/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
 
package org.apache.xerces.util;

import java.io.IOException;

import javax.xml.parsers.SAXParserFactory;

import org.apache.xerces.dom.DOMInputImpl;
import org.apache.xerces.jaxp.SAXParserFactoryImpl;
import org.apache.xerces.xni.XMLResourceIdentifier;
import org.apache.xerces.xni.XNIException;
import org.apache.xerces.xni.parser.XMLEntityResolver;
import org.apache.xerces.xni.parser.XMLInputSource;
import org.apache.xml.resolver.Catalog;
import org.apache.xml.resolver.CatalogManager;
import org.apache.xml.resolver.readers.OASISXMLCatalogReader;
import org.apache.xml.resolver.readers.SAXCatalogReader;
import org.w3c.dom.ls.LSInput;
import org.w3c.dom.ls.LSResourceResolver;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.ext.EntityResolver2;

The catalog resolver handles the resolution of external
identifiers and URI references through XML catalogs. This
component supports XML catalogs defined by the

OASIS XML Catalogs Specification. It encapsulates the 
XML Commons resolver. 
An instance of this class may be registered on the parser 
as a SAX entity resolver, as a DOM LSResourceResolver or 
as an XNI entity resolver by setting the property
(http://apache.org/xml/properties/internal/entity-resolver).
It is intended that this class may be used standalone to perform 
catalog resolution outside of a parsing context. It may be shared
between several parsers and the application.
Author:
Michael Glavassevich, IBM
Version:
$Id: XMLCatalogResolver.java 699892 2008-09-28 21:08:27Z mrglavas $/**
 * <p>The catalog resolver handles the resolution of external
 * identifiers and URI references through XML catalogs. This
 * component supports XML catalogs defined by the
 * <a href="http://www.oasis-open.org/committees/entity/spec.html">
 * OASIS XML Catalogs Specification</a>. It encapsulates the 
 * <a href="http://xml.apache.org/commons/">XML Commons</a> resolver. 
 * An instance of this class may be registered on the parser 
 * as a SAX entity resolver, as a DOM LSResourceResolver or 
 * as an XNI entity resolver by setting the property
 * (http://apache.org/xml/properties/internal/entity-resolver).</p>
 * 
 * <p>It is intended that this class may be used standalone to perform 
 * catalog resolution outside of a parsing context. It may be shared
 * between several parsers and the application.</p>
 *
 * @author Michael Glavassevich, IBM
 *
 * @version $Id: XMLCatalogResolver.java 699892 2008-09-28 21:08:27Z mrglavas $
 */
public class XMLCatalogResolver 
    implements XMLEntityResolver, EntityResolver2, LSResourceResolver {
    
    
Internal catalog manager for Apache catalogs. /** Internal catalog manager for Apache catalogs. **/
    private CatalogManager fResolverCatalogManager = null;
    
    
Internal catalog structure. /** Internal catalog structure. **/
    private Catalog fCatalog = null;
	
    
An array of catalog URIs. /** An array of catalog URIs. **/
    private String [] fCatalogsList = null;

    
Indicates whether the list of catalogs has
changed since it was processed.
/** 
     * Indicates whether the list of catalogs has
     * changed since it was processed.
     */
    private boolean fCatalogsChanged = true;
    
    
Application specified prefer public setting. /** Application specified prefer public setting. **/
    private boolean fPreferPublic = true;
    
    
Indicates whether the application desires that 
the parser or some other component performing catalog
resolution should use the literal system identifier
instead of the expanded system identifier.
/** 
     * Indicates whether the application desires that 
     * the parser or some other component performing catalog
     * resolution should use the literal system identifier
     * instead of the expanded system identifier.
     */
    private boolean fUseLiteralSystemId = true;
    
    
Constructs a catalog resolver with a default configuration.
/**
     * <p>Constructs a catalog resolver with a default configuration.</p>
     */
    public XMLCatalogResolver () {
    	this(null, true);
    }
    
    
Constructs a catalog resolver with the given
list of entry files.
Params:
catalogs – an ordered array list of absolute URIs/**
     * <p>Constructs a catalog resolver with the given
     * list of entry files.</p>
     * 
     * @param catalogs an ordered array list of absolute URIs
     */
    public XMLCatalogResolver (String [] catalogs) {
    	this(catalogs, true);
    }
    
    
Constructs a catalog resolver with the given
list of entry files and the preference for whether
system or public matches are preferred.
Params:
catalogs – an ordered array list of absolute URIs
preferPublic – the prefer public setting/**
     * <p>Constructs a catalog resolver with the given
     * list of entry files and the preference for whether
     * system or public matches are preferred.</p>
     * 
     * @param catalogs an ordered array list of absolute URIs
     * @param preferPublic the prefer public setting
     */
    public XMLCatalogResolver (String [] catalogs, boolean preferPublic) {
        init(catalogs, preferPublic);
    }
    
    
Returns the initial list of catalog entry files.
Returns:
the initial list of catalog entry files/**
     * <p>Returns the initial list of catalog entry files.</p>
     * 
     * @return the initial list of catalog entry files
     */
    public final synchronized String [] getCatalogList () {
        return (fCatalogsList != null) 
            ? (String[]) fCatalogsList.clone() : null;
    }

    
Sets the initial list of catalog entry files.
If there were any catalog mappings cached from 
the previous list they will be replaced by catalog 
mappings from the new list the next time the catalog
is queried.
Params:
catalogs – an ordered array list of absolute URIs/**
     * <p>Sets the initial list of catalog entry files.
     * If there were any catalog mappings cached from 
     * the previous list they will be replaced by catalog 
     * mappings from the new list the next time the catalog
     * is queried.</p>
     * 
     * @param catalogs an ordered array list of absolute URIs 
     */
    public final synchronized void setCatalogList (String [] catalogs) {
        fCatalogsChanged = true;
        fCatalogsList = (catalogs != null)
            ? (String[]) catalogs.clone() : null;
    }
    
    
Forces the cache of catalog mappings to be cleared.
/**
     * <p>Forces the cache of catalog mappings to be cleared.</p>
     */
    public final synchronized void clear () {
        fCatalog = null;
    }
    
    
Returns the preference for whether system or public
matches are preferred. This is used in the absence
of any occurrence of the prefer attribute
on the catalog entry of a catalog. If this
property has not yet been explicitly set its value is
true.
Returns:
the prefer public setting/**
     * <p>Returns the preference for whether system or public
     * matches are preferred. This is used in the absence
     * of any occurrence of the <code>prefer</code> attribute
     * on the <code>catalog</code> entry of a catalog. If this
     * property has not yet been explicitly set its value is
     * <code>true</code>.</p>
     * 
     * @return the prefer public setting
     */
    public final boolean getPreferPublic () {
        return fPreferPublic;
    }
    
    
Sets the preference for whether system or public
matches are preferred. This is used in the absence
of any occurrence of the prefer attribute
on the catalog entry of a catalog.
Params:
preferPublic – the prefer public setting/**
     * <p>Sets the preference for whether system or public
     * matches are preferred. This is used in the absence
     * of any occurrence of the <code>prefer</code> attribute
     * on the <code>catalog</code> entry of a catalog.</p>
     * 
     * @param preferPublic the prefer public setting
     */
    public final void setPreferPublic (boolean preferPublic) {
        fPreferPublic = preferPublic;
        fResolverCatalogManager.setPreferPublic(preferPublic);
    }
    
    
Returns the preference for whether the literal system 
identifier should be used when resolving system 
identifiers when both it and the expanded system 
identifier are available. If this property has not yet 
been explicitly set its value is true.
See Also:
setUseLiteralSystemId
Returns:
the preference for using literal system identifiers
for catalog resolution/**
     * <p>Returns the preference for whether the literal system 
     * identifier should be used when resolving system 
     * identifiers when both it and the expanded system 
     * identifier are available. If this property has not yet 
     * been explicitly set its value is <code>true</code>.</p>
     * 
     * @return the preference for using literal system identifiers
     * for catalog resolution
     * 
     * @see #setUseLiteralSystemId
     */
    public final boolean getUseLiteralSystemId () {
        return fUseLiteralSystemId;
    }
    
    
Sets the preference for whether the literal system 
identifier should be used when resolving system 
identifiers when both it and the expanded system 
identifier are available.
The literal system identifier is the URI as it was
provided before absolutization. It may be embedded within 
an entity. It may be provided externally or it may be the 
result of redirection. For example, redirection may 
have come from the protocol level through HTTP or from 
an application's entity resolver.
The expanded system identifier is an absolute URI 
which is the result of resolving the literal system 
identifier against a base URI.
Params:
useLiteralSystemId – the preference for using 
literal system identifiers for catalog resolution/**
     * <p>Sets the preference for whether the literal system 
     * identifier should be used when resolving system 
     * identifiers when both it and the expanded system 
     * identifier are available.</p>
     * 
     * <p>The literal system identifier is the URI as it was
     * provided before absolutization. It may be embedded within 
     * an entity. It may be provided externally or it may be the 
     * result of redirection. For example, redirection may 
     * have come from the protocol level through HTTP or from 
     * an application's entity resolver.</p>
     * 
     * <p>The expanded system identifier is an absolute URI 
     * which is the result of resolving the literal system 
     * identifier against a base URI.</p>
     * 
     * @param useLiteralSystemId the preference for using 
     * literal system identifiers for catalog resolution
     */
    public final void setUseLiteralSystemId (boolean useLiteralSystemId) {
        fUseLiteralSystemId = useLiteralSystemId;
    }
    
    
Resolves an external entity. If the entity cannot be
resolved, this method should return null. This
method returns an input source if an entry was found in the
catalog for the given external identifier. It should be
overridden if other behaviour is required.
Params:
publicId – the public identifier, or null if none was supplied
systemId – the system identifier
Throws:
SAXException – any SAX exception, possibly wrapping another exception
IOException – thrown if some i/o error occurs/**
     * <p>Resolves an external entity. If the entity cannot be
     * resolved, this method should return <code>null</code>. This
     * method returns an input source if an entry was found in the
     * catalog for the given external identifier. It should be
     * overridden if other behaviour is required.</p>
     * 
     * @param publicId the public identifier, or <code>null</code> if none was supplied
     * @param systemId the system identifier
     * 
     * @throws SAXException any SAX exception, possibly wrapping another exception
     * @throws IOException thrown if some i/o error occurs
     */
    public InputSource resolveEntity(String publicId, String systemId)
    	 throws SAXException, IOException {
        
        String resolvedId = null;
        if (publicId != null && systemId != null) {
            resolvedId = resolvePublic(publicId, systemId);
        }
        else if (systemId != null) {
            resolvedId = resolveSystem(systemId);
        }
        
        if (resolvedId != null) {
            InputSource source = new InputSource(resolvedId);
            source.setPublicId(publicId);
            return source;
        }  
        return null;
    }
    
     
Resolves an external entity. If the entity cannot be
resolved, this method should return null. This
method returns an input source if an entry was found in the
catalog for the given external identifier. It should be
overridden if other behaviour is required.
Params:
name – the identifier of the external entity
publicId – the public identifier, or null if none was supplied
baseURI – the URI with respect to which relative systemIDs are interpreted.
systemId – the system identifier
Throws:
SAXException – any SAX exception, possibly wrapping another exception
IOException – thrown if some i/o error occurs/**
      * <p>Resolves an external entity. If the entity cannot be
      * resolved, this method should return <code>null</code>. This
      * method returns an input source if an entry was found in the
      * catalog for the given external identifier. It should be
      * overridden if other behaviour is required.</p>
      * 
      * @param name the identifier of the external entity 
      * @param publicId the public identifier, or <code>null</code> if none was supplied
      * @param baseURI the URI with respect to which relative systemIDs are interpreted.
      * @param systemId the system identifier
      * 
      * @throws SAXException any SAX exception, possibly wrapping another exception
      * @throws IOException thrown if some i/o error occurs
      */
     public InputSource resolveEntity(String name, String publicId, 
         String baseURI, String systemId) throws SAXException, IOException { 
        
         String resolvedId = null;
         
         if (!getUseLiteralSystemId() && baseURI != null) {
             // Attempt to resolve the system identifier against the base URI.
             try {
                 URI uri = new URI(new URI(baseURI), systemId);
                 systemId = uri.toString();
             }
             // Ignore the exception. Fallback to the literal system identifier.
             catch (URI.MalformedURIException ex) {}
         }
         
         if (publicId != null && systemId != null) {
             resolvedId = resolvePublic(publicId, systemId);
         }
         else if (systemId != null) {
             resolvedId = resolveSystem(systemId);
         }
        
         if (resolvedId != null) {
             InputSource source = new InputSource(resolvedId);
             source.setPublicId(publicId);
             return source;
         }  
         return null;
    }

     
Locates an external subset for documents which do not explicitly
provide one. This method always returns null. It
should be overrided if other behaviour is required.
Params:
name – the identifier of the document root element
baseURI – the document's base URI
Throws:
SAXException – any SAX exception, possibly wrapping another exception
IOException – thrown if some i/o error occurs/**
      * <p>Locates an external subset for documents which do not explicitly
      * provide one. This method always returns <code>null</code>. It
      * should be overrided if other behaviour is required.</p>
      * 
      * @param name the identifier of the document root element 
      * @param baseURI the document's base URI
      * 
      * @throws SAXException any SAX exception, possibly wrapping another exception
      * @throws IOException thrown if some i/o error occurs
      */
     public InputSource getExternalSubset(String name, String baseURI)
         throws SAXException, IOException {
         return null;
     }

    
Resolves a resource using the catalog. This method interprets that 
the namespace URI corresponds to uri entries in the catalog.
Where both a namespace and an external identifier exist, the namespace
takes precedence.
Params:
type – the type of the resource being resolved
namespaceURI – the namespace of the resource being resolved, 
or null if none was supplied
publicId – the public identifier of the resource being resolved,
or null if none was supplied
systemId – the system identifier of the resource being resolved,
or null if none was supplied
baseURI – the absolute base URI of the resource being parsed, 
or null if there is no base URI/** 
     * <p>Resolves a resource using the catalog. This method interprets that 
     * the namespace URI corresponds to uri entries in the catalog.
     * Where both a namespace and an external identifier exist, the namespace
     * takes precedence.</p>
     * 
     * @param type the type of the resource being resolved
     * @param namespaceURI the namespace of the resource being resolved, 
     * or <code>null</code> if none was supplied
     * @param publicId the public identifier of the resource being resolved,
     * or <code>null</code> if none was supplied
     * @param systemId the system identifier of the resource being resolved,
     * or <code>null</code> if none was supplied
     * @param baseURI the absolute base URI of the resource being parsed, 
     * or <code>null</code> if there is no base URI
     */
    public LSInput resolveResource(String type, String namespaceURI,
        String publicId, String systemId, String baseURI) {

        String resolvedId = null;
        
        try {
            // The namespace is useful for resolving namespace aware
            // grammars such as XML schema. Let it take precedence over
            // the external identifier if one exists.
            if (namespaceURI != null) {
                resolvedId = resolveURI(namespaceURI);
            }
            
            if (!getUseLiteralSystemId() && baseURI != null) {
                // Attempt to resolve the system identifier against the base URI.
                try {
                    URI uri = new URI(new URI(baseURI), systemId);
                    systemId = uri.toString();
                }
                // Ignore the exception. Fallback to the literal system identifier.
                catch (URI.MalformedURIException ex) {}
            }
        
            // Resolve against an external identifier if one exists. This
            // is useful for resolving DTD external subsets and other 
            // external entities. For XML schemas if there was no namespace 
            // mapping we might be able to resolve a system identifier 
            // specified as a location hint.
            if (resolvedId == null) {
                if (publicId != null && systemId != null) {
                    resolvedId = resolvePublic(publicId, systemId);
                }
                else if (systemId != null) {
                    resolvedId = resolveSystem(systemId);
                }
            }
        }
        // Ignore IOException. It cannot be thrown from this method.
        catch (IOException ex) {}
        
        if (resolvedId != null) {
            return new DOMInputImpl(publicId, resolvedId, baseURI);
        }  
        return null;
    }
    
    
    
Resolves an external entity. If the entity cannot be
resolved, this method should return null. This
method only calls resolveIdentifier and returns
an input source if an entry was found in the catalog. It
should be overridden if other behaviour is required.
Params:
resourceIdentifier – location of the XML resource to resolve
Throws:
XNIException – thrown on general error
IOException – thrown if some i/o error occurs/**
     * <p>Resolves an external entity. If the entity cannot be
     * resolved, this method should return <code>null</code>. This
     * method only calls <code>resolveIdentifier</code> and returns
     * an input source if an entry was found in the catalog. It
     * should be overridden if other behaviour is required.</p>
     *
     * @param resourceIdentifier location of the XML resource to resolve
     *
     * @throws XNIException thrown on general error
     * @throws IOException thrown if some i/o error occurs 
     */
    public XMLInputSource resolveEntity(XMLResourceIdentifier resourceIdentifier)
        throws XNIException, IOException {

        String resolvedId = resolveIdentifier(resourceIdentifier);
        if (resolvedId != null) {
            return new XMLInputSource(resourceIdentifier.getPublicId(), 
                                      resolvedId, 
                                      resourceIdentifier.getBaseSystemId());
        }
        return null;
    }
	
    
Resolves an identifier using the catalog. This method interprets that 
the namespace of the identifier corresponds to uri entries in the catalog.
Where both a namespace and an external identifier exist, the namespace
takes precedence.
Params:
resourceIdentifier – the identifier to resolve
Throws:
XNIException – thrown on general error
IOException – thrown if some i/o error occurs/** 
     * <p>Resolves an identifier using the catalog. This method interprets that 
     * the namespace of the identifier corresponds to uri entries in the catalog.
     * Where both a namespace and an external identifier exist, the namespace
     * takes precedence.</p>
     * 
     * @param resourceIdentifier the identifier to resolve
     * 
     * @throws XNIException thrown on general error
     * @throws IOException thrown if some i/o error occurs
     */
    public String resolveIdentifier(XMLResourceIdentifier resourceIdentifier)
        throws IOException, XNIException {
        
        String resolvedId = null;

        // The namespace is useful for resolving namespace aware
        // grammars such as XML schema. Let it take precedence over
        // the external identifier if one exists.
        String namespace = resourceIdentifier.getNamespace();
        if (namespace != null) {
            resolvedId = resolveURI(namespace);
        }
        
        // Resolve against an external identifier if one exists. This
        // is useful for resolving DTD external subsets and other 
        // external entities. For XML schemas if there was no namespace 
        // mapping we might be able to resolve a system identifier 
        // specified as a location hint.
        if (resolvedId == null) {
            String publicId = resourceIdentifier.getPublicId();
            String systemId = getUseLiteralSystemId() 
                ? resourceIdentifier.getLiteralSystemId()
                : resourceIdentifier.getExpandedSystemId();
            if (publicId != null && systemId != null) {
                resolvedId = resolvePublic(publicId, systemId);
            }
            else if (systemId != null) {
                resolvedId = resolveSystem(systemId);
            }
        }
        return resolvedId;
    }
    
    
Returns the URI mapping in the catalog for the given
external identifier or null if no mapping
exists. If the system identifier is an URN in the
publicid namespace it is converted into
a public identifier by URN "unwrapping" as specified
in the XML Catalogs specification.
Params:
systemId – the system identifier to locate in the catalog
Throws:
IOException – if an i/o error occurred while reading
the catalog
Returns:
the mapped URI or null if no mapping
was found in the catalog/**
     * <p>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.</p>
     * 
     * @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;
    }
    
    
Returns the URI mapping in the catalog for the given
external identifier or null if no mapping
exists. Public identifiers are normalized before
comparison.
Params:
publicId – the public identifier to locate in the catalog
systemId – the system identifier to locate in the catalog
Throws:
IOException – if an i/o error occurred while reading
the catalog
Returns:
the mapped URI or null if no mapping
was found in the catalog/**
     * <p>Returns the URI mapping in the catalog for the given
     * external identifier or <code>null</code> if no mapping
     * exists. Public identifiers are normalized before
     * comparison.</p>
     * 
     * @param publicId the public identifier to locate in the catalog
     * @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 resolvePublic (String publicId, String systemId) 
        throws IOException {

        if (fCatalogsChanged) {
            parseCatalogs();
            fCatalogsChanged = false;
        }
        return (fCatalog != null) 
            ? fCatalog.resolvePublic(publicId, systemId) : null;
    }
    
    
Returns the URI mapping in the catalog for the given URI
reference or null if no mapping exists. 
URI comparison is case sensitive. If the URI reference 
is an URN in the publicid namespace 
it is converted into a public identifier by URN "unwrapping" 
as specified in the XML Catalogs specification and then
resolution is performed following the semantics of 
external identifier resolution.
Params:
uri – the URI to locate in the catalog
Throws:
IOException – if an i/o error occurred while reading
the catalog
Returns:
the mapped URI or null if no mapping
was found in the catalog/**
     * <p>Returns the URI mapping in the catalog for the given URI
     * reference or <code>null</code> if no mapping exists. 
     * URI comparison is case sensitive. If the URI reference 
     * 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 and then
     * resolution is performed following the semantics of 
     * external identifier resolution.</p>
     * 
     * @param uri the URI 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 resolveURI (String uri) 
        throws IOException {

        if (fCatalogsChanged) {
            parseCatalogs();
            fCatalogsChanged = false;
        }
        return (fCatalog != null)
            ? fCatalog.resolveURI(uri) : null;
    }
    
    
Initialization. Create a CatalogManager and set all 
the properties upfront. This prevents JVM wide system properties 
or a property file somewhere in the environment from affecting 
the behaviour of this catalog resolver.
/**
     * Initialization. Create a CatalogManager and set all 
     * the properties upfront. This prevents JVM wide system properties 
     * or a property file somewhere in the environment from affecting 
     * the behaviour of this catalog resolver.
     */
    private void init (String [] catalogs, boolean preferPublic) {
        fCatalogsList = (catalogs != null) ? (String[]) catalogs.clone() : null;
        fPreferPublic = preferPublic;
        fResolverCatalogManager = new CatalogManager();
        fResolverCatalogManager.setAllowOasisXMLCatalogPI(false);
        fResolverCatalogManager.setCatalogClassName("org.apache.xml.resolver.Catalog");
        fResolverCatalogManager.setCatalogFiles("");
        fResolverCatalogManager.setIgnoreMissingProperties(true);
        fResolverCatalogManager.setPreferPublic(fPreferPublic);
        fResolverCatalogManager.setRelativeCatalogs(false);
        fResolverCatalogManager.setUseStaticCatalog(false);
        fResolverCatalogManager.setVerbosity(0);
    }
    
    
Instruct the Catalog to parse each of the  
catalogs in the list. Only the first catalog will actually be 
parsed immediately. The others will be queued and read if 
they are needed later.
/**
     * Instruct the <code>Catalog</code> to parse each of the  
     * catalogs in the list. Only the first catalog will actually be 
     * parsed immediately. The others will be queued and read if 
     * they are needed later.
     */
    private void parseCatalogs () throws IOException {
        if (fCatalogsList != null) {
            fCatalog = new Catalog(fResolverCatalogManager);
            attachReaderToCatalog(fCatalog);
            for (int i = 0; i < fCatalogsList.length; ++i) {
                String catalog = fCatalogsList[i];
                if (catalog != null && catalog.length() > 0) {
                    fCatalog.parseCatalog(catalog);
                }
            }
        }
        else {
            fCatalog = null;
        }
    }
    
    
Attaches the reader to the catalog.
/**
     * Attaches the reader to the catalog.
     */
    private void attachReaderToCatalog (Catalog catalog) {

        SAXParserFactory spf = new SAXParserFactoryImpl();
        spf.setNamespaceAware(true);
        spf.setValidating(false);

        SAXCatalogReader saxReader = new SAXCatalogReader(spf);
        saxReader.setCatalogParser(OASISXMLCatalogReader.namespaceName, "catalog", 
            "org.apache.xml.resolver.readers.OASISXMLCatalogReader");
        catalog.addReader("application/xml", saxReader);
    }
}