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 * @author <a
044 * href="http://commons.apache.org/configuration/team-list.html">Commons
045 * Configuration team</a>
046 */
047public interface BeanFactory
048{
049    /**
050     * Returns a bean instance for the given context object. All information
051     * about the bean to be created are contained in the provided
052     * {@code BeanCreationContext} object. This includes a
053     * {@link BeanDeclaration} defining the properties of the bean. It is up to
054     * a concrete implementation how the bean is created and initialized.
055     *
056     * @param bcc the context object for the bean to be created
057     * @return the new bean instance (should not be <b>null</b>)
058     * @throws Exception if an error occurs (the helper classes for creating
059     *         beans will catch this generic exception and wrap it in a
060     *         configuration exception)
061     */
062    Object createBean(BeanCreationContext bcc) throws Exception;
063
064    /**
065     * Returns the default bean class of this bean factory. If an implementation
066     * here returns a non <b>null</b> value, bean declarations using this
067     * factory do not need to provide the name of the bean class. In such a case
068     * an instance of the default class will be created.
069     *
070     * @return the default class of this factory or <b>null</b> if there is
071     * none
072     */
073    Class<?> getDefaultBeanClass();
074}