大文件下载防止内存溢出

	response.reset();
	response.setContentType("application/octet-stream;charset=UTF-8");
	response.setHeader("Accept-ranges", "bytes");
	response.addHeader("Content-Disposition", "attachment; filename=\""+fileName+".zip\"");
	FileInputStream fis = new FileInputStream(zipFile);
	int len = -1;
	byte[] bytes = new byte[1024];
	while ((len = fis.read(bytes)) != -1) {
		//将文件读入压缩文件内
		response.getOutputStream().write(bytes, 0, len);
		response.flushBuffer();
	}
	fis.close();