如何使用XStream框架编码UTF-8？

/**
 *获取报文长度
 */
public static String getNoDataRepXml(Object object) {
    String xml = "";
    try {
        XStream xStream = new XStream();
        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
        //xStream.alias("transaction", RepTransaction.class);
        Writer writer = new OutputStreamWriter(outputStream,"UTF-8");

        xStream.processAnnotations(object.getClass());
        xStream.toXML(object,writer);
        xml = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>" + outputStream.toString("UTF-8");

    } catch (UnsupportedEncodingException e){
        e.printStackTrace();
    }finally {
        return String.format("%08d",xml.getBytes().length)+xml;
    }
}