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