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