MapConfiguration.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;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Properties;

import org.apache.commons.configuration2.ex.ConfigurationRuntimeException;

/**
 * <p>
 * A Map based Configuration.
 * </p>
 * <p>
 * This implementation of the {@code Configuration} interface is initialized with a {@link java.util.Map}. The methods
 * of the {@code Configuration} interface are implemented on top of the content of this map. The following storage
 * scheme is used:
 * </p>
 * <p>
 * Property keys are directly mapped to map keys, i.e. the {@code getProperty()} method directly performs a
 * {@code get()} on the map. Analogously, {@code setProperty()} or {@code addProperty()} operations write new data into
 * the map. If a value is added to an existing property, a {@link java.util.List} is created, which stores the values of
 * this property.
 * </p>
 * <p>
 * An important use case of this class is to treat a map as a {@code Configuration} allowing access to its data through
 * the richer interface. This can be a bit problematic in some cases because the map may contain values that need not
 * adhere to the default storage scheme used by typical configuration implementations, for example regarding lists. In such
 * cases care must be taken when manipulating the data through the {@code Configuration} interface, for example by calling
 * {@code addProperty()}; results may be different than expected.
 * </p>
 * <p>
 * The handling of list delimiters is a bit different for this configuration implementation: When a property of type
 * String is queried, it is passed to the current {@link org.apache.commons.configuration2.convert.ListDelimiterHandler
 * ListDelimiterHandler} which may generate multiple values. Note that per default a list delimiter handler is set which
 * does not do any list splitting, so this feature is disabled. It can be enabled by setting a properly configured
 * {@code ListDelimiterHandler} implementation, for example a
 * {@link org.apache.commons.configuration2.convert.DefaultListDelimiterHandler DefaultListDelimiterHandler} object.
 * </p>
 * <p>
 * Notice that list splitting is only performed for single string values. If a property has multiple values, the single
 * values are not split even if they contain the list delimiter character.
 * </p>
 * <p>
 * As the underlying {@code Map} is directly used as store of the property values, the thread-safety of this
 * {@code Configuration} implementation depends on the map passed to the constructor.
 * </p>
 * <p>
 * Notes about type safety: For properties with multiple values this implementation creates lists of type {@code Object}
 * and stores them. If a property is assigned another value, the value is added to the list. This can cause problems if
 * the map passed to the constructor already contains lists of other types. This should be avoided, otherwise it cannot
 * be guaranteed that the application might throw {@code ClassCastException} exceptions later.
 * </p>
 *
 * @since 1.1
 */
public class MapConfiguration extends AbstractConfiguration implements Cloneable {
    /**
     * Helper method for converting the type of the {@code Properties} object to a supported map type. As stated by the
     * comment of the constructor, we expect the {@code Properties} object to contain only String key; therefore, it is safe
     * to do this cast.
     *
     * @param props the {@code Properties} to be copied
     * @return a newly created map with all string keys of the properties
     */
    @SuppressWarnings("unchecked")
    private static Map<String, Object> toMap(final Properties props) {
        @SuppressWarnings("rawtypes")
        final Map map = props;
        return map;
    }

    /** The Map decorated by this configuration. */
    protected Map<String, Object> map;

    /** A flag whether trimming of property values should be disabled. */
    private boolean trimmingDisabled;

    /**
     * Create a Configuration decorator around the specified Map. The map is used to store the configuration properties, any
     * change will also affect the Map.
     *
     * @param map the map
     */
    public MapConfiguration(final Map<String, ?> map) {
        this.map = (Map<String, Object>) Objects.requireNonNull(map, "map");
    }

    /**
     * Creates a new instance of {@code MapConfiguration} which uses the specified {@code Properties} object as its data
     * store. All changes of this configuration affect the given {@code Properties} object and vice versa. Note that while
     * {@code Properties} actually implements {@code Map<Object, Object>}, we expect it to contain only string keys. Other
     * key types will lead to {@code ClassCastException} exceptions on certain methods.
     *
     * @param props the {@code Properties} object defining the content of this configuration
     * @since 1.8
     */
    public MapConfiguration(final Properties props) {
        map = toMap(Objects.requireNonNull(props));
    }

    @Override
    protected void addPropertyDirect(final String key, final Object value) {
        final Object previousValue = getProperty(key);

        if (previousValue == null) {
            map.put(key, value);
        } else if (previousValue instanceof List) {
            // the value is added to the existing list
            // Note: This is problematic. See header comment!
            ((List<Object>) previousValue).add(value);
        } else {
            // the previous value is replaced by a list containing the previous value and the new value
            final List<Object> list = new ArrayList<>();
            list.add(previousValue);
            list.add(value);

            map.put(key, list);
        }
    }

    @Override
    protected void clearPropertyDirect(final String key) {
        map.remove(key);
    }

    /**
     * Returns a copy of this object. The returned configuration will contain the same properties as the original. Event
     * listeners are not cloned.
     *
     * @return the copy
     * @since 1.3
     */
    @Override
    public Object clone() {
        try {
            final MapConfiguration copy = (MapConfiguration) super.clone();
            // Safe because ConfigurationUtils returns a map of the same types.
            @SuppressWarnings("unchecked")
            final Map<String, Object> clonedMap = (Map<String, Object>) ConfigurationUtils.clone(map);
            copy.map = clonedMap;
            copy.cloneInterpolator(this);
            return copy;
        } catch (final CloneNotSupportedException cex) {
            // cannot happen
            throw new ConfigurationRuntimeException(cex);
        }
    }

    @Override
    protected boolean containsKeyInternal(final String key) {
        return map.containsKey(key);
    }

    /**
     * Tests whether this configuration contains one or more matches to this value. This operation stops at first match
     * but may be more expensive than the containsKey method.
     * @since 2.11.0
     */
    @Override
    protected boolean containsValueInternal(final Object value) {
        return value != null && map.containsValue(value);
    }

    @Override
    protected Iterator<String> getKeysInternal() {
        return map.keySet().iterator();
    }

    /**
     * Gets the Map decorated by this configuration.
     *
     * @return the map this configuration is based onto
     */
    public Map<String, Object> getMap() {
        return map;
    }

    @Override
    protected Object getPropertyInternal(final String key) {
        final Object value = map.get(key);
        if (value instanceof String) {
            final Collection<String> list = getListDelimiterHandler().split((String) value, !isTrimmingDisabled());
            return list.size() > 1 ? list : list.iterator().next();
        }
        return value;
    }

    @Override
    protected boolean isEmptyInternal() {
        return map.isEmpty();
    }

    /**
     * Returns the flag whether trimming of property values is disabled.
     *
     * @return <strong>true</strong> if trimming of property values is disabled; <strong>false</strong> otherwise
     * @since 1.7
     */
    public boolean isTrimmingDisabled() {
        return trimmingDisabled;
    }

    /**
     * Sets a flag whether trimming of property values is disabled. This flag is only evaluated if list splitting is
     * enabled. Refer to the header comment for more information about list splitting and trimming.
     *
     * @param trimmingDisabled a flag whether trimming of property values should be disabled
     * @since 1.7
     */
    public void setTrimmingDisabled(final boolean trimmingDisabled) {
        this.trimmingDisabled = trimmingDisabled;
    }

    @Override
    protected int sizeInternal() {
        return map.size();
    }

    /**
     * Converts this object to a String suitable for debugging and logging.
     *
     * @since 2.3
     */
    @Override
    public String toString() {
        return getClass().getSimpleName() + " [map=" + map + ", trimmingDisabled=" + trimmingDisabled + "]";
    }
}