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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    *      http://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  
21  /**
22   * Lookup a String key to a String value.
23   * <p>
24   * This class represents the simplest form of a string to string map.
25   * It has a benefit over a map in that it can create the result on
26   * demand based on the key.
27   * <p>
28   * This class comes complete with various factory methods.
29   * If these do not suffice, you can subclass and implement your own matcher.
30   * <p>
31   * For example, it would be possible to implement a lookup that used the
32   * key as a primary key, and looked up the value on demand from the database
33   *
34   * @since 2.2
35   * @deprecated as of 3.6, use commons-text
36   * <a href="https://commons.apache.org/proper/commons-text/javadocs/api-release/org/apache/commons/text/StrLookup.html">
37   * StrLookup</a> instead
38   */
39  @Deprecated
40  public abstract class StrLookup<V> {
41  
42      /**
43       * Lookup that always returns null.
44       */
45      private static final StrLookup<String> NONE_LOOKUP = new MapStrLookup<>(null);
46  
47      /**
48       * Lookup based on system properties.
49       */
50      private static final StrLookup<String> SYSTEM_PROPERTIES_LOOKUP = new SystemPropertiesStrLookup();
51  
52      //-----------------------------------------------------------------------
53      /**
54       * Returns a lookup which always returns null.
55       *
56       * @return a lookup that always returns null, not null
57       */
58      public static StrLookup<?> noneLookup() {
59          return NONE_LOOKUP;
60      }
61  
62      /**
63       * Returns a new lookup which uses a copy of the current
64       * {@link System#getProperties() System properties}.
65       * <p>
66       * If a security manager blocked access to system properties, then null will
67       * be returned from every lookup.
68       * <p>
69       * If a null key is used, this lookup will throw a NullPointerException.
70       *
71       * @return a lookup using system properties, not null
72       */
73      public static StrLookup<String> systemPropertiesLookup() {
74          return SYSTEM_PROPERTIES_LOOKUP;
75      }
76  
77      /**
78       * Returns a lookup which looks up values using a map.
79       * <p>
80       * If the map is null, then null will be returned from every lookup.
81       * The map result object is converted to a string using toString().
82       *
83       * @param <V> the type of the values supported by the lookup
84       * @param map  the map of keys to values, may be null
85       * @return a lookup using the map, not null
86       */
87      public static <V> StrLookup<V> mapLookup(final Map<String, V> map) {
88          return new MapStrLookup<>(map);
89      }
90  
91      //-----------------------------------------------------------------------
92      /**
93       * Constructor.
94       */
95      protected StrLookup() {
96          super();
97      }
98  
99      /**
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.length() > 0) {
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 }