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.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 * <p>
26 * Public access is through {@link StringLookupFactory}.
27 * </p>
28 *
29 * @param <V> A function's input type
30 * @see StringLookupFactory
31 * @since 1.9
32 */
33 final class FunctionStringLookup<V> extends AbstractStringLookup {
34
35 /**
36 * Creates a new instance backed by a Function.
37 *
38 * @param <R> the function's input type
39 * @param function the function, may be null.
40 * @return a new instance backed by the given function.
41 */
42 static <R> FunctionStringLookup<R> on(final Function<String, R> function) {
43 return new FunctionStringLookup<>(function);
44 }
45
46 /**
47 * Creates a new instance backed by a Map. Used by the default lookup.
48 *
49 * @param <V> the map's value type.
50 * @param map the map of keys to values, may be null.
51 * @return a new instance backed by the given map.
52 */
53 static <V> FunctionStringLookup<V> on(final Map<String, V> map) {
54 return on(StringLookupFactory.toMap(map)::get);
55 }
56
57 /**
58 * Function.
59 */
60 private final Function<String, V> function;
61
62 /**
63 * Creates a new instance backed by a Function.
64 *
65 * @param function the function, may be null.
66 */
67 private FunctionStringLookup(final Function<String, V> function) {
68 this.function = function;
69 }
70
71 /**
72 * Looks up a String key by applying the function.
73 * <p>
74 * If the function is null, then null is returned. The function result object is converted to a string using
75 * toString().
76 * </p>
77 *
78 * @param key the key to be looked up, may be null.
79 * @return The function result as a string, may be null.
80 */
81 @Override
82 public String lookup(final String key) {
83 if (function == null) {
84 return null;
85 }
86 final V obj;
87 try {
88 obj = function.apply(key);
89 } catch (final SecurityException | NullPointerException | IllegalArgumentException e) {
90 // Squelched. All lookup(String) will return null.
91 // Could be a ConcurrentHashMap and a null key request
92 return null;
93 }
94 return Objects.toString(obj, null);
95 }
96
97 @Override
98 public String toString() {
99 return super.toString() + " [function=" + function + "]";
100 }
101
102 }