'Parses out URL and possible ID for filter-mapping and servlet-mapping.
Pulls url-pattern text out of node and adds to WebXml object. If url-pattern
has an id attribute, adds that as well. This is done for <servlet-mapping>
and <filter-mapping> nodes.
Args:
node: An ElementTreeNode which looks something like the following:
<servlet-mapping>
<servlet-name>redteam</servlet-name>
<url-pattern>/red/*</url-pattern>
</servlet-mapping>'

def _ProcessUrlMappingNode(self, node):

    url_pattern_node = xml_parser_utils.GetChild(node, 'url-pattern')
    if (url_pattern_node is not None):
        self.web_xml.patterns.append(url_pattern_node.text)
        id_attr = xml_parser_utils.GetAttribute(url_pattern_node, 'id')
        if id_attr:
            self.web_xml.pattern_to_id[url_pattern_node.text] = id_attr
