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.configuration.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 an also
036 * passed in {@link BeanDeclaration} 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 * @version $Id: BeanFactory.java 1208757 2011-11-30 20:38:15Z oheger $
047 */
048public interface BeanFactory
049{
050    /**
051     * Returns a bean instance for the given class. The bean will be initialized
052     * from the specified bean declaration object. It is up to a concrete
053     * implementation how the bean will be created and initialized.
054     *
055     * @param beanClass the class for the bean
056     * @param data the bean declaration object containing all data about the
057     * bean to be created
058     * @param param an additional parameter that may be passed by calling code;
059     * it is up to a concrete implementation how this parameter is evaluated
060     * @return the new bean instance (should not be <b>null</b>)
061     * @throws Exception if an error occurs (the helper classes for creating
062     * beans will catch this unspecific exception and wrap it in a configuration
063     * exception)
064     */
065    Object createBean(Class<?> beanClass, BeanDeclaration data, Object param)
066            throws Exception;
067
068    /**
069     * Returns the default bean class of this bean factory. If an implementation
070     * here returns a non <b>null</b> value, bean declarations using this
071     * factory do not need to provide the name of the bean class. In such a case
072     * an instance of the default class will be created.
073     *
074     * @return the default class of this factory or <b>null</b> if there is
075     * none
076     */
077    Class<?> getDefaultBeanClass();
078}