JavaWeb 檔案下載案例 (response)
阿新 • • 發佈：2021-02-05
學習資歷：黑馬JAVA2019版
自制簡易驗證碼邏輯：
package cn.web.servlet;
import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet. 下載servlet:
注意兩點：
1.html中的超鏈填寫servlet的虛擬路徑
2.html中超鏈引數不能有空格
package cn.web.download;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.FileInputStream;
import java.io.IOException;
@WebServlet("/downLoadServlet")
public class DownLoadServlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//1.獲取請求引數，檔名稱
String filename = request.getParameter("filename");
//2.使用位元組輸入流載入檔案進記憶體
//2.1找到檔案伺服器路徑
ServletContext servletContext = this.getServletContext();
String realpath = servletContext.getRealPath("/img/"+filename); //初始路徑在web處
//2.2用位元組輸入流關聯(生成輸入流)
FileInputStream fis = new FileInputStream(realpath);
//3.設定response響應頭
//3.1設定響應頭型別,context-type 告訴瀏覽器檔案型別
String mimeType = servletContext.getMimeType(filename);
response.setHeader("content-type",mimeType);
//3.2設定響應頭開啟方式:content-disposition 告訴瀏覽器開啟方式
response.setHeader("content-disposition","attachment;filename=" + filename); //以附件形式開啟
//4.將輸入流的資料寫出到輸出流中
ServletOutputStream sos = response.getOutputStream();
byte [] buff = new byte[1024 * 8]; //快取區
int len = 0;
while((len = fis.read(buff)) != -1) //讀到buff快取區中，若不等於-1則沒讀完
{
sos.write(buff,0,len);
}
fis.close();//關閉輸入流
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doPost(request,response);
}
}
HTML:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
//這樣的超鏈點開來是直接開啟的，並且路徑固定，一旦要改非常麻煩
<a href="/download/488.png">圖片1</a>
<hr>
//裡面servlet地址填虛擬路徑
//注意問號後面filname=xxx不能有空格，不然完全讀不到引數
<a href="/day15/downLoadServlet?filename=640.png">圖片1</a>
<a href="/day15/downLoadServlet?filename=ex1.png">圖片2</a>
</body>
</html>