jsp 附件下载的实现
一、实现功能：页面上显示附件链接，点击链接，弹出“文件下载”框，打开或保存文件。
（ps:最简单常见的功能，却有很多地方需要注意）
二、过程：采用 servlet1 提供“附件列表”数据，在页面显示所有附件链接，点击链接经过servlet2处理，弹出“文件下载”框，打开或保存文件。
1、在index页面，通过点击链接向GotoAttachServlet发出请求。
2、GotoAttachServlet 提供附件列表，转向download.jsp 页面。
3、在download.jsp 点击某个附件链接，通过DownloadServlet处理，弹出“文件下载”框，打开或保存该文件。
注:为了方便，数据没有从数据库中取。整个过程是完整的，其实只要关注DownloadServlet.java中相关代码即可。
三、实现。
1、index中的相关代码。
<a href="GotoAttachServlet">附件页面</a>
2、GotoAttachServlet中相关代码。
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
List<Attachment>attachList = new ArrayList<Attachment>();
Attachment attach1=new Attachment(1,"flower.png","d://flower.jpg");
attachList.add(attach1);
Attachment attach2=new Attachment(2,"tree.txt","d://tree.txt");
attachList.add(attach2);
request.setAttribute("attachList", attachList);
request.getRequestDispatcher("download.jsp").forward(request, response);
}
3、download.jsp 代码。
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<%@taglib uri="http://java.sun.com/jsp/jstl/fmt" prefix="fmt" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>下载</title>
<script src="<%=basePath%>js/jquery-1.4.4.js"></script>
<script type="text/javascript">
function download(attachId){
var url="/MyWeb/DownloadServlet?attachId="+attachId;
$('#attachmentForm').attr('action',url).submit();
}
</script>
</head>
<body>
<div>附件下载</div>
<form id="attachmentForm" method="post">
<table>
<tr>
<td>附件：</td>
<td>
<ul>
<c:forEach items="${attachList}" var="attach">
<li>
<a href="#" onclick="download('${attach.id}')">${attach.name}</a>
</li>
</c:forEach>
</ul>
</td>
</tr>
</table>
</form>
</body>
</html>
4、DownLoadServlet.java中相关代码。
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String idStr=request.getParameter("attachId");
Attachment attachment=null;
if(idStr.equals("1")){
attachment=new Attachment(1,"flower.png","d://flower.jpg");
}else{
attachment=new Attachment(2,"tree.txt","d://tree.txt");
}
String downFilePath=attachment.getPath();
String fileName = attachment.getName();
fileName = URLEncoder.encode(fileName, "UTF-8");
// 设置响应信息
response.reset();
response.setContentType("application/octet-stream");
response.addHeader("Content-Disposition", "attachment;filename="
+ fileName);
response.setCharacterEncoding("utf-8");
// 得到流
InputStream inputStream = new FileInputStream(downFilePath);
ServletOutputStream servletOutputStream=response.getOutputStream();
final int size = 1024;
byte[] buffer = new byte[size];
int length;
while ((length = inputStream.read(buffer)) > 0) {
servletOutputStream.write(buffer, 0, length);
}
servletOutputStream.flush();
servletOutputStream.close();
} }
5、你可能看不明白的地方：
1、response.setContentType("application/octet-stream"); 参看：http://wuyechun.iteye.com/blog/1132423
2、response.addHeader("Content-Disposition", "attachment;filename=" + fileName);
在使用来自 Web 服务器的文档时，您可能希望立即提示用户将文件直接保存在用户磁盘上，而不要在浏览器中打开该文件。不过，对于已知的 MIME（多用途 Internet 邮件扩展）类型，如 Microsoft Word ("application/ms-word")，默认行为是在 Internet Explorer 中打开文档。
可以使用 Content-disposition 头来覆盖此默认行为。其格式是：
Content-disposition: attachment; filename=fname.ext