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 *      https://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    /**
034     * Method used to get the property value of an object.
035     *
036     * @param obj the object to get the property value from.
037     * @return the property value.
038     * @throws Exception on any error.
039     */
040    Object invoke(Object obj) throws Exception;
041
042    /**
043     * Specifies if this JexlPropertyGet is cacheable and able to be reused for
044     * this class of object it was returned for.
045     *
046     * @return true if can be reused for this class, false if not
047     */
048    boolean isCacheable();
049
050    /**
051     * Checks whether this JexlPropertyGet returns a constant.
052     *
053     * @return true if invoking this getter will always return the same value, false otherwise
054     */
055    default boolean isConstant() {
056        return false;
057    }
058
059    /**
060     * Checks whether a tryInvoke failed or not.
061     *
062     * @param rval the value returned by tryInvoke
063     * @return true if tryInvoke failed, false otherwise
064     */
065    boolean tryFailed(Object rval);
066
067    /**
068     * Attempts to reuse this JexlPropertyGet, checking that it is compatible with
069     * the actual set of arguments.
070     *
071     * @param obj the object to invoke the property get upon
072     * @param key the property key to get
073     * @return the result of the method invocation that should be checked by tryFailed to determine if it succeeded
074     * or failed.
075     * @throws JexlException.TryFailed if the underlying method was invoked but threw an exception
076     * ({@link java.lang.reflect.InvocationTargetException})
077     */
078    Object tryInvoke(Object obj, Object key) throws JexlException.TryFailed;
079}