文件的下载

1.利用响应输出流进行文件的下载：response.getOutputStream();

关键技术：

本实例主要设置响应头的信息和输出流进行实现：在servlet中

设置响应头：response.setContextType("application/x-msdownFile")

2.设置响应头：response.setHeader("content-Disposition","attachment; filename=" +java.net.URLEncoder.encode(filename,"utf-8"));

下面使用响应流在Servlet：

 1     System.out.println("dounload servlet");
 2         String path=request.getParameter("path");
 3         // JSP 页面上超链接方式，不是同一个request请求，Session att=null
 4         String att=(String) request.getAttribute("path1");
 5         
 6         
 7         InputStream in=getServletContext().getResourceAsStream("/WEB-INF/files/"+path);
 8         
 9         if(in ==null)
10         {
11             request.getRequestDispatcher("/APP/404.jsp").forward(request, response);;
12         }
13         //以响应流方式输出对象
14         response.setCharacterEncoding("UTF-8");
15         response.setContentType("application/x-msdownload"); 
16         String fileName=path;
17         response.setHeader("Content-Disposition", "attachment;filename=" + URLEncoder.encode(fileName, "UTF-8"));
18         OutputStream out=response.getOutputStream();
19         byte[] buffer=new byte[1024];
20         
21         int len=0;
22         while((len=in.read(buffer))!=-1)
23         {
24             out.write(buffer,0,len);
25         }
26             in.close();

注意：将文件名转换成UTF-8，使用流的方式注意编码的方式设置成一致，造成文件名出现乱码，JSP页面的编码方式和response.setCharacterEncoding("utf-8")

2.防止网站文件盗链接下载：

关键技术：应用request对象中getHeader（）的方法，获取getHeader中referer字段，该值记录了当前请求的上一次访问的地址，

 1 String from=request.getHeader("Referer");
 2         System.out.println(from);
 3         if(from==null || (from.indexOf("localhost:8080/day_04")<0))
 4             request.getRequestDispatcher("/APP/404.jsp").forward(request, response);;
 5         
 6         System.out.println("dounload servlet");
 7         String path=request.getParameter("path");
 8         // JSP 页面上超链接方式，不是同一个request请求，Session att=null
 9         
10         
11         String att=(String) request.getAttribute("path1");
12         
13         
14         InputStream in=getServletContext().getResourceAsStream("/WEB-INF/files/"+path);
15         
16         if(in ==null)
17         {
18             request.getRequestDispatcher("/APP/404.jsp").forward(request, response);;
19         }
20         //以响应流方式输出对象
21         response.setCharacterEncoding("UTF-8");
22         response.setContentType("application/x-msdownload"); 
23         String fileName=path;
24         response.setHeader("Content-Disposition", "attachment;filename=" + URLEncoder.encode(fileName, "UTF-8"));
25         OutputStream out=response.getOutputStream();
26         byte[] buffer=new byte[1024];
27         
28         int len=0;
29         while((len=in.read(buffer))!=-1)
30         {
31             out.write(buffer,0,len);
32         }
33             in.close();

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