Servlet 下载文件

服务器端有以下文件：

首先，建一个download.html页面（在点击下载的时候，将要下载的文件名传递给服务器端）：

 1 <!DOCTYPE html>
 2 <html>
 3 <head>
 4 <meta charset="UTF-8">
 5 <title>Insert title here</title>
 6 </head>
 7 <body>
 8     <h1>文件下载</h1>
 9     <a href="/Zhan_Web_Servlet/filedownload?filename=a.flv">a.flv</a><br>
10     <a href="/Zhan_Web_Servlet/filedownload?filename=a.jpg">a.jpg</a><br>
11     <a href="/Zhan_Web_Servlet/filedownload?filename=a.mp3">a.mp3</a><br>
12     <a href="/Zhan_Web_Servlet/filedownload?filename=a.mp4">a.mp4</a><br>
13     <a href="/Zhan_Web_Servlet/filedownload?filename=a.txt">a.txt</a><br>
14     <a href="/Zhan_Web_Servlet/filedownload?filename=a.zip">a.zip</a>
15 </body>
16 </html>

Servlet配置文件部分：

 1  <servlet>
 2     <description></description>
 3     <display-name>FileDownloadServlet</display-name>
 4     <servlet-name>FileDownloadServlet</servlet-name>
 5     <servlet-class>demo.FileDownloadServlet</servlet-class>
 6   </servlet>
 7   <servlet-mapping>
 8     <servlet-name>FileDownloadServlet</servlet-name>
 9     <url-pattern>/filedownload</url-pattern>
10   </servlet-mapping>

demo包下面的FileDownloadServlet如下：

 1 package demo;
 2 
 3 import java.io.FileInputStream;
 4 import java.io.IOException;
 5 import java.io.InputStream;
 6 
 7 import javax.servlet.ServletException;
 8 import javax.servlet.ServletOutputStream;
 9 import javax.servlet.http.HttpServlet;
10 import javax.servlet.http.HttpServletRequest;
11 import javax.servlet.http.HttpServletResponse;
12 
13 public class FileDownloadServlet extends HttpServlet {
14 
15     public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
16         //获取要下载文件的名称
17         String fileName = request.getParameter("filename");
18         
19         //客户端通过文件的MIME区分下载的文件的类型,所以在服务器端设置文件的MIME类型
20         response.setContentType(this.getServletContext().getMimeType(fileName));
21         //告诉客户端不要直接解析该文件,而是以附件的形式打开(下载)
22         response.setHeader("Content-Disposition", "attachment;filename=" + fileName);
23        
24         //获取要下载文件的绝对路径
25         String realPath = this.getServletContext().getRealPath("download/" + fileName);
26         
27         ServletOutputStream out = response.getOutputStream();
28         InputStream in = new FileInputStream(realPath);
29         int len = 0;
30         byte[] buffer = new byte[1024];
31         while((len = in.read(buffer)) != -1) {
32             out.write(buffer, 0, len);
33         }
34         in.close();
35         out.close();
36     }
37 
38     public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
39         doGet(request, response);
40     }
41 }

启动服务器，访问download.html，界面如下：

点击要下载的文件链接即可下载。