java通过jsp+javaBean+servlet实现下载功能

　　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：<a href="FileDownloadServlet.do?id=<%=announ.getId() %>&attachment_1path=<%=announ.getAttachment_1path()%>"><%=announ.getAttachment_1()%></a><br>

                <%} %>

                <%

        if(!"".equals(announ.getAttachment_2())&&announ.getAttachment_2()!=null&&!"null".equals(announ.getAttachment_2())){

         %>

                附件：<a href="FileDownloadServlet.do?id=<%=announ.getId() %>&attachment_2path=<%=announ.getAttachment_2path() %>"><%=announ.getAttachment_2()%></a><br>

                <%} %>