关于jsp中的文件下载

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)