Java线程安全的计数器简单实现代码示例

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;

public class CircularCounter {
  private static final AtomicReferenceFieldUpdater 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() {
    
    this.key = getCurrentDateString() + "sssssssssss";
    this.value = new AtomicInteger(0);
  }
  
  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;
  }
  
  public Integer get() {
    return value.get();
  }
  
  private boolean isDateEquals(String newDateStr) {
    String oldDateStr = key;
    if (!isBlank(oldDateStr) && oldDateStr.equals(newDateStr)) {
      return true;
    }
    return false;
  }
  
  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");
    }
  }
  
  private String getCurrentDateString() {
    Date date = new Date();
    String newDateStr = new SimpleDateFormat(DATE_PATTERN).format(date);
    return newDateStr;
  }
  
  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 li = new ArrayList();
    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();
    }
  }
}

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();
    }
  }
}

总结

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