core/src/main/java/org/apache/commons/digester3/xmlrules/IncludeRule.java

package org.apache.commons.digester3.xmlrules;

/*
 * 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.
 */

import java.net.MalformedURLException;
import java.net.URL;
import java.util.Set;

import org.apache.commons.digester3.Rule;
import org.apache.commons.digester3.binder.RulesBinder;
import org.apache.commons.digester3.binder.RulesModule;
import org.xml.sax.Attributes;

/**
 * A rule for including one rules XML file within another. Included files behave as if they are 'macro-expanded' within
 * the includer. This means that the values of the pattern stack are prefixed to every pattern in the included rules.
 * <p>
 * This rule will detect 'circular' includes, which would result in infinite recursion. It throws a
 * CircularIncludeException when a cycle is detected, which will terminate the parse.
 */
final class IncludeRule
    extends Rule
{

    private static final String CLASSPATH_URL_PREFIX = "classpath:";

    private final WithMemoryRulesBinder memoryRulesBinder;

    private final RulesBinder targetRulesBinder;

    public IncludeRule( final WithMemoryRulesBinder memoryRulesBinder, final RulesBinder targetRulesBinder )
    {
        this.memoryRulesBinder = memoryRulesBinder;
        this.targetRulesBinder = targetRulesBinder;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void begin( final String namespace, final String name, final Attributes attributes )
        throws Exception
    {
        // The path attribute gives the URI to another digester rules xml file
        final String fileName = attributes.getValue( "url" );
        if ( fileName != null && !fileName.isEmpty() )
        {
            final URL xmlRulesResource;

            if ( fileName.startsWith( CLASSPATH_URL_PREFIX ) )
            {
                String path = fileName.substring( CLASSPATH_URL_PREFIX.length() );
                if ( '/' == path.charAt( 0 ) )
                {
                    path = path.substring( 1 );
                }
                xmlRulesResource = this.targetRulesBinder.getContextClassLoader().getResource( path );
                if ( xmlRulesResource == null )
                {
                    targetRulesBinder.addError( "Resource '%s' not found, please make sure it is in the classpath",
                                                path );
                    return;
                }
            }
            else
            {
                try
                {
                    xmlRulesResource = new URL( fileName );
                }
                catch ( final MalformedURLException e )
                {
                    targetRulesBinder.addError( "An error occurred while inculing file from '%s': %s", fileName,
                                                e.getMessage() );
                    return;
                }
            }

            final Set<String> includedFiles = memoryRulesBinder.getIncludedFiles();
            final String xmlRulesResourceString = xmlRulesResource.toString();
            if ( includedFiles.add( xmlRulesResourceString ) )
            {
                try
                {
                    install( new FromXmlRulesModule()
                    {

                        @Override
                        protected void loadRules()
                        {
                            loadXMLRules( xmlRulesResource );
                        }

                    } );
                }
                finally
                {
                    includedFiles.remove( xmlRulesResourceString );
                }
            }
            else
            {
                targetRulesBinder.addError( "Circular file inclusion detected for XML rules: %s", xmlRulesResource );
            }
        }

        // The class attribute gives the name of a class that implements
        // the DigesterRulesSource interface
        final String className = attributes.getValue( "class" );
        if ( className != null && !className.isEmpty() )
        {
            try
            {
                final Class<?> cls = Class.forName( className );
                if ( !RulesModule.class.isAssignableFrom( cls ) )
                {
                    targetRulesBinder.addError( "Class '%s' if not a '%s' implementation", className,
                                                RulesModule.class.getName() );
                    return;
                }

                final RulesModule rulesSource = (RulesModule) cls.newInstance();

                install( rulesSource );
            }
            catch ( final Exception e )
            {
                targetRulesBinder.addError( "Impossible to include programmatic rules from class '%s': %s", className,
                                            e.getMessage() );
            }
        }
    }

    private void install( final RulesModule rulesModule )
    {
        // that's an hack, shall not be taken in consideration!!! :)
        rulesModule.configure( new PrefixedRulesBinder( targetRulesBinder,
                                                        memoryRulesBinder.getPatternStack().toString() ) );
    }

}