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
18 package org.apache.commons.text.lookup;
19
20 import java.util.function.UnaryOperator;
21
22 /**
23 * Lookups a String key for a String value.
24 * <p>
25 * This class represents the simplest form of a string to string map. It has a benefit over a map in that it can create
26 * the result on demand based on the key.
27 * </p>
28 * <p>
29 * For example, it would be possible to implement a lookup that used the key as a primary key, and looked up the value
30 * on demand from the database.
31 * </p>
32 *
33 * @since 1.3
34 */
35 @FunctionalInterface
36 public interface StringLookup extends UnaryOperator<String> {
37
38 /**
39 * Looks up a String key to provide a String value.
40 * <p>
41 * The internal implementation may use any mechanism to return the value. The simplest implementation is to use a
42 * Map. However, virtually any implementation is possible.
43 * </p>
44 * <p>
45 * For example, it would be possible to implement a lookup that used the key as a primary key, and looked up the
46 * value on demand from the database Or, a numeric based implementation could be created that treats the key as an
47 * integer, increments the value and return the result as a string - converting 1 to 2, 15 to 16 etc.
48 * </p>
49 * <p>
50 * This method always returns a String, regardless of the underlying data, by converting it as necessary. For
51 * example:
52 * </p>
53 *
54 * <pre>
55 * Map<String, Object> map = new HashMap<String, Object>();
56 * map.put("number", Integer.valueOf(2));
57 * assertEquals("2", StringLookupFactory.mapStringLookup(map).lookup("number"));
58 * </pre>
59 *
60 * @param key the key to look up, may be null.
61 * @return The matching value, null if no match.
62 * @since 1.14.0
63 */
64 @Override
65 default String apply(final String key) {
66 return lookup(key);
67 }
68
69 /**
70 * Looks up a String key to provide a String value.
71 * <p>
72 * The internal implementation may use any mechanism to return the value. The simplest implementation is to use a
73 * Map. However, virtually any implementation is possible.
74 * </p>
75 * <p>
76 * For example, it would be possible to implement a lookup that used the key as a primary key, and looked up the
77 * value on demand from the database Or, a numeric based implementation could be created that treats the key as an
78 * integer, increments the value and return the result as a string - converting 1 to 2, 15 to 16 etc.
79 * </p>
80 * <p>
81 * This method always returns a String, regardless of the underlying data, by converting it as necessary. For
82 * example:
83 * </p>
84 *
85 * <pre>
86 * Map<String, Object> map = new HashMap<String, Object>();
87 * map.put("number", Integer.valueOf(2));
88 * assertEquals("2", StringLookupFactory.mapStringLookup(map).lookup("number"));
89 * </pre>
90 *
91 * @param key the key to look up, may be null.
92 * @return The matching value, null if no match.
93 * @deprecated Use {@link #apply(String)}.
94 */
95 @Deprecated
96 String lookup(String key);
97 }