前幾天工作中一段業(yè)務(wù)代碼需要一個(gè)變量每天從1開(kāi)始遞增。為此自己簡(jiǎn)單的封裝了一個(gè)線程安全的計(jì)數(shù)器，可以讓一個(gè)變量每天從1開(kāi)始遞增。當(dāng)然了，如果項(xiàng)目在運(yùn)行中發(fā)生重啟，即便日期還是當(dāng)天，還是會(huì)從1開(kāi)始重新計(jì)數(shù)。所以把計(jì)數(shù)器的值存儲(chǔ)在數(shù)據(jù)庫(kù)中會(huì)更靠譜，不過(guò)這不影響這段代碼的價(jià)值，現(xiàn)在貼出來(lái)，供有需要的人參考。
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
|
package com.hikvision.cms.rvs.common.util;import java.text.SimpleDateFormat;import java.util.ArrayList;import java.util.Date;import java.util.List;import java.util.concurrent.CountDownLatch;import java.util.concurrent.atomic.AtomicInteger;import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;/** * Created by lihong10 on 2017/8/9. * 一個(gè)循環(huán)計(jì)數(shù)器，每天從1開(kāi)始計(jì)數(shù)，隔天重置為1。 * 可以創(chuàng)建一個(gè)該類的全局對(duì)象，然后每次使用時(shí)候調(diào)用其get方法即可，可以保證線程安全性 */public class CircularCounter { private static final AtomicReferenceFieldUpdater<CircularCounter, AtomicInteger> valueUpdater = AtomicReferenceFieldUpdater.newUpdater(CircularCounter.class, AtomicInteger.class, "value"); //保證內(nèi)存可見(jiàn)性 private volatile String key; //保證內(nèi)存可見(jiàn)性 private volatile AtomicInteger value; private static final String DATE_PATTERN = "yyyy-MM-dd"; public CircularCounter() { /** * 這里將key設(shè)置為getCurrentDateString() + "sssssssssss" 是為了測(cè)試addAndGet()方法中日期發(fā)生變化的情況 * 正常使用應(yīng)該將key初始化為getCurrentDateString() */ this.key = getCurrentDateString() + "sssssssssss"; this.value = new AtomicInteger(0); } /** * 獲取計(jì)數(shù)器加1以后的值 * * @return */ public Integer addAndGet() { AtomicInteger oldValue = value; AtomicInteger newInteger = new AtomicInteger(0); int newVal = -1; String newDateStr = getCurrentDateString(); //日期一致，計(jì)數(shù)器加1后返回 if (isDateEquals(newDateStr)) { newVal = add(1); return newVal; } //日期不一致，保證有一個(gè)線程重置技術(shù)器 reSet(oldValue, newInteger, newDateStr); this.key = newDateStr; //重置后加1返回 newVal = add(1); return newVal; } /** * 獲取計(jì)數(shù)器的當(dāng)前值 * @return */ public Integer get() { return value.get(); } /** * 判斷當(dāng)前日期與老的日期（也即key成員變量記錄的值）是否一致 * * @return */ private boolean isDateEquals(String newDateStr) { String oldDateStr = key; if (!isBlank(oldDateStr) && oldDateStr.equals(newDateStr)) { return true; } return false; } /** * 如果日期發(fā)生變化，重置計(jì)數(shù)器，也即將key設(shè)置為當(dāng)前日期，并將value重置為0，重置后才能接著累加， */ private void reSet(AtomicInteger oldValue, AtomicInteger newValue, String newDateStr) { if(valueUpdater.compareAndSet(this, oldValue, newValue)) { System.out.println("線程" + Thread.currentThread().getName() + "發(fā)現(xiàn)日期發(fā)生變化"); } } /** * 獲取當(dāng)前日期字符串 * * @return */ private String getCurrentDateString() { Date date = new Date(); String newDateStr = new SimpleDateFormat(DATE_PATTERN).format(date); return newDateStr; } /** * 計(jì)數(shù)器的值加1。采用CAS保證線程安全性 * * @param increment */ private int add(int increment) { return value.addAndGet(increment); } public static boolean isBlank(CharSequence cs) { int strLen; if(cs != null && (strLen = cs.length()) != 0) { for(int i = 0; i < strLen; ++i) { if(!Character.isWhitespace(cs.charAt(i))) { return false; } } return true; } else { return true; } } public static void test() { CircularCounter c = new CircularCounter(); AtomicInteger count = new AtomicInteger(0); List<Thread> li = new ArrayList<Thread>(); int size = 10; CountDownLatch latch1 = new CountDownLatch(1); CountDownLatch latch2 = new CountDownLatch(size); for (int i = 0; i < size; i++) { Thread t = new Thread(new CounterRunner(c, latch1, latch2, count), "thread-" + i); li.add(t); t.start(); } System.out.println("start"); latch1.countDown(); try { latch2.await(); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println(count.get()); System.out.println(c.get()); if(count.get() == c.get()) { System.out.println("該計(jì)數(shù)器是線程安全的！！！"); } } public static void main(String... args) { for(int i = 0; i < 15; i++) { test(); } }}/** * 測(cè)試使用的Runnable對(duì)象 */class CounterRunner implements Runnable { private CircularCounter counter; private CountDownLatch latch1; private CountDownLatch latch2; private AtomicInteger count; public CounterRunner(CircularCounter counter, CountDownLatch latch1, CountDownLatch latch2, AtomicInteger count) { this.latch1 = latch1; this.latch2 = latch2; this.counter = counter; this.count = count; } @Override public void run() { try { latch1.await(); System.out.println("****************"); for (int i = 0; i < 20; i++) { counter.addAndGet(); count.addAndGet(1); } latch2.countDown(); } catch (InterruptedException e) { e.printStackTrace(); } }} |
總結(jié)
以上就是本文關(guān)于Java線程安全的計(jì)數(shù)器簡(jiǎn)單實(shí)現(xiàn)代碼示例的內(nèi)容，希望對(duì)大家有所幫助，有什么問(wèn)題可以隨時(shí)留言，歡迎大家一起交流討論。感謝朋友們對(duì)服務(wù)器之家網(wǎng)站的支持！
原文鏈接：http://blog.csdn.net/nmgrd/article/details/77015206
