xml document to string for print log

下面代码实现了xml的document转换成string 类型，用于xml输出

/**
	 * write doc to log
	 * @param doc
	 * @throws IOException
	 */
	private static String writeXml(Document doc) throws IOException {
		// write the document to output stream ("out")
		ByteArrayOutputStream out = new ByteArrayOutputStream();;
		OutputFormat format = new OutputFormat(doc);
		XMLSerializer serializer = new XMLSerializer(out, format);
		serializer.serialize(doc.getDocumentElement());
		InputStream is = new ByteArrayInputStream(out.toByteArray());
		StringBuffer stringBuffer = new StringBuffer();
		byte[] b = new byte[1024];
		int len=0;
		while( (len = is.read(b)) > -1 )
		{
			for(int i=0; i<len; i++)
			{
				stringBuffer.append((char)b[i]);
			}
		}
		return stringBuffer.toString();
	}