[javaweb]javaweb中HttpServletResponse實現文件下載，驗證碼和請求重定向功能

• 2022 年 7 月 23 日
• 筆記
• javaweb階段鞏固

HttpServletResponse

web伺服器接受到客戶端的http請求之後，針對這個請求，分別創建一個代表請求的httpServletRequest和代表響應的HttpServletResponse

• 文件下載

  package com.javaweb.servlet;
  
  import javax.servlet.ServletException;
  import javax.servlet.ServletOutputStream;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  import java.io.FileInputStream;
  import java.io.IOException;
  
  /**
   * @author panglili
   * @create 2022-07-19-18:17
   */
  public class Response extends HelloServlet {
      @Override
      protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
          //獲取下載路徑
              String path="C:\\Users\\塔塔\\Pictures\\Camera Roll\\1.jpg";
          //下載的文件名
          String fileName = path.substring(path.lastIndexOf("\\") + 1);
          //設置想辦法讓瀏覽器支援下載需要的
          resp.setHeader("Content-Disposition","attachment;fileName="+fileName);
          //獲取下載文件的輸入流
          FileInputStream stream = new FileInputStream(path);
          //創建緩衝區
          int len=0;
          byte[] buffer = new byte[1024];
          //獲取OutputStream
          ServletOutputStream out = resp.getOutputStream();
          //將文件寫到buffer緩衝區
          while((len=stream.read(buffer))>0){
              out.write(buffer,0,len);
          }
          //關閉流
          stream.close();
          out.close();
      }
  
      @Override
      protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
          doGet(req, resp);
      }
  }
  

• 驗證碼實現

package com.javaweb.servlet;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
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;

/**
 * @author panglili
 * @create 2022-07-19-18:39
 */
public class ImageServlet extends HelloServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //每三秒刷新一次
        resp.setHeader("refresh","3");

        //在記憶體創建一個圖片
        BufferedImage image=new BufferedImage(80,20,BufferedImage.TYPE_INT_BGR);

        //得到圖片
        Graphics2D g=(Graphics2D)image.getGraphics();

        //設置背景顏色
        g.setColor(Color.red);
        g.fillRect(0,0,80,20);
        //給圖片寫數據
        g.setColor(Color.BLACK);
        g.setFont(new Font(null, Font.BOLD,20));
        g.drawString(makeNum(),0,20);

        //告訴瀏覽器這個請求用圖片打開
        resp.setContentType("image/jpeg");
        //網站有快取，不讓存
        resp.setDateHeader("expires",-1);
        resp.setHeader("Cache-Control","no-Cache");
        resp.setHeader("Pragma","no-cache");

        ImageIO.write(image,"jpg",resp.getOutputStream());
    }

    private String makeNum(){
        Random random=new Random();
        String num=random.nextInt(9999999)+"";
        StringBuffer str = new StringBuffer();
        for (int i=0;i<7-num.length();i++){
            str.append("0");
        }
        num=str.toString()+num;
        return num;
    }


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

<servlet>
    <servlet-name>img</servlet-name>
    <servlet-class>com.javaweb.servlet.ImageServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>img</servlet-name>
    <url-pattern>/img</url-pattern>
</servlet-mapping>

• 請求重定向

  package com.javaweb.servlet;
  
  import javax.servlet.ServletException;
  import javax.servlet.http.HttpServlet;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  import java.io.IOException;
  
  /**
   * @author panglili
   * @create 2022-07-19-18:46
   */
  public class Redirect extends HttpServlet {
      @Override
      protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
         resp.sendRedirect("/img");
      }
  
      @Override
      protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
          doGet(req, resp);
      }
  
  
  }
  

  <servlet>
      <servlet-name>redi</servlet-name>
      <servlet-class>com.javaweb.servlet.Redirect</servlet-class>
  </servlet>
  <servlet-mapping>
      <servlet-name>redi</servlet-name>
      <url-pattern>/redi</url-pattern>
  </servlet-mapping>