把字符串解析成xml的时候报错java.net.MalformedURLException: no protocol

public String parserXml(XMLParseSafeCallRes xMLParseSafeCallRes, String returnXml)
throws BusinessException {
XMLSafeResHeader resHeader = null;
InputStream strm = null;
InputSource source = null;

try {
XMLReader parser = XMLReaderFactory.createXMLReader("org.apache.xerces.parsers.SAXParser");

parser.setErrorHandler(new XMLErrorHandler());
parser.setContentHandler(xMLParseSafeCallRes);

// 启用验证(暂时不校验)
parser.setFeature("http://xml.org/sax/features/validation", false);
parser.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", false);

strm = new ByteArrayInputStream(returnXml.getBytes());

source = new InputSource(strm);

// 开始解析文档
parser.parse(source);

resHeader = (XMLSafeResHeader) xMLParseSafeCallRes.getBean().getResBO().getHeader();
} catch (Exception e) {
throw new BusinessException(e.getMessage(), ExceptionCode.InnerError);
}

return resHeader.getResultcode();
}

原代码是用文件流现在改成请求第3方URL返回XML字符串报出“java.net.MalformedURLException: no protocol”异常，解决办法，加入粉色的代码