JS打开文件另存为窗口如何实现

	String serverName = request.getServerName();
	String realPath = request.getRealPath(serverName);// 取得互联网程序的绝对地址
	realPath = realPath.substring(0, realPath.lastIndexOf("\\"));
	String filepath = realPath + "\\downloads\\" ;// 创建文件的保存目录
	String filename = request.getAttribute("xlsFileName") + "";
	File file = null;
	FileInputStream fin = null;
	ServletOutputStream op = null;
	try {
		file = new File(filepath + filename);
		if (!file.exists() || !file.isFile()) {
			System.out.println(filename + "is not existed ");
			return;
		}
		response.reset();
		response.setHeader("Content-Type", "application/vnd.ms-excel");
		response.setHeader("Content-Disposition",
				"attachment; filename=" + filename);
		fin = new FileInputStream(file);
		op = response.getOutputStream();

		File f = new File(filepath);
		if (f.isDirectory()) {
			for (int i = 0; i < f.listFiles().length; i++) {
				File ftmp = f.listFiles()[i];
				ftmp.delete();
			}
		}
		int len;
		byte[] buf = new byte[1024];
		while ((len = fin.read(buf)) != -1) {
			op.write(buf, 0, len);
		}
		op.flush();
	} catch (Exception e) {
		System.out.println(e.getMessage());
	} finally {
		if (op != null) {
			op.close();
			op = null;
		}
		if (fin != null) {
			fin.close();
			fin = null;
		}
	}

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