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.text.lookup;
18
19 import java.util.Map;
20 import java.util.Objects;
21 import java.util.function.Function;
22
23 /**
24 * A function-based lookup where the request for a lookup is answered by applying that function with a key.
25 *
26 * @param <V> A function's input type
27 * @since 1.9
28 */
29 final class FunctionStringLookup<V> extends AbstractStringLookup {
30
31 /**
32 * Creates a new instance backed by a Function.
33 *
34 * @param <R> the function's input type
35 * @param function the function, may be null.
36 * @return a new instance backed by the given function.
37 */
38 static <R> FunctionStringLookup<R> on(final Function<String, R> function) {
39 return new FunctionStringLookup<>(function);
40 }
41
42 /**
43 * Creates a new instance backed by a Map. Used by the default lookup.
44 *
45 * @param <V> the map's value type.
46 * @param map the map of keys to values, may be null.
47 * @return a new instance backed by the given map.
48 */
49 static <V> FunctionStringLookup<V> on(final Map<String, V> map) {
50 return on(StringLookupFactory.toMap(map)::get);
51 }
52
53 /**
54 * Function.
55 */
56 private final Function<String, V> function;
57
58 /**
59 * Creates a new instance backed by a Function.
60 *
61 * @param function the function, may be null.
62 */
63 private FunctionStringLookup(final Function<String, V> function) {
64 this.function = function;
65 }
66
67 /**
68 * Looks up a String key by applying the function.
69 * <p>
70 * If the function is null, then null is returned. The function result object is converted to a string using
71 * toString().
72 * </p>
73 *
74 * @param key the key to be looked up, may be null.
75 * @return The function result as a string, may be null.
76 */
77 @Override
78 public String lookup(final String key) {
79 if (function == null) {
80 return null;
81 }
82 final V obj;
83 try {
84 obj = function.apply(key);
85 } catch (final SecurityException | NullPointerException | IllegalArgumentException e) {
86 // Squelched. All lookup(String) will return null.
87 // Could be a ConcurrentHashMap and a null key request
88 return null;
89 }
90 return Objects.toString(obj, null);
91 }
92
93 @Override
94 public String toString() {
95 return super.toString() + " [function=" + function + "]";
96 }
97
98 }