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' />    <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' />    <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' />    <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' />    <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；