configuration/xml/src/main/java/org/apache/commons/chain2/config/xml/ConfigRegisterRule.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.Chain;
import org.apache.commons.chain2.Command;
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.Command} to be registered with the next-to-top
 * element on the Digester stack (if it is a {@link org.apache.commons.chain2.Catalog} or {@link org.apache.commons.chain2.Chain}).
 * To be registered with a {@link org.apache.commons.chain2.Catalog}, the top-most element must contain
 * a value for the specified attribute that contains the name under which
 * it should be registered.</p>
 *
 */
class ConfigRegisterRule 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
     */
    public ConfigRegisterRule(String nameAttribute) {
        this.nameAttribute = nameAttribute;
    }

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

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

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

    /**
     * <p>Register the top {@link org.apache.commons.chain2.Command} if appropriate.</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 {
        // Is the top object a Command?
        Object top = getDigester().peek(0);
        if ((top == null)
            || !(top instanceof Command)) {
            return;
        }

        /* All commands can consume a generic context. Here we depend on
         * the configuration being correct because the rule binding is
         * dynamic. */
        Command<Object, Object, Map<Object, Object>> command =
                (Command<Object, Object, Map<Object, Object>>) top;

        // Is the next object a Catalog or a Chain?
        Object next = getDigester().peek(1);
        if (next == null) {
            return;
        }

        // Register the top element appropriately
        if (next instanceof Catalog) {
            String nameValue = attributes.getValue(nameAttribute);
            if (nameValue != null) {
                /* We are dynamically building a catalog and assigning
                 * generics to the most base types possible. */
                Catalog<Object, Object, Map<Object, Object>> catalog =
                        (Catalog<Object, Object, Map<Object, Object>>) next;
                catalog.addCommand(nameValue, command);
            }
        } else if (next instanceof Chain) {
            /* Like above - the chain is being dynamically generated,
             * so we can add a generic context signature at compile-time. */
            Chain<Object, Object, Map<Object, Object>> chain = (Chain<Object, Object, Map<Object, Object>>) next;
            chain.addCommand(command);
        }
    }

}