configuration/xml/src/main/java/org/apache/commons/chain2/config/xml/ConfigCatalogRule.java

/*
 * 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.commons.chain2.config.xml;

import org.apache.commons.chain2.Catalog;
import org.apache.commons.chain2.CatalogFactory;
import org.apache.commons.chain2.impl.CatalogFactoryBase;
import org.apache.commons.digester3.Rule;
import org.xml.sax.Attributes;

import java.util.Map;

/**
 * <p>Digester rule that will cause the top-most element on the Digester
 * stack (if it is a {@link org.apache.commons.chain2.Catalog} to be registered with the
 * {@link org.apache.commons.chain2.impl.CatalogFactoryBase} instance for our application.  If the attribute
 * specified to our constructor has a value, that will be used as the name
 * under which to register this {@link org.apache.commons.chain2.Catalog}.  Otherwise, this will
 * become the default {@link org.apache.commons.chain2.Catalog} for this application.</p>
 *
 * @version $Id: ConfigCatalogRule.java 1363305 2012-07-19 11:42:53Z simonetripodi $
 */
class ConfigCatalogRule extends Rule {

    // ----------------------------------------------------------- Constructors

    /**
     * <p>Construct a new instance of this rule that looks for an attribute
     * with the specified name.</p>
     *
     * @param nameAttribute Name of the attribute containing the name under
     *  which this command should be registered
     * @param catalogClass Name of the implementation class for newly
     *  created {@link org.apache.commons.chain2.Catalog} instances
     */
    public ConfigCatalogRule(String nameAttribute, String catalogClass) {
        this.nameAttribute = nameAttribute;
        this.catalogClass = catalogClass;
    }

    // ----------------------------------------------------- Instance Variables

    /**
     * <p>The fully qualified class name of a {@link org.apache.commons.chain2.Catalog} class to use for
     * instantiating new instances.</p>
     */
    private final String catalogClass;

    /**
     * <p>The name of the attribute under which we can retrieve the name
     * this catalog should be registered with (if any).</p>
     */
    private final String nameAttribute;

    // --------------------------------------------------------- Public Methods

    /**
     * <p>Retrieve or create a {@link org.apache.commons.chain2.Catalog} with the name specified by
     * the <code>nameAttribute</code> attribute, or the default {@link org.apache.commons.chain2.Catalog}
     * if there is no such attribute defined.  Push it onto the top of the
     * stack.</p>
     *
     * @param namespace the namespace URI of the matching element, or an
     *   empty string if the parser is not namespace aware or the element has
     *   no namespace
     * @param name the local name if the parser is namespace aware, or just
     *   the element name otherwise
     * @param attributes The attribute list of this element
     */
    @Override
    public void begin(String namespace, String name, Attributes attributes) throws Exception {
        // Retrieve any current Catalog with the specified name
        Catalog<Object, Object, Map<Object, Object>> catalog;
        CatalogFactory<Object, Object, Map<Object, Object>> factory = CatalogFactoryBase.getInstance();
        String nameValue = attributes.getValue(nameAttribute);
        if (nameValue == null) {
            catalog = factory.getCatalog();
        } else {
            catalog = factory.getCatalog(nameValue);
        }

        // Create and register a new Catalog instance if necessary
        if (catalog == null) {
            Class<?> clazz = getDigester().getClassLoader().loadClass(catalogClass);

            /* Convert catalog pulled from digester to default generic signature
             * with the assumption that the Catalog returned from digester will
             * comply with the the historic chain contract. */
            @SuppressWarnings("unchecked")
            Catalog<Object, Object, Map<Object, Object>> digesterCatalog =
                    (Catalog<Object, Object, Map<Object, Object>>) clazz.newInstance();

            catalog = digesterCatalog;

            if (nameValue == null) {

                factory.setCatalog(catalog);
            } else {
                factory.addCatalog(nameValue, catalog);
            }
        }

        // Push this Catalog onto the top of the stack
        getDigester().push(catalog);
    }

}