前些天做一个小项目需要在页面点击文件名实现功能，下面对实现的过程做简单的记录。 首先需要从静态页面获取需要下载文件的文件名，如代码中的attachment_1path,如果需要从数据库调用，则可以通过id查询出路径，下载功能的servlet如下：

public void doPost(HttpServletRequest request, HttpServletResponse response)            throws ServletException, IOException {        //String id=request.getParameter("id");        String attachment_1path=request.getParameter("attachment_1path");        System.out.println(attachment_1path);//检测attachment_1path        String attachment_2path=request.getParameter("attachment_2path");        System.out.println("attachment_2-----"+attachment_2path);        String attachment_3path=request.getParameter("attachment_3path");        System.out.println("-------3"+attachment_3path);        String attachment=""; //判断三个下载链接中哪个被用户选择，然后把该值赋给attachment，以便实现代码公用        if(("".equals(attachment_3path)||("null".equals(attachment_3path))||(attachment_3path==null))&&(("".equals(attachment_2path))||("null".equals(attachment_2path))||(attachment_2path==null))){            attachment=attachment_1path;            System.out.println(attachment_1path);        }else if((("".equals(attachment_1path))||("null".equals(attachment_1path))||(attachment_1path==null))&&(("".equals(attachment_3path))||("null".equals(attachment_3path))||(attachment_3path==null))){            attachment=attachment_2path;        }else if((("".equals(attachment_2path))||("null".equals(attachment_2path))||(attachment_2path==null))&&(("".equals(attachment_1path))||("null".equals(attachment_1path))||(attachment_1path==null))){            attachment=attachment_3path;            System.out.println(attachment);                    }     //实现文件下载动作        FileUtil fu=new FileUtil();                    int r=fu.download(this.getServletContext(), response, attachment);     } //下载文件的方法，参数Map存储下载文件信息，包括文件地址file        public int download(ServletContext servletContext,HttpServletResponse response,String attachment) throws IOException{

BufferedInputStream bis = null;                   BufferedOutputStream bos = null;                        try {                    String filePath="/upload/attachments";//此处为下载文件的相对路径                    String realPath=servletContext.getRealPath(filePath);//此处获得文件相对路径的绝对路径                                       response.setContentType("multipart/form-data;charset=utf-8");//设置类型，每次下载会判断下载文件的类型                                        response.setHeader("Content-disposition", "attachment; filename=" + attachment);   //attachment为文件名                        File file=new File(realPath+"\\"+attachment);                                       FileInputStream filebuffer=new FileInputStream(file);                    bis = new BufferedInputStream(filebuffer);                      bos = new BufferedOutputStream(response.getOutputStream());                                           byte[] buff = new byte[1024*1000];                       int bytesRead;                        while ((bytesRead = bis.read(buff, 0, buff.length))!=-1) {             //read()方法读入从字节buff的第一个字符到buff最后一个字节，      　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　//如果为第一次读入则返回-1，否则返回实际读入的字节数                        bos.write(buff, 0, bytesRead);                       //实现字节刘写入                      }                                } catch (IOException e) {                   return 0;            } finally {                             bis.close();                               bos.flush();                    bos.close();               }            return 1;        }

 以下为jsp页面获得数据库中存储的文件实际存储文件名，并判断：如果文件名为空则不显示，只有在不为空的时候才显示附件内容，并完成传递参数给servlet的任务，如下：

 

<%        if(!"".equals(announ.getAttachment_1())&&announ.getAttachment_1()!=null&&!"null".equals(announ.getAttachment_1())){         %>                附件：<%=announ.getAttachment_1()%>
                <%} %>                <%        if(!"".equals(announ.getAttachment_2())&&announ.getAttachment_2()!=null&&!"null".equals(announ.getAttachment_2())){         %>                附件：<%=announ.getAttachment_2()%>
                <%} %>