Read a catalog from a file.
This class reads a catalog from a URL.
@param catalog The catalog for which this reader is called.
@param fileUrl The URL of a document to be read.
@throws MalformedURLException if the specified URL cannot beturned into a URL object.
@throws IOException if the URL cannot be read.
@throws UnknownCatalogFormatException if the catalog format isnot recognized.
@throws UnparseableCatalogException if the catalog cannot be parsed.(For example, if it is supposed to be XML and isn't well-formed.)