Servlet——使用http响应头Content-Disposition下载文件的示例

项目目录如上所示，图片jpg和音乐mp3存在web应用中，而影音mp4不在web应用目录中。

首先，写了一个简单的下载页面download.html，提供下载链接，如下：

  
    
	
    
    
    
    
    

  
  
  
  	
下载列表
	

  	
音乐
  	

  		
Avicii Conrad Sewell - Taste the Feeling
  		
Madonna - Living For Love
  		
Sam Smith - Lay Me Down
  		
Tanaki Alison - Reach Higher
  		
Tep No - Me And My Guitar
  	
  	

  	
图片
  	

  		
cat (1)
  		
cat (2)
  		
cat (3)
  		
cat (4)
  		
cat (5)
  		
cat (6)
  		
cat (7)
  		
cat (8)
  		
cat (9)
  		
cat (10)
  	
  	

  	
影音
  	

  		
Kawhi Leonard Career Big Movie - Evolving In Silence
  		
Monkey.King.Hero.is.Back.2015
  	
  

注意到，所有的下载链接都指向了/DownFileTest/DownFileServlet，并且后面跟着filename这个参数。

该页面运行结果如下所示：

那么，DownFileServlet.java如下所示：

package com.gavin.download;
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;


public class DownFileServlet extends HttpServlet {

	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		response.setContentType("text/html;charset=utf-8");
		// request通过getParameter得到filename这个参数的值
		String filename = request.getParameter("filename");
		System.out.println(filename);
		// response设置Content-Disposition
		response.setHeader("Content-Disposition", "attachment;filename="+filename);
		String path = null;
		// jpg和mp3都存在于web应用目录下，mp4则存在于F盘的movie文件夹下
		// 如果是jpg或者mp3则通过它们的相对路径得到绝对路径
		if(filename.endsWith("jpg")){
			path= this.getServletContext().getRealPath("/images/"+filename);
		}else if (filename.endsWith("mp3")){
			path= this.getServletContext().getRealPath("/musics/"+filename);
		}else if(filename.endsWith("mp4")){
			path = "F:\\movie\\"+filename;
		}
		FileInputStream fis = new FileInputStream(path);
		byte buff[] = new byte[2048];
		int len = 0;
		OutputStream os = response.getOutputStream();
		while((len = fis.read(buff))>0){
			os.write(buff, 0, len);
		}
		os.close();
		fis.close();
	}

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		this.doGet(request, response);
	}

}

此时示例已经完成，每一次请求DownFileServlet，该Servlet都通过request得到filename这个参数的值，并判断后缀来得到资源的全路径，然后通过字节流传递给客户端。