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

 package com.hyman.view;

 import java.io.IOException;
 import java.io.PrintWriter;

 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;

 /**
  * Servlet implementation class SharedFilesServlet
  */
 public class SharedFilesServlet extends HttpServlet {
     private static final long serialVersionUID = 1L;

     /**
      * @see HttpServlet#HttpServlet()
      */
     public SharedFilesServlet() {
         super();
         // TODO Auto-generated constructor stub
     }

     /**
      * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
      */
     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
         // TODO Auto-generated method stub
         response.setContentType("text/html; charset=utf-8");
         PrintWriter out = response.getWriter();
         out.println("<script type='text/javascript' language='javascript'>"
                 + "function fileDown(obj){"
                 + "var resourceName = '';"
                 + "var buttonId = obj.getAttribute('id');"
                 + "var eleName = buttonId.substring(0,3) + 'File';"
                 + "resourceName = document.getElementsByName(eleName)[0].value;"
                 + "var url = '/SharingSite/DownFileServlet?fileName=' + resourceName;"
                 + "window.location.href=url;"
                 + "}"
                 + "</script>");
         out.println("<h1>文件共享网站</h1>");
         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/>");
         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/>");
         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/>");
         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/>");
     }

     /**
      * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
      */
     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
         // TODO Auto-generated method stub
         this.doGet(request, response);
     }

 }

　　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：

 package com.hyman.controller;

 import java.io.File;
 import java.io.FileInputStream;
 import java.io.IOException;
 import java.io.OutputStream;

 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;

 /**
  * Servlet implementation class DownFileServlet
  */
 public class DownFileServlet extends HttpServlet {
     private static final long serialVersionUID = 1L;

     /**
      * @see HttpServlet#HttpServlet()
      */
     public DownFileServlet() {
         super();
         // TODO Auto-generated constructor stub
     }

     /**
      * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
      */
     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
         // TODO Auto-generated method stub
         response.setContentType("text/html; charset=utf-8");
         String referer = request.getHeader("Referer");
         if (referer == null || !referer.startsWith("http://localhost:8080/SharingSite/")) {
             response.sendRedirect("/SharingSite/AntiPirateLink");
         } else {
             String fileName = request.getParameter("fileName");
             response.setHeader("Content-Disposition", "attachment; filename="+fileName);
             String path = this.getServletContext().getRealPath("/resources/"+fileName);
             FileInputStream fis = null;
             OutputStream os = null;
             try {
                 fis = new FileInputStream(new File(path));
                 byte buff[] = new byte[1024];
                 int len = 0;
                 os = response.getOutputStream();
                 while ((len = fis.read(buff)) > 0) {
                     os.write(buff, 0, len);
                 }
             } catch (Exception e) {
                 e.printStackTrace();
                 throw new RuntimeException();
             } finally {
                 if (os != null) os.close();
                 if (fis != null) fis.close();
             }
         }

     }

     /**
      * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
      */
     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
         // TODO Auto-generated method stub
         this.doGet(request, response);
     }

 }

　　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

 package com.hyman.view;

 import java.io.IOException;
 import java.io.PrintWriter;

 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;

 /**
  * Servlet implementation class AntiPirateLink
  */
 public class AntiPirateLink extends HttpServlet {
     private static final long serialVersionUID = 1L;

     /**
      * @see HttpServlet#HttpServlet()
      */
     public AntiPirateLink() {
         super();
         // TODO Auto-generated constructor stub
     }

     /**
      * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
      */
     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
         // TODO Auto-generated method stub
         response.setContentType("text/html; charset=utf-8");
         PrintWriter out = response.getWriter();
         out.println("<script type='text/javascript' language='javascript'>"
                 + "var i = 10;"
                 + "function showTime(){"
                 + "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...';"
                 + "i--;}"
                 + "}"
                 + "setInterval('showTime()',1000);"
                 + "</script>");
         out.println("<span id='time'></span>");
         response.setHeader("Refresh", "10; url=/SharingSite/SharedFilesServlet");
     }

     /**
      * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
      */
     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
         // TODO Auto-generated method stub
         this.doGet(request, response);
     }

 }

【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；