    001    /*
    002     * Licensed to the Apache Software Foundation (ASF) under one or more
    003     * contributor license agreements.  See the NOTICE file distributed with
    004     * this work for additional information regarding copyright ownership.
    005     * The ASF licenses this file to You under the Apache License, Version 2.0
    006     * (the "License"); you may not use this file except in compliance with
    007     * the License.  You may obtain a copy of the License at
    008     *
    009     *      http://www.apache.org/licenses/LICENSE-2.0
    010     *
    011     * Unless required by applicable law or agreed to in writing, software
    012     * distributed under the License is distributed on an "AS IS" BASIS,
    013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014     * See the License for the specific language governing permissions and
    015     * limitations under the License.
    016     */
    017
    018    package org.apache.commons.jexl2.introspection;
    019
    020    /**
    021     * Interface for getting values that appear to be properties.
    022     * Ex.
    023     * <code>
    024     * ${foo.bar}
    025     * </code>
    026     * @since 1.0
    027     * @author <a href="mailto:geirm@optonline.net">Geir Magnusson Jr.</a>
    028     * @version $Id: JexlPropertyGet.java 889760 2009-12-11 18:42:49Z sebb $
    029     */
    030    public interface JexlPropertyGet {
    031        /**
    032         * Method used to get the property value of an object.
    033         *
    034         * @param obj the object to get the property value from.
    035         * @return the property value.
    036         * @throws Exception on any error.
    037         */
    038        Object invoke(Object obj) throws Exception;
    039
    040        /**
    041         * Attempts to reuse this JexlPropertyGet, checking that it is compatible with
    042         * the actual set of arguments.
    043         * @param obj the object to invoke the property get upon
    044         * @param key the property key to get
    045         * @return the result of the method invocation that should be checked by tryFailed to determine if it succeeded
    046         * or failed.
    047         */
    048        Object tryInvoke(Object obj, Object key);
    049
    050        /**
    051         * Checks whether a tryInvoke failed or not.
    052         * @param rval the value returned by tryInvoke
    053         * @return true if tryInvoke failed, false otherwise
    054         */
    055        boolean tryFailed(Object rval);
    056
    057        /**
    058         * Specifies if this JexlPropertyGet is cacheable and able to be reused for
    059         * this class of object it was returned for.
    060         *
    061         * @return true if can be reused for this class, false if not
    062         */
    063        boolean isCacheable();
    064    }