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
018package 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 */
028public interface JexlPropertyGet {
029    /**
030     * Method used to get the property value of an object.
031     * 
032     * @param obj the object to get the property value from.
033     * @return the property value.
034     * @throws Exception on any error.
035     */
036    Object invoke(Object obj) throws Exception;
037
038    /**
039     * Attempts to reuse this JexlPropertyGet, checking that it is compatible with
040     * the actual set of arguments.
041     * @param obj the object to invoke the property get upon
042     * @param key the property key to get
043     * @return the result of the method invocation that should be checked by tryFailed to determine if it succeeded
044     * or failed.
045     */
046    Object tryInvoke(Object obj, Object key);
047
048    /**
049     * Checks whether a tryInvoke failed or not.
050     * @param rval the value returned by tryInvoke
051     * @return true if tryInvoke failed, false otherwise
052     */
053    boolean tryFailed(Object rval);
054
055    /**
056     * Specifies if this JexlPropertyGet is cacheable and able to be reused for
057     * this class of object it was returned for.
058     *
059     * @return true if can be reused for this class, false if not
060     */
061    boolean isCacheable();
062}