Method: LazySupplier(Supplier)

1: /*
2: * *********************************************************************************************************************
3: *
4: * TheseFoolishThings: Miscellaneous utilities
5: * http://tidalwave.it/projects/thesefoolishthings
6: *
7: * Copyright (C) 2009 - 2023 by Tidalwave s.a.s. (http://tidalwave.it)
8: *
9: * *********************************************************************************************************************
10: *
11: * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
12: * the License. You may obtain a copy of the License at
13: *
14: * http://www.apache.org/licenses/LICENSE-2.0
15: *
16: * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
17: * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
18: * specific language governing permissions and limitations under the License.
19: *
20: * *********************************************************************************************************************
21: *
22: * git clone https://bitbucket.org/tidalwave/thesefoolishthings-src
23: * git clone https://github.com/tidalwave-it/thesefoolishthings-src
24: *
25: * *********************************************************************************************************************
26: */
27: package it.tidalwave.util;
28:
29: import javax.annotation.Nonnull;
30: import javax.annotation.concurrent.ThreadSafe;
31: import java.util.function.Supplier;
32: import it.tidalwave.util.annotation.VisibleForTesting;
33: import lombok.RequiredArgsConstructor;
34:
35: /***********************************************************************************************************************
36: *
37: * A supplier of an object that is lazily evaluated (when its value is requested for the first time). It warranties
38: * that the real wrapped supplier is called only once.
39: *
40: * @author Fabrizio Giudici
41: * @since 3.2-ALPHA-13
42: *
43: **********************************************************************************************************************/
44:•@ThreadSafe @RequiredArgsConstructor(staticName = "of")
45: public class LazySupplier<T> implements Supplier<T>
46: {
47: @Nonnull
48: private final Supplier<T> supplier;
49:
50: @VisibleForTesting volatile T ref = null;
51:
52: /** {@inheritDoc} */
53: @Override @Nonnull
54: public synchronized T get()
55: {
56: // AtomicReference.updateAndGet() not good because in case of contention it might call supplier multiple times
57: // We don't mess with double check for null since nowadays synchronized is fast
58: if (ref == null)
59: {
60: ref = supplier.get();
61: }
62:
63: return ref;
64: }
65:
66: public synchronized void clear()
67: {
68: ref = null;
69: }
70:
71: public void set (@Nonnull final T ref)
72: {
73: this.ref = ref;
74: }
75: }