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 */
017package org.apache.commons.configuration2.beanutils;
018
019import java.util.Collection;
020import java.util.Map;
021
022/**
023 * <p>
024 * Definition of an interface for declaring a bean in a configuration file.
025 * </p>
026 * <p>
027 * Commons Configurations allows to define beans (i.e. simple Java objects) in configuration files, which can be created
028 * at runtime. This is especially useful if you program against interfaces and want to define the concrete
029 * implementation class is a configuration file.
030 * </p>
031 * <p>
032 * This interface defines methods for retrieving all information about a bean that should be created from a
033 * configuration file, e.g. the bean's properties or the factory to use for creating the instance. With different
034 * implementations different &quot;layouts&quot; of bean declarations can be supported. For instance if an XML
035 * configuration file is used, all features of XML (e.g. attributes, nested elements) can be used to define the bean. In
036 * a properties file the declaration format is more limited. The purpose of this interface is to abstract from the
037 * concrete declaration format.
038 * </p>
039 *
040 * @since 1.3
041 */
042public interface BeanDeclaration {
043
044    /**
045     * Gets the name of the bean class, from which an instance is to be created. This value must be defined unless a
046     * default class is provided for the bean creation operation.
047     *
048     * @return the name of the bean class
049     */
050    String getBeanClassName();
051
052    /**
053     * Gets the name of the {@code BeanFactory} that should be used for creating the bean instance. This can be
054     * <b>null</b>, then a default factory will be used.
055     *
056     * @return the name of the bean factory
057     */
058    String getBeanFactoryName();
059
060    /**
061     * Gets an arbitrary object that will be passed to the bean factory. Its meaning is not further
062     * specified. The purpose of this additional parameter is to support a further configuration of the bean factory that
063     * can be placed directly at the bean declaration.
064     *
065     * @return a parameter for the bean factory
066     */
067    Object getBeanFactoryParameter();
068
069    /**
070     * Gets a map with properties that should be initialized on the newly created bean. The map's keys are the names of
071     * the properties; the corresponding values are the properties' values. The return value can be <b>null</b> if no
072     * properties should be set.
073     *
074     * @return a map with properties to be initialized
075     */
076    Map<String, Object> getBeanProperties();
077
078    /**
079     * Gets a collection with constructor arguments. This data is used to determine the constructor of the bean class to
080     * be invoked. The values of the arguments are passed to the constructor. An implementation can return <b>null</b> or an
081     * empty collection; then the standard constructor of the bean class is called.
082     *
083     * @return a collection with the arguments to be passed to the bean class's constructor
084     */
085    Collection<ConstructorArg> getConstructorArgs();
086
087    /**
088     * Gets a map with declarations for beans that should be set as properties of the newly created bean. This allows for
089     * complex initialization scenarios: a bean for a bean that contains complex properties (e.g. other beans) can have
090     * nested declarations for defining these complex properties. The returned map's key are the names of the properties to
091     * initialize. The values are either {@code BeanDeclaration} implementations or collections thereof. They will be
092     * treated like this declaration (in a recursive manner), and the resulting beans are assigned to the corresponding
093     * properties.
094     *
095     * @return a map with nested bean declarations
096     */
097    Map<String, Object> getNestedBeanDeclarations();
098}