src/main/java/org/apache/commons/configuration2/beanutils/CombinedBeanDeclaration.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
 *
 *     http://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.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * <p>
 * A special implementation of the {@code BeanDeclaration} interface which
 * allows combining multiple {@code BeanDeclaration} objects.
 * </p>
 * <p>
 * An instance of this class can be used if a bean is defined using multiple
 * sources. For instance, there can be one definition with default values and
 * one with actual values; if actual values are provided, they are used;
 * otherwise, the default values apply.
 * </p>
 * <p>
 * When constructing an instance an arbitrary number of child
 * {@code BeanDeclaration} objects can be specified. The implementations of the
 * {@code BeanDeclaration} methods implement a logical combination of the data
 * returned by these child declarations. The order in which child declarations
 * are added is relevant; first entries take precedence over later ones. The
 * comments of the single methods explain in which way a combination of the
 * child declarations is built.
 * </p>
 *
 * @version $Id$
 * @since 2.0
 */
public class CombinedBeanDeclaration implements BeanDeclaration
{
    /** A list with the child declarations. */
    private final List<BeanDeclaration> childDeclarations;

    /**
     * Creates a new instance of {@code CombinedBeanDeclaration} and initializes
     * it with the given child declarations.
     *
     * @param decl the child declarations
     * @throws NullPointerException if the array with child declarations is
     *         <b>null</b>
     */
    public CombinedBeanDeclaration(BeanDeclaration... decl)
    {
        childDeclarations = new ArrayList<BeanDeclaration>(Arrays.asList(decl));
    }

    /**
     * {@inheritDoc} This implementation iterates over the list of child
     * declarations and asks them for a bean factory name. The first
     * non-<b>null</b> value is returned. If none of the child declarations have
     * a defined bean factory name, result is <b>null</b>.
     */
    @Override
    public String getBeanFactoryName()
    {
        for (BeanDeclaration d : childDeclarations)
        {
            String factoryName = d.getBeanFactoryName();
            if (factoryName != null)
            {
                return factoryName;
            }
        }
        return null;
    }

    /**
     * {@inheritDoc} This implementation iterates over the list of child
     * declarations and asks them for a bean factory parameter. The first
     * non-<b>null</b> value is returned. If none of the child declarations have
     * a defined bean factory parameter, result is <b>null</b>.
     */
    @Override
    public Object getBeanFactoryParameter()
    {
        for (BeanDeclaration d : childDeclarations)
        {
            Object factoryParam = d.getBeanFactoryParameter();
            if (factoryParam != null)
            {
                return factoryParam;
            }
        }
        return null;
    }

    /**
     * {@inheritDoc} This implementation iterates over the list of child
     * declarations and asks them for the bean class name. The first
     * non-<b>null</b> value is returned. If none of the child declarations have
     * a defined bean class, result is <b>null</b>.
     */
    @Override
    public String getBeanClassName()
    {
        for (BeanDeclaration d : childDeclarations)
        {
            String beanClassName = d.getBeanClassName();
            if (beanClassName != null)
            {
                return beanClassName;
            }
        }
        return null;
    }

    /**
     * {@inheritDoc} This implementation creates a union of the properties
     * returned by all child declarations. If a property is defined in multiple
     * child declarations, the declaration that comes before in the list of
     * children takes precedence.
     */
    @Override
    public Map<String, Object> getBeanProperties()
    {
        Map<String, Object> result = new HashMap<String, Object>();
        for (int i = childDeclarations.size() - 1; i >= 0; i--)
        {
            Map<String, Object> props =
                    childDeclarations.get(i).getBeanProperties();
            if (props != null)
            {
                result.putAll(props);
            }
        }
        return result;
    }

    /**
     * {@inheritDoc} This implementation creates a union of the nested bean
     * declarations returned by all child declarations. If a complex property is
     * defined in multiple child declarations, the declaration that comes before
     * in the list of children takes precedence.
     */
    @Override
    public Map<String, Object> getNestedBeanDeclarations()
    {
        Map<String, Object> result = new HashMap<String, Object>();
        for (int i = childDeclarations.size() - 1; i >= 0; i--)
        {
            Map<String, Object> decls =
                    childDeclarations.get(i).getNestedBeanDeclarations();
            if (decls != null)
            {
                result.putAll(decls);
            }
        }
        return result;
    }

    /**
     * {@inheritDoc} This implementation iterates over the list of child
     * declarations and asks them for constructor arguments. The first
     * non-<b>null</b> and non empty collection is returned. If none of the
     * child declarations provide constructor arguments, result is an empty
     * collection.
     */
    @Override
    public Collection<ConstructorArg> getConstructorArgs()
    {
        for (BeanDeclaration d : childDeclarations)
        {
            Collection<ConstructorArg> args = d.getConstructorArgs();
            if (args != null && !args.isEmpty())
            {
                return args;
            }
        }
        return Collections.emptyList();
    }
}