src/main/java/org/apache/commons/configuration2/beanutils/BeanDeclaration.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.configuration2.beanutils;

import java.util.Collection;
import java.util.Map;

/**
 * <p>
 * Definition of an interface for declaring a bean in a configuration file.
 * </p>
 * <p>
 * Commons Configurations allows to define beans (i.e. simple Java objects) in configuration files, which can be created
 * at runtime. This is especially useful if you program against interfaces and want to define the concrete
 * implementation class is a configuration file.
 * </p>
 * <p>
 * This interface defines methods for retrieving all information about a bean that should be created from a
 * configuration file, for example the bean's properties or the factory to use for creating the instance. With different
 * implementations different &quot;layouts&quot; of bean declarations can be supported. For instance if an XML
 * configuration file is used, all features of XML (for example attributes, nested elements) can be used to define the bean. In
 * a properties file the declaration format is more limited. The purpose of this interface is to abstract from the
 * concrete declaration format.
 * </p>
 *
 * @since 1.3
 */
public interface BeanDeclaration {

    /**
     * Gets the name of the bean class, from which an instance is to be created. This value must be defined unless a
     * default class is provided for the bean creation operation.
     *
     * @return the name of the bean class
     */
    String getBeanClassName();

    /**
     * Gets the name of the {@code BeanFactory} that should be used for creating the bean instance. This can be
     * <strong>null</strong>, then a default factory will be used.
     *
     * @return the name of the bean factory
     */
    String getBeanFactoryName();

    /**
     * Gets an arbitrary object that will be passed to the bean factory. Its meaning is not further
     * specified. The purpose of this additional parameter is to support a further configuration of the bean factory that
     * can be placed directly at the bean declaration.
     *
     * @return a parameter for the bean factory
     */
    Object getBeanFactoryParameter();

    /**
     * Gets a map with properties that should be initialized on the newly created bean. The map's keys are the names of
     * the properties; the corresponding values are the properties' values. The return value can be <strong>null</strong> if no
     * properties should be set.
     *
     * @return a map with properties to be initialized
     */
    Map<String, Object> getBeanProperties();

    /**
     * Gets a collection with constructor arguments. This data is used to determine the constructor of the bean class to
     * be invoked. The values of the arguments are passed to the constructor. An implementation can return <strong>null</strong> or an
     * empty collection; then the standard constructor of the bean class is called.
     *
     * @return a collection with the arguments to be passed to the bean class's constructor
     */
    Collection<ConstructorArg> getConstructorArgs();

    /**
     * Gets a map with declarations for beans that should be set as properties of the newly created bean. This allows for
     * complex initialization scenarios: a bean for a bean that contains complex properties (for example other beans) can have
     * nested declarations for defining these complex properties. The returned map's key are the names of the properties to
     * initialize. The values are either {@code BeanDeclaration} implementations or collections thereof. They will be
     * treated like this declaration (in a recursive manner), and the resulting beans are assigned to the corresponding
     * properties.
     *
     * @return a map with nested bean declarations
     */
    Map<String, Object> getNestedBeanDeclarations();
}