Servlet实现web站点文件下载功能示例

　　前段时间事情比较多，导致二月份没有记录自己的学习情况。最近接触了servlet，参考韩老师的教程自己写了一个web站点文件下载的小项目，该项目中还加入了简单的反盗链技术。

　　1、首先创建一个SharedFilesServlet用于返回一个文件分享界面

 1 package com.hyman.view;
 2 
 3 import java.io.IOException;
 4 import java.io.PrintWriter;
 5 
 6 import javax.servlet.ServletException;
 7 import javax.servlet.http.HttpServlet;
 8 import javax.servlet.http.HttpServletRequest;
 9 import javax.servlet.http.HttpServletResponse;
10 
11 /**
12  * Servlet implementation class SharedFilesServlet
13  */
14 public class SharedFilesServlet extends HttpServlet {
15     private static final long serialVersionUID = 1L;
16        
17     /**
18      * @see HttpServlet#HttpServlet()
19      */
20     public SharedFilesServlet() {
21         super();
22         // TODO Auto-generated constructor stub
23     }
24 
25     /**
26      * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
27      */
28     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
29         // TODO Auto-generated method stub
30         response.setContentType("text/html; charset=utf-8"); 
31         PrintWriter out = response.getWriter();
32         out.println("<script type='text/javascript' language='javascript'>"
33                 + "function fileDown(obj){"
34                 + "var resourceName = '';"
35                 + "var buttonId = obj.getAttribute('id');"
36                 + "var eleName = buttonId.substring(0,3) + 'File';"            
37                 + "resourceName = document.getElementsByName(eleName)[0].value;"
38                 + "var url = '/SharingSite/DownFileServlet?fileName=' + resourceName;"
39                 + "window.location.href=url;"
40                 + "}"
41                 + "</script>");
42         out.println("<h1>文件共享网站</h1>");
43         out.println("mp3资源：<input type='text' name='mp3File' />&nbsp;&nbsp;&nbsp;&nbsp;<input type='submit' value ='点击下载' id='mp3Down' onclick='fileDown(this)' /><br/>");
44         out.println("avi资源：<input type='text' name='aviFile' />&nbsp;&nbsp;&nbsp;&nbsp;<input type='submit' value ='点击下载' id='aviDown' onclick='fileDown(this)' /><br/>");
45         out.println("jpg资源：<input type='text' name='jpgFile' />&nbsp;&nbsp;&nbsp;&nbsp;<input type='submit' value ='点击下载' id='jpgDown' onclick='fileDown(this)' /><br/>");
46         out.println("txt资源：<input type='text' name='txtFile' />&nbsp;&nbsp;&nbsp;&nbsp;<input type='submit' value ='点击下载' id='txtDown' onclick='fileDown(this)' /><br/>");
47     }
48 
49     /**
50      * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
51      */
52     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
53         // TODO Auto-generated method stub
54         this.doGet(request, response);
55     }
56 
57 }

　　2、然后创建一个控制器，来判断是否盗链，以及处理文件下载逻辑：

 1 package com.hyman.controller;
 2 
 3 import java.io.File;
 4 import java.io.FileInputStream;
 5 import java.io.IOException;
 6 import java.io.OutputStream;
 7 
 8 import javax.servlet.ServletException;
 9 import javax.servlet.http.HttpServlet;
10 import javax.servlet.http.HttpServletRequest;
11 import javax.servlet.http.HttpServletResponse;
12 
13 /**
14  * Servlet implementation class DownFileServlet
15  */
16 public class DownFileServlet extends HttpServlet {
17     private static final long serialVersionUID = 1L;
18        
19     /**
20      * @see HttpServlet#HttpServlet()
21      */
22     public DownFileServlet() {
23         super();
24         // TODO Auto-generated constructor stub
25     }
26 
27     /**
28      * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
29      */
30     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
31         // TODO Auto-generated method stub
32         response.setContentType("text/html; charset=utf-8");
33         String referer = request.getHeader("Referer");
34         if (referer == null || !referer.startsWith("http://localhost:8080/SharingSite/")) {
35             response.sendRedirect("/SharingSite/AntiPirateLink");
36         } else {
37             String fileName = request.getParameter("fileName");
38             response.setHeader("Content-Disposition", "attachment; filename="+fileName);
39             String path = this.getServletContext().getRealPath("/resources/"+fileName);
40             FileInputStream fis = null;
41             OutputStream os = null;
42             try {
43                 fis = new FileInputStream(new File(path));
44                 byte buff[] = new byte[1024];
45                 int len = 0;
46                 os = response.getOutputStream();
47                 while ((len = fis.read(buff)) > 0) {
48                     os.write(buff, 0, len);
49                 }
50             } catch (Exception e) {
51                 e.printStackTrace();
52                 throw new RuntimeException();
53             } finally {
54                 if (os != null) os.close();
55                 if (fis != null) fis.close();
56             }
57         }
58         
59     }
60 
61     /**
62      * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
63      */
64     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
65         // TODO Auto-generated method stub
66         this.doGet(request, response);
67     }
68 
69 }

　　3、创建一个AntiPirateLink返回盗链提醒界面，并在10秒后自动刷新跳转到SharedFilesServlet

 1 package com.hyman.view;
 2 
 3 import java.io.IOException;
 4 import java.io.PrintWriter;
 5 
 6 import javax.servlet.ServletException;
 7 import javax.servlet.http.HttpServlet;
 8 import javax.servlet.http.HttpServletRequest;
 9 import javax.servlet.http.HttpServletResponse;
10 
11 /**
12  * Servlet implementation class AntiPirateLink
13  */
14 public class AntiPirateLink extends HttpServlet {
15     private static final long serialVersionUID = 1L;
16        
17     /**
18      * @see HttpServlet#HttpServlet()
19      */
20     public AntiPirateLink() {
21         super();
22         // TODO Auto-generated constructor stub
23     }
24 
25     /**
26      * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
27      */
28     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
29         // TODO Auto-generated method stub
30         response.setContentType("text/html; charset=utf-8");
31         PrintWriter out = response.getWriter();
32         out.println("<script type='text/javascript' language='javascript'>"
33                 + "var i = 10;"
34                 + "function showTime(){"
35                 + "if(i > 0) {document.getElementById('time').innerHTML = '请不要盗链下载... ' + i +' 秒后自动跳转到下载首页...';"
36                 + "i--;}"
37                 + "}"
38                 + "setInterval('showTime()',1000);"
39                 + "</script>");
40         out.println("<span id='time'></span>");
41         response.setHeader("Refresh", "10; url=/SharingSite/SharedFilesServlet");
42     }
43 
44     /**
45      * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
46      */
47     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
48         // TODO Auto-generated method stub
49         this.doGet(request, response);
50     }
51 
52 }

【分析】文件下载部分实现步骤：

1、response.setHeader("Content-Disposition", "attachment; filename="+fileName);在http回复消息头中的Content-Disposition中指明下文件的文件名；
2、调用this.getServletContext().getRealPath("/resources/"+fileName);函数获取到文件的全路径；
3、使用文件流FileInputStream将文件读入到服务器内存，重要要用到缓存处理，然后再调用response的getOutputStream()方法获得向客户端写文件的输出文件流；