一个线程安全的计数器实现(java)，可以让一个变量每天从1开始递增

前几天工作中一段业务代码需要一个变量每天从1开始递增。为此自己简单的封装了一个线程安全的计数器，可以让一个变量每天从1开始递增。当然了，如果项目在运行中发生重启，即便日期还是当天，还是会从1开始重新计数。所以把计数器的值存储在数据库中会更靠谱，不过这不影响这段代码的价值，现在贴出来，供有需要的人参考。

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.
* 一个循环计数器，每天从1开始计数，隔天重置为1。
* 可以创建一个该类的全局对象，然后每次使用时候调用其get方法即可，可以保证线程安全性
*/
public class CircularCounter {

private static final AtomicReferenceFieldUpdater<CircularCounter, AtomicInteger> valueUpdater =
AtomicReferenceFieldUpdater.newUpdater(CircularCounter.class, AtomicInteger.class, "value");
//保证内存可见性
private volatile String key;
//保证内存可见性
private volatile AtomicInteger value;
private static final String DATE_PATTERN = "yyyy-MM-dd";

public CircularCounter() {
/**
* 这里将key设置为getCurrentDateString() + "sssssssssss" 是为了测试addAndGet()方法中日期发生变化的情况
* 正常使用应该将key初始化为getCurrentDateString()
*/
this.key = getCurrentDateString() + "sssssssssss";
this.value = new AtomicInteger(0);
}

/**
* 获取计数器加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，计数器加1后返回
if (isDateEquals(newDateStr)) {
newVal = add(1);
return newVal;
}

//日期不一致，保证有一个线程重置技术器
reSet(oldValue, newInteger, newDateStr);
this.key = newDateStr;
//重置后加1返回
newVal = add(1);
return newVal;
}

/**
* 获取计数器的当前值
* @return
*/
public Integer get() {
return value.get();
}

/**
* 判断当前日期与老的日期（也即key成员变量记录的值）是否一致
*
* @return
*/
private boolean isDateEquals(String newDateStr) {
String oldDateStr = key;
if (!isBlank(oldDateStr) && oldDateStr.equals(newDateStr)) {
return true;
}

return false;
}

/**
* 如果日期发生变化，重置计数器，也即将key设置为当前日期，并将value重置为0，重置后才能接着累加，
*/
private void reSet(AtomicInteger oldValue, AtomicInteger newValue, String newDateStr) {
if(valueUpdater.compareAndSet(this, oldValue, newValue)) {
System.out.println("线程" + Thread.currentThread().getName() + "发现日期发生变化");
}
}

/**
* 获取当前日期字符串
*
* @return
*/
private String getCurrentDateString() {
Date date = new Date();
String newDateStr = new SimpleDateFormat(DATE_PATTERN).format(date);
return newDateStr;
}

/**
* 计数器的值加1。采用CAS保证线程安全性
*
* @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("该计数器是线程安全的！！！");
}

}

public static void main(String... args) {
for(int i = 0; i < 15; i++) {
test();
}
}

}

/**
* 测试使用的Runnable对象
*/
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();
}
}
}