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