        FileInputStream fis = 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将缓冲区中的数据输出到客户端!
        while ((len = fis.read(buffer)) > 0) {
            out.write(buffer,0,len);
        }
        fis.close();
        out.close();

    }

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

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,生产一个图片
验证码

package com.xinyudoufuf.servlet;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

public class ImageServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //如何让浏览器5秒自动刷新一次

        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.createGraphics();
        //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.BLUE);
        g.setFont(new Font(null, Font.BOLD, 20));
        g.drawString(makeNum(),0,20);
        //告诉浏览器，这请求用图片的方法打开
        resp.setContentType("image/jpeg");
        //网站存在缓存,
        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
    protected String makeNum() {
        Random random = new Random();
        String num = random.nextInt(99999999) + "";
        StringBuffer sb  = new StringBuffer();
        for (int i = 0; i < 7 - num.length(); i++) {
            sb.append("0");
        }
        String s = sb.toString() + num;
        return num;
    }

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

实现重定向

Java-web-HttpServletResponse_java
一个web资源收到客户端请求后，他会通知客户端去访问另外一个web资源C，这个过程叫重定向
常见场景

用户登录

 void sendRedirect(String var1) throws IOException;

   @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        /*
        resp.setHeader("Location","/r1/aa");
        resp.setStatus(HttpServletResponse.SC_MOVED_TEMPORARILY);
        * */

        resp.sendRedirect("/r1/aa"); //重定向
    }

重定向和转发的区别
相同点