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
18 package org.apache.commons.lang3.function;
19
20 import java.util.Objects;
21 import java.util.function.Function;
22
23 /**
24 * A functional interface like {@link Function} that declares a {@link Throwable}.
25 *
26 * @param <T> Input type 1.
27 * @param <R> Return type.
28 * @param <E> The kind of thrown exception or error.
29 * @since 3.11
30 */
31 @FunctionalInterface
32 public interface FailableFunction<T, R, E extends Throwable> {
33
34 /** NOP singleton */
35 @SuppressWarnings("rawtypes")
36 FailableFunction NOP = t -> null;
37
38 /**
39 * Starts a fluent chain like {@code function(foo::bar).andThen(...).andThen(...).apply(...);}
40 *
41 * @param <T> Input type.
42 * @param <R> Return type.
43 * @param <E> The kind of thrown exception or error.
44 * @param function the argument to return.
45 * @return the argument
46 * @since 3.14.0
47 */
48 static <T, R, E extends Throwable> FailableFunction<T, R, E> function(final FailableFunction<T, R, E> function) {
49 return function;
50 }
51
52 /**
53 * Returns a function that always returns its input argument.
54 *
55 * @param <T> the type of the input and output objects to the function
56 * @param <E> The kind of thrown exception or error.
57 * @return a function that always returns its input argument
58 */
59 static <T, E extends Throwable> FailableFunction<T, T, E> identity() {
60 return t -> t;
61 }
62
63 /**
64 * Returns The NOP singleton.
65 *
66 * @param <T> Consumed type.
67 * @param <R> Return type.
68 * @param <E> The kind of thrown exception or error.
69 * @return The NOP singleton.
70 */
71 @SuppressWarnings("unchecked")
72 static <T, R, E extends Throwable> FailableFunction<T, R, E> nop() {
73 return NOP;
74 }
75
76 /**
77 * Returns a composed {@link FailableFunction} like {@link Function#andThen(Function)}.
78 *
79 * @param <V> the output type of the {@code after} function, and of the composed function.
80 * @return a composed {@link FailableFunction} like {@link Function#andThen(Function)}.
81 * @param after the operation to perform after this one.
82 * @throws NullPointerException when {@code after} is null.
83 */
84 default <V> FailableFunction<T, V, E> andThen(final FailableFunction<? super R, ? extends V, E> after) {
85 Objects.requireNonNull(after);
86 return (final T t) -> after.apply(apply(t));
87 }
88
89 /**
90 * Applies this function.
91 *
92 * @param input the input for the function
93 * @return the result of the function
94 * @throws E Thrown when the function fails.
95 */
96 R apply(T input) throws E;
97
98 /**
99 * Returns a composed {@link FailableFunction} like {@link Function#compose(Function)}.
100 *
101 * @param <V> the input type to the {@code before} function, and to the composed function.
102 * @param before the operator to apply before this one.
103 * @return a composed {@link FailableFunction} like {@link Function#compose(Function)}.
104 * @throws NullPointerException if before is null.
105 * @see #andThen(FailableFunction)
106 */
107 default <V> FailableFunction<V, R, E> compose(final FailableFunction<? super V, ? extends T, E> before) {
108 Objects.requireNonNull(before);
109 return (final V v) -> apply(before.apply(v));
110 }
111 }