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     */
017    package 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     */
048    public 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    }