本文实例为大家分享了jsp实现文件下载功能的3种方法，供大家参考，具体内容如下

第一种、采用转发的方式：

package cn.jbit.download.servlet; 
 
import java.io.IOException; 
 
import javax.servlet.RequestDispatcher; 
import javax.servlet.ServletException; 
import javax.servlet.http.HttpServlet; 
import javax.servlet.http.HttpServletRequest; 
import javax.servlet.http.HttpServletResponse; 
 
public class DownloadServlet extends HttpServlet { 
 
  private static final long serialVersionUID = 6765085208899952414L; 
 
  public void doGet(HttpServletRequest request, HttpServletResponse response) 
      throws ServletException, IOException { 
    doPost(request, response); 
  } 
 
  public void doPost(HttpServletRequest request, HttpServletResponse response) 
      throws ServletException, IOException { 
    String filedownload = "/upload/1/10213.jpg";//即将下载的文件的相对路径 
    String filedisplay = "10213.jpg";//下载文件时显示的文件保存名称 
    response.setContentType("application/x-download");//设置为下载application/x-download 
    //response.setContentType("application/x-msdownload");//设置为下载application/x-msdownload 
    //response.setContentType("application/octet-stream");//设置为下载application/octet-stream 
    response.addHeader("Content-Disposition", "attachment;filename=" 
        + filedisplay); 
     
    try { 
      RequestDispatcher rd = request.getRequestDispatcher(filedownload); 
      if(rd != null) 
      { 
        rd.forward(request,response); 
      } 
      response.flushBuffer(); 
    } catch (Exception e) { 
      e.printStackTrace(); 
    } 
  } 
} 

二、通过输出流的方式：

package cn.jbit.download.servlet; 
 
import java.io.BufferedInputStream; 
import java.io.BufferedOutputStream; 
import java.io.File; 
import java.io.FileInputStream; 
import java.io.IOException; 
import java.io.InputStream; 
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 DownloadOfIOServlet extends HttpServlet { 
 public void doGet(HttpServletRequest request, HttpServletResponse response) 
      throws ServletException, IOException { 
    doPost(request, response); 
  } 
   
  public void doPost(HttpServletRequest request, HttpServletResponse response) 
      throws ServletException, IOException { 
    String basePath = request.getSession().getServletContext().getRealPath("/upload"); 
 
    String filedisplay = "helloworld.jpg"; 
    String filedownload = basePath + File.separator + "helloworld.jpg"; 
    response.setContentType("applicaiton/x-download"); 
    response.addHeader("Content-Disposition", "attachment;filename="+filedisplay); 
     
    InputStream is = null; 
    OutputStream os = null; 
    BufferedInputStream bis = null; 
    BufferedOutputStream bos = null; 
     
    is = new FileInputStream(new File(filedownload)); 
    bis = new BufferedInputStream(is); 
    os = response.getOutputStream(); 
    bos = new BufferedOutputStream(os); 
     
    byte[] b = new byte[1024]; 
    int len = 0; 
    while((len = bis.read(b)) != -1){ 
      bos.write(b,0,len); 
    } 
     
    bis.close(); 
    is.close(); 
    bos.close(); 
    os.close(); 
  } 
} 

第三种、通过超链接的方式(注意不推荐，因为会暴露下载文件的位置)