1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * https://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.lang3.text;
18
19 import java.util.Map;
20 import java.util.Objects;
21
22 import org.apache.commons.lang3.SystemProperties;
23
24 /**
25 * Lookup a String key to a String value.
26 * <p>
27 * This class represents the simplest form of a string to string map.
28 * It has a benefit over a map in that it can create the result on
29 * demand based on the key.
30 * </p>
31 * <p>
32 * This class comes complete with various factory methods.
33 * If these do not suffice, you can subclass and implement your own matcher.
34 * </p>
35 * <p>
36 * For example, it would be possible to implement a lookup that used the
37 * key as a primary key, and looked up the value on demand from the database.
38 * </p>
39 *
40 * @param <V> Unused.
41 * @since 2.2
42 * @deprecated As of <a href="https://commons.apache.org/proper/commons-lang/changes-report.html#a3.6">3.6</a>, use Apache Commons Text
43 * <a href="https://commons.apache.org/proper/commons-text/javadocs/api-release/org/apache/commons/text/lookup/StringLookupFactory.html">
44 * StringLookupFactory</a>.
45 */
46 @Deprecated
47 public abstract class StrLookup<V> {
48
49 /**
50 * Lookup implementation that uses a Map.
51 *
52 * @param <V> the type of mapped values.
53 */
54 private static final class MapStrLookup<V> extends StrLookup<V> {
55
56 /** Map keys are variable names and value. */
57 private final Map<String, V> map;
58
59 /**
60 * Creates a new instance backed by a Map.
61 *
62 * @param map the map of keys to values, may be null.
63 */
64 MapStrLookup(final Map<String, V> map) {
65 this.map = map;
66 }
67
68 /**
69 * Looks up a String key to a String value using the map.
70 * <p>
71 * If the map is null, then null is returned.
72 * The map result object is converted to a string using toString().
73 * </p>
74 *
75 * @param key the key to be looked up, may be null.
76 * @return the matching value, null if no match.
77 */
78 @Override
79 public String lookup(final String key) {
80 if (map == null) {
81 return null;
82 }
83 return Objects.toString(map.get(key), null);
84 }
85 }
86
87 /**
88 * Lookup implementation based on system properties.
89 */
90 private static final class SystemPropertiesStrLookup extends StrLookup<String> {
91
92 /**
93 * {@inheritDoc} This implementation directly accesses system properties.
94 */
95 @Override
96 public String lookup(final String key) {
97 return SystemProperties.getProperty(key);
98 }
99 }
100
101 /**
102 * Lookup that always returns null.
103 */
104 private static final StrLookup<String> NONE_LOOKUP = new MapStrLookup<>(null);
105
106 /**
107 * Lookup based on system properties.
108 */
109 private static final StrLookup<String> SYSTEM_PROPERTIES_LOOKUP = new SystemPropertiesStrLookup();
110
111 /**
112 * Returns a lookup which looks up values using a map.
113 * <p>
114 * If the map is null, then null will be returned from every lookup.
115 * The map result object is converted to a string using toString().
116 * </p>
117 *
118 * @param <V> the type of the values supported by the lookup.
119 * @param map the map of keys to values, may be null.
120 * @return a lookup using the map, not null.
121 */
122 public static <V> StrLookup<V> mapLookup(final Map<String, V> map) {
123 return new MapStrLookup<>(map);
124 }
125
126 /**
127 * Returns a lookup which always returns null.
128 *
129 * @return a lookup that always returns null, not null.
130 */
131 public static StrLookup<?> noneLookup() {
132 return NONE_LOOKUP;
133 }
134
135 /**
136 * Returns a new lookup which uses a copy of the current
137 * {@link System#getProperties() System properties}.
138 * <p>
139 * If a security manager blocked access to system properties, then null will
140 * be returned from every lookup.
141 * </p>
142 * <p>
143 * If a null key is used, this lookup will throw a NullPointerException.
144 * </p>
145 *
146 * @return a lookup using system properties, not null.
147 */
148 public static StrLookup<String> systemPropertiesLookup() {
149 return SYSTEM_PROPERTIES_LOOKUP;
150 }
151
152 /**
153 * Constructs a new instance.
154 */
155 protected StrLookup() {
156 }
157
158 /**
159 * Looks up a String key to a String value.
160 * <p>
161 * The internal implementation may use any mechanism to return the value.
162 * The simplest implementation is to use a Map. However, virtually any
163 * implementation is possible.
164 * </p>
165 * <p>
166 * For example, it would be possible to implement a lookup that used the
167 * key as a primary key, and looked up the value on demand from the database
168 * Or, a numeric based implementation could be created that treats the key
169 * as an integer, increments the value and return the result as a string -
170 * converting 1 to 2, 15 to 16 etc.
171 * </p>
172 * <p>
173 * The {@link #lookup(String)} method always returns a String, regardless of
174 * the underlying data, by converting it as necessary. For example:
175 * </p>
176 * <pre>{@code
177 * Map<String, Object> map = new HashMap<String, Object>();
178 * map.put("number", Integer.valueOf(2));
179 * assertEquals("2", StrLookup.mapLookup(map).lookup("number"));
180 * }</pre>
181 *
182 * @param key the key to be looked up, may be null.
183 * @return the matching value, null if no match.
184 */
185 public abstract String lookup(String key);
186 }