# EvaluatorFactoryFinder.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.synapse.commons.evaluators.config;

    import org.apache.axiom.om.OMElement;
    import org.apache.commons.logging.Log;
    import org.apache.commons.logging.LogFactory;
    import org.apache.synapse.commons.evaluators.Evaluator;
    import org.apache.synapse.commons.evaluators.EvaluatorConstants;
    import org.apache.synapse.commons.evaluators.EvaluatorException;

    import java.util.Map;
    import java.util.HashMap;

    /**
     * Factories for creating Evaluators are found using the evaluator name. This class stores
     * information about Evaluator Factories and their corresponding names. This is a Singleton class.
     */
    public class EvaluatorFactoryFinder {
        private static final Log log = LogFactory.getLog(EvaluatorFactoryFinder.class);

        private static final EvaluatorFactoryFinder finder = new EvaluatorFactoryFinder();

        private Map<String, EvaluatorFactory> factories = new HashMap<String, EvaluatorFactory>();

        private EvaluatorFactoryFinder() {
            factories.put(EvaluatorConstants.AND, new AndFactory());
            factories.put(EvaluatorConstants.OR, new OrFactory());
            factories.put(EvaluatorConstants.NOT, new NotFactory());
            factories.put(EvaluatorConstants.MATCH, new MatchFactory());
            factories.put(EvaluatorConstants.EQUAL, new EqualFactory());
        }

        /**
         * Return and instance of the <code>EvaluatorFactoryFinder</code>.
         * @return the EvaluatorFactoryFinder singleton
         */
        public static EvaluatorFactoryFinder getInstance() {
            return finder;
        }

        /**
         * Retun an <code>EvaluatorFactory</code> for a given Evaluator name.
         * @param name name of the Evaluator
         * @return an EvaluatorFactory
         */
        public EvaluatorFactory findEvaluatorFactory(String name) {
            return factories.get(name);
        }

        /**
         * Retun an <code>EvaluatorFactory</code> for a given Evaluator name.
         * @param elem A XML element containing the evaluator configuration
         * @return an Evaluator
         * @throws org.apache.synapse.commons.evaluators.EvaluatorException if it cannot find
         * a corresponding factory for creating an evaluator
         */
        public Evaluator getEvaluator(OMElement elem) throws EvaluatorException {

            EvaluatorFactory fac = findEvaluatorFactory(elem.getLocalName());
            if (fac == null) {
                handleException("Invalid configuration element: " + elem.getLocalName());
            } else {
                return fac.create(elem);
            }

            return null;
        }

        private void handleException(String message) throws EvaluatorException {
            log.error(message);
            throw new EvaluatorException(message);
        }
    }