Java开发之文件下载详解编程语言

    package com.example.web;   
       
    import java.io.File;   
    import java.io.FileInputStream;   
    import java.io.IOException;   
    import java.io.InputStream;   
    import java.io.OutputStream;   
    import java.net.URLEncoder;   
       
    import javax.servlet.ServletException;   
    import javax.servlet.http.HttpServlet;   
    import javax.servlet.http.HttpServletRequest;   
    import javax.servlet.http.HttpServletResponse;   
       
    import org.apache.commons.io.IOUtils;   
       
    public class Download extends HttpServlet {   
       
        public void doGet(HttpServletRequest request, HttpServletResponse response)   
                throws ServletException, IOException {   
            response.setContentType("text/html;charset=utf-8");   
            OutputStream out=response.getOutputStream();   
            //获取要下载的文件名   
            String fileName=request.getParameter("loadname");   
            fileName=new String(fileName.getBytes("ISO-8859-1"),"UTF-8");   
            //得到下载文件的路径   
            String storPath=getServletContext().getRealPath("WEB-INF/files");   
            //得到源文件名   
            String oldName=fileName.split("_")[1];   
            //进一步根据hashcode来确定子文件夹   
            String childPath=generateDir(storPath,fileName);   
            //判断要下载的文件是否还存在   
            File file=new File(storPath+File.separator+childPath+File.separator+fileName);   
            if(!file.exists()){   
                out.write("你要下载的资源可能不存在".getBytes());   
            }else{   
                //如果存在就进行下载操作   
                InputStream is=new FileInputStream(file);   
                //指明下载的响应头   
                response.setHeader("Content-Disposition",    
                        "attachment;filename="+URLEncoder.encode(oldName,"UTF-8"));   
                IOUtils.copy(is, out);   
                is.close();   
            }   
        }   
        private String generateDir(String storePath, String fileName) {   
            int hashcode=fileName.hashCode();   
            int dir1=hashcode &  0xf;   
            int dir2=(hashcode & 0xf0)>>4;   
            String childPath=dir1+File.separator+dir2;   
            File file=new File(storePath,childPath);   
            if(!file.exists()){   
                file.mkdirs();   
            }   
            return childPath;   
        }   
        public void doPost(HttpServletRequest request, HttpServletResponse response)   
                throws ServletException, IOException {   
            this.doGet(request, response);   
       
        }   
       
    }