    001// Copyright 2023 The Apache Software Foundation
    002//
    003// Licensed under the Apache License, Version 2.0 (the "License");
    004// you may not use this file except in compliance with the License.
    005// You may obtain a copy of the License at
    006//
    007// http://www.apache.org/licenses/LICENSE-2.0
    008//
    009// Unless required by applicable law or agreed to in writing, software
    010// distributed under the License is distributed on an "AS IS" BASIS,
    011// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    012// See the License for the specific language governing permissions and
    013// limitations under the License.
    014
    015package org.apache.tapestry5.plastic;
    016
    017/**
    018 * <p>
    019 * Interface that can be implemented to provide access to field values based on their name.
    020 * Usually implemented with {@linkplain PlasticUtils#implementPropertyValueProvider(PlasticClass, java.util.Set)}.
    021 * </p>
    022 * <p>
    023 * The name of its abstract method is intended to avoid clashes with other existing methods
    024 * in the class.
    025 * </p>
    026 * @see PlasticUtils#implementPropertyValueProvider(PlasticClass, java.util.Set)
    027 * @since 5.8.4
    028 */
    029public interface PropertyValueProvider
    030{
    031    /**
    032     * Returns the value of a given field.
    033     * @param fieldName the field name.
    034     * @return the field value.
    035     */
    036    Object __propertyValueProvider__get(String fieldName);
    037
    038    /**
    039     * <p>
    040     * Returns the value of a given field in a given object if it belongs to a class
    041     * that implements {@linkplain PropertyValueProvider}. Otherwise, it throws an exception.
    042     * </p>
    043     * <p>
    044     * This is an utility method to avoid having to make casts very time you need to call
    045     * {@linkplain #__propertyValueProvider__get(String)}.
    046     * </p>
    047     * @param object an object.
    048     * @param fieldName the field name.
    049     * @return the field value.
    050     */
    051    static Object get(Object object, String fieldName)
    052    {
    053        if (object instanceof PropertyValueProvider)
    054        {
    055            return ((PropertyValueProvider) object).__propertyValueProvider__get(fieldName);
    056        }
    057        else
    058        {
    059            throw new RuntimeException("Class " + object.getClass().getName() + " doesn't implement " + PropertyValueProvider.class.getSimpleName());
    060        }
    061    }
    062
    063}