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);            }        }