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.jexl3.introspection;
019
020import org.apache.commons.jexl3.JexlException;
021
022/**
023 * Interface for getting values that appear to be properties.
024 * Ex.
025 * <code>
026 * ${foo.bar}
027 * </code>
028 *
029 * @since 1.0
030 */
031public interface JexlPropertyGet {
032    /**
033     * Method used to get the property value of an object.
034     *
035     * @param obj the object to get the property value from.
036     * @return the property value.
037     * @throws Exception on any error.
038     */
039    Object invoke(Object obj) throws Exception;
040
041    /**
042     * Attempts to reuse this JexlPropertyGet, checking that it is compatible with
043     * the actual set of arguments.
044     *
045     * @param obj the object to invoke the property get upon
046     * @param key the property key to get
047     * @return the result of the method invocation that should be checked by tryFailed to determine if it succeeded
048     * or failed.
049     * @throws JexlException.TryFailed if the underlying method was invoked but threw an exception
050     * ({@link java.lang.reflect.InvocationTargetException})
051     */
052    Object tryInvoke(Object obj, Object key) throws JexlException.TryFailed;
053
054    /**
055     * Checks whether a tryInvoke failed or not.
056     *
057     * @param rval the value returned by tryInvoke
058     * @return true if tryInvoke failed, false otherwise
059     */
060    boolean tryFailed(Object rval);
061
062    /**
063     * Specifies if this JexlPropertyGet is cacheable and able to be reused for
064     * this class of object it was returned for.
065     *
066     * @return true if can be reused for this class, false if not
067     */
068    boolean isCacheable();
069}