    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 */
    017package org.apache.commons.configuration2.builder.combined;
    018
    019import java.util.HashMap;
    020import java.util.Map;
    021import java.util.concurrent.ConcurrentHashMap;
    022import java.util.concurrent.ConcurrentMap;
    023import java.util.concurrent.atomic.AtomicReference;
    024
    025import org.apache.commons.configuration2.ConfigurationUtils;
    026import org.apache.commons.configuration2.FileBasedConfiguration;
    027import org.apache.commons.configuration2.builder.BasicBuilderParameters;
    028import org.apache.commons.configuration2.builder.BasicConfigurationBuilder;
    029import org.apache.commons.configuration2.builder.BuilderParameters;
    030import org.apache.commons.configuration2.builder.ConfigurationBuilderEvent;
    031import org.apache.commons.configuration2.builder.ConfigurationBuilderResultCreatedEvent;
    032import org.apache.commons.configuration2.builder.FileBasedConfigurationBuilder;
    033import org.apache.commons.configuration2.event.Event;
    034import org.apache.commons.configuration2.event.EventListener;
    035import org.apache.commons.configuration2.event.EventListenerList;
    036import org.apache.commons.configuration2.event.EventType;
    037import org.apache.commons.configuration2.ex.ConfigurationException;
    038import org.apache.commons.configuration2.interpol.ConfigurationInterpolator;
    039import org.apache.commons.configuration2.interpol.InterpolatorSpecification;
    040import org.apache.commons.lang3.concurrent.ConcurrentUtils;
    041
    042/**
    043 * <p>
    044 * A specialized {@code ConfigurationBuilder} implementation providing access to multiple file-based configurations
    045 * based on a file name pattern.
    046 * </p>
    047 * <p>
    048 * This builder class is initialized with a pattern string and a {@link ConfigurationInterpolator} object. Each time a
    049 * configuration is requested, the pattern is evaluated against the {@code ConfigurationInterpolator} (so all variables
    050 * are replaced by their current values). The resulting string is interpreted as a file name for a configuration file to
    051 * be loaded. For example, providing a pattern of <em>file:///opt/config/${product}/${client}/config.xml</em> will
    052 * result in <em>product</em> and <em>client</em> being resolved on every call. By storing configuration files in a
    053 * corresponding directory structure, specialized configuration files associated with a specific product and client can
    054 * be loaded. Thus an application can be made multi-tenant in a transparent way.
    055 * </p>
    056 * <p>
    057 * This builder class keeps a map with configuration builders for configurations already loaded. The
    058 * {@code getConfiguration()} method first evaluates the pattern string and checks whether a builder for the resulting
    059 * file name is available. If yes, it is queried for its configuration. Otherwise, a new file-based configuration
    060 * builder is created now and initialized.
    061 * </p>
    062 * <p>
    063 * Configuration of an instance happens in the usual way for configuration builders. A
    064 * {@link MultiFileBuilderParametersImpl} parameters object is expected which must contain a file name pattern string
    065 * and a {@code ConfigurationInterpolator}. Other properties of this parameters object are used to initialize the
    066 * builders for managed configurations.
    067 * </p>
    068 *
    069 * @since 2.0
    070 * @param <T> the concrete type of {@code Configuration} objects created by this builder
    071 */
    072public class MultiFileConfigurationBuilder<T extends FileBasedConfiguration> extends BasicConfigurationBuilder<T> {
    073    /**
    074     * Constant for the name of the key referencing the {@code ConfigurationInterpolator} in this builder's parameters.
    075     */
    076    private static final String KEY_INTERPOLATOR = "interpolator";
    077
    078    /**
    079     * Creates a map with parameters for a new managed configuration builder. This method merges the basic parameters set
    080     * for this builder with the specific parameters object for managed builders (if provided).
    081     *
    082     * @param params the parameters of this builder
    083     * @param multiParams the parameters object for this builder
    084     * @return the parameters for a new managed builder
    085     */
    086    private static Map<String, Object> createManagedBuilderParameters(final Map<String, Object> params, final MultiFileBuilderParametersImpl multiParams) {
    087        final Map<String, Object> newParams = new HashMap<>(params);
    088        newParams.remove(KEY_INTERPOLATOR);
    089        final BuilderParameters managedBuilderParameters = multiParams.getManagedBuilderParameters();
    090        if (managedBuilderParameters != null) {
    091            // clone parameters as they are applied to multiple builders
    092            final BuilderParameters copy = (BuilderParameters) ConfigurationUtils.cloneIfPossible(managedBuilderParameters);
    093            newParams.putAll(copy.getParameters());
    094        }
    095        return newParams;
    096    }
    097
    098    /**
    099     * Checks whether the given event type is of interest for the managed configuration builders. This method is called by
    100     * the methods for managing event listeners to find out whether a listener should be passed to the managed builders,
    101     * too.
    102     *
    103     * @param eventType the event type object
    104     * @return a flag whether this event type is of interest for managed builders
    105     */
    106    private static boolean isEventTypeForManagedBuilders(final EventType<?> eventType) {
    107        return !EventType.isInstanceOf(eventType, ConfigurationBuilderEvent.ANY);
    108    }
    109
    110    /** A cache for already created managed builders. */
    111    private final ConcurrentMap<String, FileBasedConfigurationBuilder<T>> managedBuilders = new ConcurrentHashMap<>();
    112
    113    /** Stores the {@code ConfigurationInterpolator} object. */
    114    private final AtomicReference<ConfigurationInterpolator> interpolator = new AtomicReference<>();
    115
    116    /**
    117     * A flag for preventing reentrant access to managed builders on interpolation of the file name pattern.
    118     */
    119    private final ThreadLocal<Boolean> inInterpolation = new ThreadLocal<>();
    120
    121    /** A list for the event listeners to be passed to managed builders. */
    122    private final EventListenerList configurationListeners = new EventListenerList();
    123
    124    /**
    125     * A specialized event listener which gets registered at all managed builders. This listener just propagates
    126     * notifications from managed builders to the listeners registered at this {@code MultiFileConfigurationBuilder}.
    127     */
    128    private final EventListener<ConfigurationBuilderEvent> managedBuilderDelegationListener = this::handleManagedBuilderEvent;
    129
    130    /**
    131     * Creates a new instance of {@code MultiFileConfigurationBuilder} without setting initialization parameters.
    132     *
    133     * @param resCls the result configuration class
    134     * @throws IllegalArgumentException if the result class is <b>null</b>
    135     */
    136    public MultiFileConfigurationBuilder(final Class<? extends T> resCls) {
    137        super(resCls);
    138    }
    139
    140    /**
    141     * Creates a new instance of {@code MultiFileConfigurationBuilder} and sets initialization parameters.
    142     *
    143     * @param resCls the result configuration class
    144     * @param params a map with initialization parameters
    145     * @throws IllegalArgumentException if the result class is <b>null</b>
    146     */
    147    public MultiFileConfigurationBuilder(final Class<? extends T> resCls, final Map<String, Object> params) {
    148        super(resCls, params);
    149    }
    150
    151    /**
    152     * Creates a new instance of {@code MultiFileConfigurationBuilder} and sets initialization parameters and a flag whether
    153     * initialization failures should be ignored.
    154     *
    155     * @param resCls the result configuration class
    156     * @param params a map with initialization parameters
    157     * @param allowFailOnInit a flag whether initialization errors should be ignored
    158     * @throws IllegalArgumentException if the result class is <b>null</b>
    159     */
    160    public MultiFileConfigurationBuilder(final Class<? extends T> resCls, final Map<String, Object> params, final boolean allowFailOnInit) {
    161        super(resCls, params, allowFailOnInit);
    162    }
    163
    164    /**
    165     * {@inheritDoc} This implementation ensures that the listener is also added to managed configuration builders if
    166     * necessary. Listeners for the builder-related event types are excluded because otherwise they would be triggered by
    167     * the internally used configuration builders.
    168     */
    169    @Override
    170    public synchronized <E extends Event> void addEventListener(final EventType<E> eventType, final EventListener<? super E> l) {
    171        super.addEventListener(eventType, l);
    172        if (isEventTypeForManagedBuilders(eventType)) {
    173            getManagedBuilders().values().forEach(b -> b.addEventListener(eventType, l));
    174            configurationListeners.addEventListener(eventType, l);
    175        }
    176    }
    177
    178    /**
    179     * {@inheritDoc} This method is overridden to adapt the return type.
    180     */
    181    @Override
    182    public MultiFileConfigurationBuilder<T> configure(final BuilderParameters... params) {
    183        super.configure(params);
    184        return this;
    185    }
    186
    187    /**
    188     * Determines the file name of a configuration based on the file name pattern. This method is called on every access to
    189     * this builder's configuration. It obtains the {@link ConfigurationInterpolator} from this builder's parameters and
    190     * uses it to interpolate the file name pattern.
    191     *
    192     * @param multiParams the parameters object for this builder
    193     * @return the name of the configuration file to be loaded
    194     */
    195    protected String constructFileName(final MultiFileBuilderParametersImpl multiParams) {
    196        final ConfigurationInterpolator ci = getInterpolator();
    197        return String.valueOf(ci.interpolate(multiParams.getFilePattern()));
    198    }
    199
    200    /**
    201     * Creates a new {@code ConfigurationBuilderEvent} based on the passed in event, but with the source changed to this
    202     * builder. This method is called when an event was received from a managed builder. In this case, the event has to be
    203     * passed to the builder listeners registered at this object, but with the correct source property.
    204     *
    205     * @param event the event received from a managed builder
    206     * @return the event to be propagated
    207     */
    208    private ConfigurationBuilderEvent createEventWithChangedSource(final ConfigurationBuilderEvent event) {
    209        if (ConfigurationBuilderResultCreatedEvent.RESULT_CREATED.equals(event.getEventType())) {
    210            return new ConfigurationBuilderResultCreatedEvent(this, ConfigurationBuilderResultCreatedEvent.RESULT_CREATED,
    211                ((ConfigurationBuilderResultCreatedEvent) event).getConfiguration());
    212        }
    213        @SuppressWarnings("unchecked")
    214        final
    215        // This is safe due to the constructor of ConfigurationBuilderEvent
    216        EventType<? extends ConfigurationBuilderEvent> type = (EventType<? extends ConfigurationBuilderEvent>) event.getEventType();
    217        return new ConfigurationBuilderEvent(this, type);
    218    }
    219
    220    /**
    221     * Creates a fully initialized builder for a managed configuration. This method is called by {@code getConfiguration()}
    222     * whenever a configuration file is requested which has not yet been loaded. This implementation delegates to
    223     * {@code createManagedBuilder()} for actually creating the builder object. Then it sets the location to the
    224     * configuration file.
    225     *
    226     * @param fileName the name of the file to be loaded
    227     * @param params a map with initialization parameters for the new builder
    228     * @return the newly created and initialized builder instance
    229     * @throws ConfigurationException if an error occurs
    230     */
    231    protected FileBasedConfigurationBuilder<T> createInitializedManagedBuilder(final String fileName, final Map<String, Object> params)
    232        throws ConfigurationException {
    233        final FileBasedConfigurationBuilder<T> managedBuilder = createManagedBuilder(fileName, params);
    234        managedBuilder.getFileHandler().setFileName(fileName);
    235        return managedBuilder;
    236    }
    237
    238    /**
    239     * Creates the {@code ConfigurationInterpolator} to be used by this instance. This method is called when a file name is
    240     * to be constructed, but no current {@code ConfigurationInterpolator} instance is available. It obtains an instance
    241     * from this builder's parameters. If no properties of the {@code ConfigurationInterpolator} are specified in the
    242     * parameters, a default instance without lookups is returned (which is probably not very helpful).
    243     *
    244     * @return the {@code ConfigurationInterpolator} to be used
    245     */
    246    protected ConfigurationInterpolator createInterpolator() {
    247        final InterpolatorSpecification spec = BasicBuilderParameters.fetchInterpolatorSpecification(getParameters());
    248        return ConfigurationInterpolator.fromSpecification(spec);
    249    }
    250
    251    /**
    252     * Creates a builder for a managed configuration. This method is called whenever a configuration for a file name is
    253     * requested which has not yet been loaded. The passed in map with parameters is populated from this builder's
    254     * configuration (i.e. the basic parameters plus the optional parameters for managed builders). This base implementation
    255     * creates a standard builder for file-based configurations. Derived classes may override it to create special purpose
    256     * builders.
    257     *
    258     * @param fileName the name of the file to be loaded
    259     * @param params a map with initialization parameters for the new builder
    260     * @return the newly created builder instance
    261     * @throws ConfigurationException if an error occurs
    262     */
    263    protected FileBasedConfigurationBuilder<T> createManagedBuilder(final String fileName, final Map<String, Object> params) throws ConfigurationException {
    264        return new FileBasedConfigurationBuilder<>(getResultClass(), params, isAllowFailOnInit());
    265    }
    266
    267    /**
    268     * Generates a file name for a managed builder based on the file name pattern. This method prevents infinite loops which
    269     * could happen if the file name pattern cannot be resolved and the {@code ConfigurationInterpolator} used by this
    270     * object causes a recursive lookup to this builder's configuration.
    271     *
    272     * @param multiParams the current builder parameters
    273     * @return the file name for a managed builder
    274     */
    275    private String fetchFileName(final MultiFileBuilderParametersImpl multiParams) {
    276        String fileName;
    277        final Boolean reentrant = inInterpolation.get();
    278        if (reentrant != null && reentrant.booleanValue()) {
    279            fileName = multiParams.getFilePattern();
    280        } else {
    281            inInterpolation.set(Boolean.TRUE);
    282            try {
    283                fileName = constructFileName(multiParams);
    284            } finally {
    285                inInterpolation.set(Boolean.FALSE);
    286            }
    287        }
    288        return fileName;
    289    }
    290
    291    /**
    292     * {@inheritDoc} This implementation evaluates the file name pattern using the configured
    293     * {@code ConfigurationInterpolator}. If this file has already been loaded, the corresponding builder is accessed.
    294     * Otherwise, a new builder is created for loading this configuration file.
    295     */
    296    @Override
    297    public T getConfiguration() throws ConfigurationException {
    298        return getManagedBuilder().getConfiguration();
    299    }
    300
    301    /**
    302     * Gets the {@code ConfigurationInterpolator} used by this instance. This is the object used for evaluating the file
    303     * name pattern. It is created on demand.
    304     *
    305     * @return the {@code ConfigurationInterpolator}
    306     */
    307    protected ConfigurationInterpolator getInterpolator() {
    308        ConfigurationInterpolator result;
    309        boolean done;
    310
    311        // This might create multiple instances under high load,
    312        // however, always the same instance is returned.
    313        do {
    314            result = interpolator.get();
    315            if (result != null) {
    316                done = true;
    317            } else {
    318                result = createInterpolator();
    319                done = interpolator.compareAndSet(null, result);
    320            }
    321        } while (!done);
    322
    323        return result;
    324    }
    325
    326    /**
    327     * Gets the managed {@code FileBasedConfigurationBuilder} for the current file name pattern. It is determined based
    328     * on the evaluation of the file name pattern using the configured {@code ConfigurationInterpolator}. If this is the
    329     * first access to this configuration file, the builder is created.
    330     *
    331     * @return the configuration builder for the configuration corresponding to the current evaluation of the file name
    332     *         pattern
    333     * @throws ConfigurationException if the builder cannot be determined (e.g. due to missing initialization parameters)
    334     */
    335    public FileBasedConfigurationBuilder<T> getManagedBuilder() throws ConfigurationException {
    336        final Map<String, Object> params = getParameters();
    337        final MultiFileBuilderParametersImpl multiParams = MultiFileBuilderParametersImpl.fromParameters(params, true);
    338        if (multiParams.getFilePattern() == null) {
    339            throw new ConfigurationException("No file name pattern is set!");
    340        }
    341        final String fileName = fetchFileName(multiParams);
    342
    343        FileBasedConfigurationBuilder<T> builder = getManagedBuilders().get(fileName);
    344        if (builder == null) {
    345            builder = createInitializedManagedBuilder(fileName, createManagedBuilderParameters(params, multiParams));
    346            final FileBasedConfigurationBuilder<T> newBuilder = ConcurrentUtils.putIfAbsent(getManagedBuilders(), fileName, builder);
    347            if (newBuilder == builder) {
    348                initListeners(newBuilder);
    349            } else {
    350                builder = newBuilder;
    351            }
    352        }
    353        return builder;
    354    }
    355
    356    /**
    357     * Gets the map with the managed builders created so far by this {@code MultiFileConfigurationBuilder}. This map is
    358     * exposed to derived classes so they can access managed builders directly. However, derived classes are not expected to
    359     * manipulate this map.
    360     *
    361     * @return the map with the managed builders
    362     */
    363    protected ConcurrentMap<String, FileBasedConfigurationBuilder<T>> getManagedBuilders() {
    364        return managedBuilders;
    365    }
    366
    367    /**
    368     * Handles events received from managed configuration builders. This method creates a new event with a source pointing
    369     * to this builder and propagates it to all registered listeners.
    370     *
    371     * @param event the event received from a managed builder
    372     */
    373    private void handleManagedBuilderEvent(final ConfigurationBuilderEvent event) {
    374        if (ConfigurationBuilderEvent.RESET.equals(event.getEventType())) {
    375            resetResult();
    376        } else {
    377            fireBuilderEvent(createEventWithChangedSource(event));
    378        }
    379    }
    380
    381    /**
    382     * Registers event listeners at the passed in newly created managed builder. This method registers a special
    383     * {@code EventListener} which propagates builder events to listeners registered at this builder. In addition,
    384     * {@code ConfigurationListener} and {@code ConfigurationErrorListener} objects are registered at the new builder.
    385     *
    386     * @param newBuilder the builder to be initialized
    387     */
    388    private void initListeners(final FileBasedConfigurationBuilder<T> newBuilder) {
    389        copyEventListeners(newBuilder, configurationListeners);
    390        newBuilder.addEventListener(ConfigurationBuilderEvent.ANY, managedBuilderDelegationListener);
    391    }
    392
    393    /**
    394     * {@inheritDoc} This implementation ensures that the listener is also removed from managed configuration builders if
    395     * necessary.
    396     */
    397    @Override
    398    public synchronized <E extends Event> boolean removeEventListener(final EventType<E> eventType, final EventListener<? super E> l) {
    399        final boolean result = super.removeEventListener(eventType, l);
    400        if (isEventTypeForManagedBuilders(eventType)) {
    401            getManagedBuilders().values().forEach(b -> b.removeEventListener(eventType, l));
    402            configurationListeners.removeEventListener(eventType, l);
    403        }
    404        return result;
    405    }
    406
    407    /**
    408     * {@inheritDoc} This implementation clears the cache with all managed builders.
    409     */
    410    @Override
    411    public synchronized void resetParameters() {
    412        getManagedBuilders().values().forEach(b -> b.removeEventListener(ConfigurationBuilderEvent.ANY, managedBuilderDelegationListener));
    413        getManagedBuilders().clear();
    414        interpolator.set(null);
    415        super.resetParameters();
    416    }
    417}