    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 *     https://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.interpol;
    018
    019import java.util.ArrayList;
    020import java.util.Collection;
    021import java.util.Collections;
    022import java.util.HashMap;
    023import java.util.LinkedList;
    024import java.util.Map;
    025import java.util.function.Function;
    026
    027/**
    028 * <p>
    029 * A simple value class defining a {@link ConfigurationInterpolator}.
    030 * </p>
    031 * <p>
    032 * Objects of this class can be used for creating new {@code ConfigurationInterpolator} instances; they contain all
    033 * required properties. It is either possible to set a fully initialized {@code ConfigurationInterpolator} directly
    034 * which can be used as is. Alternatively, some or all properties of an instance to be newly created can be set. These
    035 * properties include
    036 * </p>
    037 * <ul>
    038 * <li>a map with {@code Lookup} objects associated with a specific prefix</li>
    039 * <li>a collection with default {@code Lookup} objects (without a prefix)</li>
    040 * <li>a parent {@code ConfigurationInterpolator}</li>
    041 * <li>a function used to convert interpolated values into strings</li>
    042 * </ul>
    043 * <p>
    044 * When setting up a configuration it is possible to define the {@code ConfigurationInterpolator} in terms of this
    045 * class. The configuration will then either use the {@code ConfigurationInterpolator} instance explicitly defined in
    046 * the {@code InterpolatorSpecification} instance or create a new one.
    047 * </p>
    048 * <p>
    049 * Instances are not created directly, but using the nested {@code Builder} class. They are then immutable.
    050 * </p>
    051 *
    052 * @since 2.0
    053 */
    054public final class InterpolatorSpecification {
    055
    056    /**
    057     * <p>
    058     * A <em>builder</em> class for creating instances of {@code InterpolatorSpecification}.
    059     * </p>
    060     * <p>
    061     * This class provides a fluent API for defining the various properties of an {@code InterpolatorSpecification} object.
    062     * <em>Note:</em> This builder class is not thread-safe.
    063     * </p>
    064     */
    065    public static class Builder {
    066
    067        /**
    068         * Helper method for checking a lookup. Throws an exception if the lookup is <strong>null</strong>.
    069         *
    070         * @param lookup the lookup to be checked
    071         * @throws IllegalArgumentException if the lookup is <strong>null</strong>
    072         */
    073        private static void checkLookup(final Lookup lookup) {
    074            if (lookup == null) {
    075                throw new IllegalArgumentException("Lookup must not be null.");
    076            }
    077        }
    078
    079        /** A map with prefix lookups. */
    080        private final Map<String, Lookup> prefixLookups;
    081
    082        /** A collection with default lookups. */
    083        private final Collection<Lookup> defLookups;
    084
    085        /** The {@code ConfigurationInterpolator}. */
    086        private ConfigurationInterpolator interpolator;
    087
    088        /** The parent {@code ConfigurationInterpolator}. */
    089        private ConfigurationInterpolator parentInterpolator;
    090
    091        /** Function used to convert interpolated values to strings. */
    092        private Function<Object, String> stringConverter;
    093
    094        /**
    095         * Constructs a new instance.
    096         */
    097        public Builder() {
    098            prefixLookups = new HashMap<>();
    099            defLookups = new LinkedList<>();
    100        }
    101
    102        /**
    103         * Creates a new {@code InterpolatorSpecification} instance with the properties set so far. After that this builder
    104         * instance is reset so that it can be reused for creating further specification objects.
    105         *
    106         * @return the newly created {@code InterpolatorSpecification}
    107         */
    108        public InterpolatorSpecification create() {
    109            final InterpolatorSpecification spec = new InterpolatorSpecification(this);
    110            reset();
    111            return spec;
    112        }
    113
    114        /**
    115         * Removes all data from this builder. Afterwards it can be used to define a brand new {@code InterpolatorSpecification}
    116         * object.
    117         */
    118        public void reset() {
    119            interpolator = null;
    120            parentInterpolator = null;
    121            prefixLookups.clear();
    122            defLookups.clear();
    123            stringConverter = null;
    124        }
    125
    126        /**
    127         * Adds the given {@code Lookup} object to the list of default lookups.
    128         *
    129         * @param lookup the {@code Lookup} (must not be <strong>null</strong>)
    130         * @return a reference to this builder for method chaining
    131         * @throws IllegalArgumentException if the {@code Lookup} is <strong>null</strong>
    132         */
    133        public Builder withDefaultLookup(final Lookup lookup) {
    134            checkLookup(lookup);
    135            defLookups.add(lookup);
    136            return this;
    137        }
    138
    139        /**
    140         * Adds the content of the given collection to the default lookups managed by this builder. The collection can be
    141         * <strong>null</strong>, then this method has no effect.
    142         *
    143         * @param lookups the collection with lookups to be added
    144         * @return a reference to this builder for method chaining
    145         * @throws IllegalArgumentException if the collection contains <strong>null</strong> entries
    146         */
    147        public Builder withDefaultLookups(final Collection<? extends Lookup> lookups) {
    148            if (lookups != null) {
    149                lookups.forEach(this::withDefaultLookup);
    150            }
    151            return this;
    152        }
    153
    154        /**
    155         * Sets the {@code ConfigurationInterpolator} instance for the {@code InterpolatorSpecification}. This means that a
    156         * {@code ConfigurationInterpolator} has been created and set up externally and can be used directly.
    157         *
    158         * @param ci the {@code ConfigurationInterpolator} (can be <strong>null</strong>)
    159         * @return a reference to this builder for method chaining
    160         */
    161        public Builder withInterpolator(final ConfigurationInterpolator ci) {
    162            interpolator = ci;
    163            return this;
    164        }
    165
    166        /**
    167         * Sets an optional parent {@code ConfigurationInterpolator}. If defined, this object is set as parent of a newly
    168         * created {@code ConfigurationInterpolator} instance.
    169         *
    170         * @param parent the parent {@code ConfigurationInterpolator} (can be <strong>null</strong>)
    171         * @return a reference to this builder for method chaining
    172         */
    173        public Builder withParentInterpolator(final ConfigurationInterpolator parent) {
    174            parentInterpolator = parent;
    175            return this;
    176        }
    177
    178        /**
    179         * Adds a {@code Lookup} object for a given prefix.
    180         *
    181         * @param prefix the prefix (must not be <strong>null</strong>)
    182         * @param lookup the {@code Lookup} (must not be <strong>null</strong>)
    183         * @return a reference to this builder for method chaining
    184         * @throws IllegalArgumentException if a required parameter is missing
    185         */
    186        public Builder withPrefixLookup(final String prefix, final Lookup lookup) {
    187            if (prefix == null) {
    188                throw new IllegalArgumentException("Prefix must not be null.");
    189            }
    190            checkLookup(lookup);
    191            prefixLookups.put(prefix, lookup);
    192            return this;
    193        }
    194
    195        /**
    196         * Adds the content of the given map to the prefix lookups managed by this builder. The map can be <strong>null</strong>, then
    197         * this method has no effect.
    198         *
    199         * @param lookups the map with prefix lookups to be added
    200         * @return a reference to this builder for method chaining
    201         * @throws IllegalArgumentException if the map contains <strong>null</strong> values
    202         */
    203        public Builder withPrefixLookups(final Map<String, ? extends Lookup> lookups) {
    204            if (lookups != null) {
    205                lookups.forEach(this::withPrefixLookup);
    206            }
    207            return this;
    208        }
    209
    210        /**
    211         * Sets the function used to convert interpolated values to strings. Pass {@code null}
    212         * if the default conversion function is to be used.
    213         *
    214         * @param fn function used to convert interpolated values to string or {@code null} if the
    215         *      default conversion function is to be used
    216         * @return a reference to this builder for method chaining
    217         */
    218        public Builder withStringConverter(final Function<Object, String> fn) {
    219            this.stringConverter = fn;
    220            return this;
    221        }
    222    }
    223
    224    /** The {@code ConfigurationInterpolator} instance to be used directly. */
    225    private final ConfigurationInterpolator interpolator;
    226
    227    /** The parent {@code ConfigurationInterpolator}. */
    228    private final ConfigurationInterpolator parentInterpolator;
    229
    230    /** The map with prefix lookups. */
    231    private final Map<String, Lookup> prefixLookups;
    232
    233    /** The collection with default lookups. */
    234    private final Collection<Lookup> defaultLookups;
    235
    236    /** Function used to convert interpolated values to strings. */
    237    private final Function<Object, String> stringConverter;
    238
    239    /**
    240     * Creates a new instance of {@code InterpolatorSpecification} with the properties defined by the given builder object.
    241     *
    242     * @param builder the builder
    243     */
    244    private InterpolatorSpecification(final Builder builder) {
    245        interpolator = builder.interpolator;
    246        parentInterpolator = builder.parentInterpolator;
    247        prefixLookups = Collections.unmodifiableMap(new HashMap<>(builder.prefixLookups));
    248        defaultLookups = Collections.unmodifiableCollection(new ArrayList<>(builder.defLookups));
    249        stringConverter = builder.stringConverter;
    250    }
    251
    252    /**
    253     * Gets a collection with the default lookups.
    254     *
    255     * @return the default lookups for a new {@code ConfigurationInterpolator} instance (never <strong>null</strong>)
    256     */
    257    public Collection<Lookup> getDefaultLookups() {
    258        return defaultLookups;
    259    }
    260
    261    /**
    262     * Gets the {@code ConfigurationInterpolator} instance to be used directly.
    263     *
    264     * @return the {@code ConfigurationInterpolator} (can be <strong>null</strong>)
    265     */
    266    public ConfigurationInterpolator getInterpolator() {
    267        return interpolator;
    268    }
    269
    270    /**
    271     * Gets the parent {@code ConfigurationInterpolator} object.
    272     *
    273     * @return the parent {@code ConfigurationInterpolator} (can be <strong>null</strong>)
    274     */
    275    public ConfigurationInterpolator getParentInterpolator() {
    276        return parentInterpolator;
    277    }
    278
    279    /**
    280     * Gets a map with prefix lookups. The keys of the map are the prefix strings, its values are the corresponding
    281     * {@code Lookup} objects.
    282     *
    283     * @return the prefix lookups for a new {@code ConfigurationInterpolator} instance (never <strong>null</strong>)
    284     */
    285    public Map<String, Lookup> getPrefixLookups() {
    286        return prefixLookups;
    287    }
    288
    289    /**
    290     * Gets the function used to convert interpolated values to strings or {@code null}
    291     * if the default conversion function is to be used.
    292     *
    293     * @return function used to convert interpolated values to strings or {@code null} if
    294     *      the default conversion function is to be used
    295     */
    296    public Function<Object, String> getStringConverter() {
    297        return stringConverter;
    298    }
    299}