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