The url-pattern element of a servlet-mapping or a filter-mapping associates a filter or servlet with a set of URLs. When a request arrives, the container uses a simple procedure for matching the URL in the request with a url-pattern in the web.xml file. Mapping Servlets to URLs describes the servlet-mapping element. Mapping Filters to URLs describes the filter-mapping element.

A URL pattern may contain a subset of US-ASCII characters. Other values must be escaped. RFC 2396 describes the legal values for a URL pattern.

Note that HydraExpress matches a URL pattern as a sequence of bytes rather than a sequence of characters. HydraExpress considers URL-escaped and unescaped sequences to be identical. In other words, the URL pattern http://example.com/a/* is identical to the URL pattern http://example.com/%61/*. To represent a character pattern that may have more than one byte sequence, add a mapping for each byte sequence.