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
025 * called <em>bean factories</em>. This additional level of indirection
026 * provides for high flexibility in the creation process. For instance one
027 * implementation of this interface could be very simple and create a new
028 * instance of the specified class for each invocation. A different
029 * implementation could cache already created beans and ensure that always the
030 * same bean of the given class will be returned - this would be an easy mean
031 * for creating singleton objects.
032 * </p>
033 * <p>
034 * The interface itself is quite simple. There is a single method for creating a
035 * bean of a given class. All necessary parameters are obtained from a
036 * passed in {@link BeanCreationContext} object. It is also possible
037 * (but optional) for a bean factory to declare the default class of the bean it
038 * creates. Then it is not necessary to specify a bean class in the bean
039 * declaration.
040 * </p>
041 *
042 * @since 1.3
043 */
044public interface BeanFactory
045{
046    /**
047     * Returns a bean instance for the given context object. All information
048     * about the bean to be created are contained in the provided
049     * {@code BeanCreationContext} object. This includes a
050     * {@link BeanDeclaration} defining the properties of the bean. It is up to
051     * a concrete implementation how the bean is created and initialized.
052     *
053     * @param bcc the context object for the bean to be created
054     * @return the new bean instance (should not be <b>null</b>)
055     * @throws Exception if an error occurs (the helper classes for creating
056     *         beans will catch this generic exception and wrap it in a
057     *         configuration exception)
058     */
059    Object createBean(BeanCreationContext bcc) throws Exception;
060
061    /**
062     * Returns the default bean class of this bean factory. If an implementation
063     * here returns a non <b>null</b> value, bean declarations using this
064     * factory do not need to provide the name of the bean class. In such a case
065     * an instance of the default class will be created.
066     *
067     * @return the default class of this factory or <b>null</b> if there is
068     * none
069     */
070    Class<?> getDefaultBeanClass();
071}