Servlet實現web站點文件下載功能示例

1、首先創建一個SharedFilesServlet用于返回一個文件分享界面

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>文件共享網站</h1>");
 out.println("mp3資源：<input type='text' name='mp3File' />&nbsp;&nbsp;&nbsp;&nbsp;<input type='submit' value ='點擊下載' id='mp3Down' onclick='fileDown(this)' /><br/>");
 out.println("avi資源：<input type='text' name='aviFile' />&nbsp;&nbsp;&nbsp;&nbsp;<input type='submit' value ='點擊下載' id='aviDown' onclick='fileDown(this)' /><br/>");
 out.println("jpg資源：<input type='text' name='jpgFile' />&nbsp;&nbsp;&nbsp;&nbsp;<input type='submit' value ='點擊下載' id='jpgDown' onclick='fileDown(this)' /><br/>");
 out.println("txt資源：<input type='text' name='txtFile' />&nbsp;&nbsp;&nbsp;&nbsp;<input type='submit' value ='點擊下載' 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);
}



}</pre> 


 2、然后創建一個控制器，來判斷是否盜鏈，以及處理文件下載邏輯： 

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/&quot;)) {

 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);
}



}</pre> 


 3、創建一個AntiPirateLink返回盜鏈提醒界面，并在10秒后自動刷新跳轉到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 = '請不要盜鏈下載... ' + i +' 秒后自動跳轉到下載首頁...';"
     + "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);
}



}</pre> 


 【分析】文件下載部分實現步驟： 
 【分析】文件下載部分實現步驟： 

 

 1、response.setHeader("Content-Disposition", "attachment; filename="+fileName);在http回復消息頭中的Content-Disposition中指明下文件的文件名； 

 2、調用this.getServletContext().getRealPath("/resources/"+fileName);函數獲取到文件的全路徑； 

 3、使用文件流FileInputStream將文件讀入到服務器內存，重要要用到緩存處理，然后再調用response的getOutputStream()方法獲得向客戶端寫文件的輸出文件流；

 

 來自：
http://www.cnblogs.com/page-of-Hyman/p/4321523.html