/**
* Returns the URI mapping in the catalog for the given external identifier or <code>null</code>
* if no mapping exists. If the system identifier is an URN in the <code>publicid</code> namespace
* it is converted into a public identifier by URN "unwrapping" as specified in the XML Catalogs
* specification.
*
* @param systemId the system identifier to locate in the catalog
* @return the mapped URI or <code>null</code> if no mapping was found in the catalog
* @throws IOException if an i/o error occurred while reading the catalog
*/
public final synchronized String resolveSystem(String systemId) throws IOException {
if (fCatalogsChanged) {
parseCatalogs();
fCatalogsChanged = false;
}
return (fCatalog != null) ? fCatalog.resolveSystem(systemId) : null;
}
