XML catalog

The following simple catalog shows how one might provide locally cached DTDs for an XHTML page validation tool, for example. This catalog makes it possible to resolve -//W3C//DTD XHTML 1.0 Strict//EN to the local URI dtd/xhtml1/xhtml1-strict.dtd. Similarly, it provides local URIs for two other public IDs. Note that the document above includes a DOCTYPE – this may cause the parser to attempt to access the system ID URL for the DOCTYPE (i.e. http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd) before the catalog resolver is fully functioning, which is probably undesirable. To prevent this, simply remove the DOCTYPE declaration. The following example shows this, and also shows the equivalent <system/> declarations as an alternative to <public/> declarations. ==Using a catalog – Java SAX example==

Catalog resolvers are available for various programming languages. The following example shows how, in Java, a SAX parser may be created to parse some input source in which the org.apache.xml.resolver.tools.CatalogResolver is used to resolve external entities to locally cached instances. This resolver originates from Apache Xerces but is now included with the Sun Java runtime. It is necessary to create a SAXParser in the standard way by using factories. The XML reader entity resolver should be set to the default or to a customly-made one. final SAXParser saxParser = SAXParserFactory.newInstance().newSAXParser(); final XMLReader reader = saxParser.getXMLReader(); final ContentHandler handler = ...; final InputSource input = ...; reader.setEntityResolver(new CatalogResolver()); reader.setContentHandler(handler); reader.parse(input); It is important to call the parse method on the reader, not on the SAX parser. ==External references==

• XML Catalogs, OASIS Standard V1.1, 7 October 2005 • XML Entity and URI Resolvers, Sun • XML Catalog Manager project on SourceForge