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.lang3.text;
018
019import java.util.Map;
020
021import org.apache.commons.lang3.SystemProperties;
022
023/**
024 * Lookup a String key to a String value.
025 * <p>
026 * This class represents the simplest form of a string to string map.
027 * It has a benefit over a map in that it can create the result on
028 * demand based on the key.
029 * </p>
030 * <p>
031 * This class comes complete with various factory methods.
032 * If these do not suffice, you can subclass and implement your own matcher.
033 * </p>
034 * <p>
035 * For example, it would be possible to implement a lookup that used the
036 * key as a primary key, and looked up the value on demand from the database.
037 * </p>
038 *
039 * @param <V> Unused.
040 * @since 2.2
041 * @deprecated As of 3.6, use Apache Commons Text
042 * <a href="https://commons.apache.org/proper/commons-text/javadocs/api-release/org/apache/commons/text/lookup/StringLookupFactory.html">
043 * StringLookupFactory</a> instead
044 */
045@Deprecated
046public abstract class StrLookup<V> {
047
048    /**
049     * Lookup that always returns null.
050     */
051    private static final StrLookup<String> NONE_LOOKUP = new MapStrLookup<>(null);
052
053    /**
054     * Lookup based on system properties.
055     */
056    private static final StrLookup<String> SYSTEM_PROPERTIES_LOOKUP = new SystemPropertiesStrLookup();
057
058    /**
059     * Returns a lookup which always returns null.
060     *
061     * @return a lookup that always returns null, not null
062     */
063    public static StrLookup<?> noneLookup() {
064        return NONE_LOOKUP;
065    }
066
067    /**
068     * Returns a new lookup which uses a copy of the current
069     * {@link System#getProperties() System properties}.
070     * <p>
071     * If a security manager blocked access to system properties, then null will
072     * be returned from every lookup.
073     * </p>
074     * <p>
075     * If a null key is used, this lookup will throw a NullPointerException.
076     * </p>
077     *
078     * @return a lookup using system properties, not null
079     */
080    public static StrLookup<String> systemPropertiesLookup() {
081        return SYSTEM_PROPERTIES_LOOKUP;
082    }
083
084    /**
085     * Returns a lookup which looks up values using a map.
086     * <p>
087     * If the map is null, then null will be returned from every lookup.
088     * The map result object is converted to a string using toString().
089     * </p>
090     *
091     * @param <V> the type of the values supported by the lookup
092     * @param map  the map of keys to values, may be null
093     * @return a lookup using the map, not null
094     */
095    public static <V> StrLookup<V> mapLookup(final Map<String, V> map) {
096        return new MapStrLookup<>(map);
097    }
098
099    /**
100     * Constructor.
101     */
102    protected StrLookup() {
103    }
104
105    /**
106     * Looks up a String key to a String value.
107     * <p>
108     * The internal implementation may use any mechanism to return the value.
109     * The simplest implementation is to use a Map. However, virtually any
110     * implementation is possible.
111     * </p>
112     * <p>
113     * For example, it would be possible to implement a lookup that used the
114     * key as a primary key, and looked up the value on demand from the database
115     * Or, a numeric based implementation could be created that treats the key
116     * as an integer, increments the value and return the result as a string -
117     * converting 1 to 2, 15 to 16 etc.
118     * </p>
119     * <p>
120     * The {@link #lookup(String)} method always returns a String, regardless of
121     * the underlying data, by converting it as necessary. For example:
122     * </p>
123     * <pre>
124     * Map&lt;String, Object&gt; map = new HashMap&lt;String, Object&gt;();
125     * map.put("number", Integer.valueOf(2));
126     * assertEquals("2", StrLookup.mapLookup(map).lookup("number"));
127     * </pre>
128     * @param key  the key to be looked up, may be null
129     * @return the matching value, null if no match
130     */
131    public abstract String lookup(String key);
132
133    /**
134     * Lookup implementation that uses a Map.
135     *
136     * @param <V> the type of mapped values.
137     */
138    static class MapStrLookup<V> extends StrLookup<V> {
139
140        /** Map keys are variable names and value. */
141        private final Map<String, V> map;
142
143        /**
144         * Creates a new instance backed by a Map.
145         *
146         * @param map  the map of keys to values, may be null
147         */
148        MapStrLookup(final Map<String, V> map) {
149            this.map = map;
150        }
151
152        /**
153         * Looks up a String key to a String value using the map.
154         * <p>
155         * If the map is null, then null is returned.
156         * The map result object is converted to a string using toString().
157         * </p>
158         *
159         * @param key  the key to be looked up, may be null
160         * @return the matching value, null if no match
161         */
162        @Override
163        public String lookup(final String key) {
164            if (map == null) {
165                return null;
166            }
167            final Object obj = map.get(key);
168            if (obj == null) {
169                return null;
170            }
171            return obj.toString();
172        }
173    }
174
175    /**
176     * Lookup implementation based on system properties.
177     */
178    private static class SystemPropertiesStrLookup extends StrLookup<String> {
179        /**
180         * {@inheritDoc} This implementation directly accesses system properties.
181         */
182        @Override
183        public String lookup(final String key) {
184            return SystemProperties.getProperty(key);
185        }
186    }
187}