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
019/**
020 * <p>
021 * Definition of an interface for bean factories.
022 * </p>
023 * <p>
024 * Beans defined in configuration files are not directly created, but by so called <em>bean factories</em>. This
025 * additional level of indirection provides for high flexibility in the creation process. For instance one
026 * implementation of this interface could be very simple and create a new instance of the specified class for each
027 * invocation. A different implementation could cache already created beans and ensure that always the same bean of the
028 * given class will be returned - this would be an easy mean for creating singleton objects.
029 * </p>
030 * <p>
031 * The interface itself is quite simple. There is a single method for creating a bean of a given class. All necessary
032 * parameters are obtained from a passed in {@link BeanCreationContext} object. It is also possible (but optional) for a
033 * bean factory to declare the default class of the bean it creates. Then it is not necessary to specify a bean class in
034 * the bean declaration.
035 * </p>
036 *
037 * @since 1.3
038 */
039public interface BeanFactory {
040
041    /**
042     * Creates a bean instance for the given context object. All information about the bean to be created are contained in
043     * the provided {@code BeanCreationContext} object. This includes a {@link BeanDeclaration} defining the properties of
044     * the bean. It is up to a concrete implementation how the bean is created and initialized.
045     *
046     * @param bcc the context object for the bean to be created
047     * @return the new bean instance (should not be <b>null</b>)
048     * @throws Exception if an error occurs (the helper classes for creating beans will catch this generic exception and
049     *         wrap it in a configuration exception)
050     */
051    Object createBean(BeanCreationContext bcc) throws Exception;
052
053    /**
054     * Gets the default bean class of this bean factory. If an implementation here returns a non <b>null</b> value, bean
055     * declarations using this factory do not need to provide the name of the bean class. In such a case an instance of the
056     * default class will be created.
057     *
058     * @return the default class of this factory or <b>null</b> if there is none
059     */
060    Class<?> getDefaultBeanClass();
061}