Servlet 输出文件下载

1、如果下载的文件名是中文：
     将文件名重新用“ISO8859_1”编码

2、下载自定义文件名：
     Response 设置头文件类型 “Content-disposition”，值为“ attachment;filename="文件名" ”

3、获取文件的MIME类型
     通过 ServletContext 的 getMimeType(String filename)，即通过文件的后缀名得到注册在tomcat中的相应MIME类型

4、实例（要下载的文件在WebRoot/file/模版文件.xls）：

@Override
	public void doGet(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		req.setCharacterEncoding("UTF-8");
		String referPath = req.getHeader("Refer");
		String fileName = req.getSession()
								.getServletContext()
								.getRealPath("/")+"file/temp.xls";
		File file = new File(fileName);
		if (file == null || !file.exists() ) {
			System.out.println("文件不存在 : "+fileName);
			resp.sendRedirect(referPath);
		}
		
		resp.setCharacterEncoding("UTF-8");
		
		String fileType = req.getSession()
								.getServletContext()
								.getMimeType(fileName);
		if (fileType==null) {
			fileType = "application/octet-stream";
		}
		resp.setContentType(fileType);
		System.out.println("文件类型是："+fileType);
		String newFileName = new String("模版文件.xls".getBytes(), "ISO8859_1");
		resp.setHeader("Content-disposition", "attachment;filename=\""+newFileName+"\"");
		
		BufferedInputStream bis = new BufferedInputStream(new FileInputStream(file));
		BufferedOutputStream bos = new BufferedOutputStream(resp.getOutputStream());
		
		byte[] buffer = new byte[1024];
		int length = 0;
		
		while((length = bis.read(buffer)) != -1){
			bos.write(buffer, 0, length);
		}
		
		if (bis != null) bis.close();
		if (bos != null) bos.close();
	}