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{
;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>
<%} %>
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