package cn.itcast.download;

 import javax.servlet.ServletException;

 import javax.servlet.ServletOutputStream;

 import javax.servlet.annotation.WebServlet;

 import javax.servlet.http.HttpServlet;

 import javax.servlet.http.HttpServletRequest;

 import javax.servlet.http.HttpServletResponse;

 import java.io.FileInputStream;

 import java.io.IOException;

 @WebServlet("/001")

 public class DownloadServlet extends HttpServlet {

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

         //获取资源名

         String filename = request.getParameter("filename");

         //获取资源对应输入流

         FileInputStream fis = new FileInputStream(request.getServletContext().getRealPath("/download/" + filename));

         //告知类型

         response.setContentType(request.getServletContext().getMimeType(filename));

         //告知下载

         response.setHeader("content-disposition", "attachment;filename=" + filename);

         //获取响应输出流

         ServletOutputStream sos = response.getOutputStream();

         //写数据

         byte[] bys = new byte[1024 * 8];

         int len;

         while((len = fis.read(bys)) != -1){

             sos.write(bys, 0, len);

         }

         //释放资源

         fis.close();

     }

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

         doPost(request, response);

     }

 }

 package cn.itcast.download;

 import javax.servlet.ServletException;

 import javax.servlet.ServletOutputStream;

 import javax.servlet.annotation.WebServlet;

 import javax.servlet.http.HttpServlet;

 import javax.servlet.http.HttpServletRequest;

 import javax.servlet.http.HttpServletResponse;

 import java.io.FileInputStream;

 import java.io.IOException;

 import java.net.URLEncoder;

 import java.util.Base64;

 @WebServlet("/download")

 public class DownloadServlet2 extends HttpServlet {

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

         //获取资源名

         String filename = request.getParameter("filename");

         //获取资源对应输入流

         FileInputStream fis = new FileInputStream(request.getServletContext().getRealPath("/download/" + filename));

         //告知类型

         response.setContentType(request.getServletContext().getMimeType(filename));

         //告知下载

         //处理响应头乱码，浏览器兼容性问题

         String agent = request.getHeader("user-agent");

         String fileNameEnc = null;

         if(agent.contains("MSIE")){

             fileNameEnc = URLEncoder.encode(filename,"UTF-8").replace("+", " ");

         }else if(agent.contains("Firefox")){

             fileNameEnc = "=?utf-8?B?"

                     + Base64.getEncoder().encodeToString(filename.getBytes("UTF-8"))

                     + "?=";

         }else{

             fileNameEnc = URLEncoder.encode(filename,"UTF-8");

         }

         response.setHeader("content-disposition", "attachment;filename=" + fileNameEnc);

         //获取响应输出流

         ServletOutputStream sos = response.getOutputStream();

         //写数据

         byte[] bys = new byte[1024 * 8];

         int len;

         while((len = fis.read(bys)) != -1){

             sos.write(bys, 0, len);

         }

         //释放资源

         fis.close();

     }

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

         doPost(request, response);

     }

 }