读取xml文件，并转换为Document字节

    public static byte[] getXmlFromFile(String fileName) {
        SAXReader saxReader = new SAXReader();
        byte[] xmlBytes = null;
        try {
            /* 将document中的内容写入文件中 */
            // 默认为UTF-8格式，指定为"GBK"
            FileInputStream in = new FileInputStream(new File(fileName));
            Reader read = new InputStreamReader(in, "GBK");
            Document document = saxReader.read(read);
            document.setXMLEncoding("GBK");
            xmlBytes = document.asXML().getBytes("GBK");
        }
        catch (Exception e) {
            e.printStackTrace();
            log.error("doc2XmlFile error: ", e);
        }
        return xmlBytes;
    }