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