CombinedConfigurationBuilderProvider.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.builder.combined;

import java.util.Arrays;
import java.util.Collection;

import org.apache.commons.configuration2.CombinedConfiguration;
import org.apache.commons.configuration2.Configuration;
import org.apache.commons.configuration2.builder.BasicBuilderParameters;
import org.apache.commons.configuration2.builder.BasicConfigurationBuilder;
import org.apache.commons.configuration2.builder.BuilderParameters;

/**
 * <p>
 * A specialized {@code ConfigurationBuilderProvider} implementation which deals with combined configuration builders.
 * </p>
 * <p>
 * This class is used to support {@code <configuration>} elements in configuration definition files. The provider
 * creates another {@link CombinedConfigurationBuilder} which inherits some of the properties from its parent builder.
 * </p>
 *
 * @since 2.0
 */
public class CombinedConfigurationBuilderProvider extends BaseConfigurationBuilderProvider {
    /** Constant for the name of the supported builder class. */
    private static final String BUILDER_CLASS = "org.apache.commons.configuration2.builder.combined.CombinedConfigurationBuilder";

    /** Constant for the name of the supported reloading builder class. */
    private static final String RELOADING_BUILDER_CLASS = "org.apache.commons.configuration2.builder.combined.ReloadingCombinedConfigurationBuilder";

    /** Constant for the name of the supported configuration class. */
    private static final String CONFIGURATION_CLASS = "org.apache.commons.configuration2.CombinedConfiguration";

    /** Constant for the combined configuration builder parameters class. */
    private static final String COMBINED_PARAMS = "org.apache.commons.configuration2.builder.combined.CombinedBuilderParametersImpl";

    /** Constant for the name of the file-based builder parameters class. */
    private static final String FILE_PARAMS = "org.apache.commons.configuration2.builder.FileBasedBuilderParametersImpl";

    /**
     * Populates the specified parameters object with properties from the given configuration. This method is used to set
     * default values for basic properties based on the result configuration of the parent builder.
     *
     * @param config the configuration whose properties are to be copied
     * @param params the target parameters object
     */
    private static void setUpBasicParameters(final CombinedConfiguration config, final BasicBuilderParameters params) {
        params.setListDelimiterHandler(config.getListDelimiterHandler()).setLogger(config.getLogger())
            .setThrowExceptionOnMissing(config.isThrowExceptionOnMissing()).setConfigurationDecoder(config.getConfigurationDecoder());
    }

    /**
     * Creates a new instance of {@code CombinedConfigurationBuilderProvider}.
     */
    public CombinedConfigurationBuilderProvider() {
        super(BUILDER_CLASS, RELOADING_BUILDER_CLASS, CONFIGURATION_CLASS, Arrays.asList(COMBINED_PARAMS, FILE_PARAMS));
    }

    /**
     * {@inheritDoc} This implementation creates the result builder object directly, not using reflection. (The
     * reflection-based approach of the base class does not work here because a combined configuration builder has
     * constructors with a different signature.) It also performs some additional initializations.
     */
    @Override
    protected BasicConfigurationBuilder<? extends Configuration> createBuilder(final ConfigurationDeclaration decl, final Collection<BuilderParameters> params)
        throws Exception {
        final CombinedConfigurationBuilder builder;
        if (decl.isReload()) {
            builder = new ReloadingCombinedConfigurationBuilder();
        } else {
            builder = new CombinedConfigurationBuilder();
        }
        decl.getConfigurationBuilder().initChildEventListeners(builder);
        return builder;
    }

    /**
     * {@inheritDoc} This implementation pre-fills basic parameters from the basic properties of the parent builder's result
     * configuration.
     */
    @Override
    protected void initializeParameterObjects(final ConfigurationDeclaration decl, final Collection<BuilderParameters> params) throws Exception {
        // we know that the first object is the combined builder parameters
        // object
        final BasicBuilderParameters basicParams = (BasicBuilderParameters) params.iterator().next();
        setUpBasicParameters(decl.getConfigurationBuilder().getConfigurationUnderConstruction(), basicParams);
        // now properties set explicitly can be overridden
        super.initializeParameterObjects(decl, params);
    }
}