putIfAbsent 灵活运用
使用场景
同一个方法只能允许同一个用户进入一次，只有运行完了之后，再允许进入。
不过是多台机器，此方式不适合，要使用分布式锁，比如使用zookeeper进行实现
测试类如下：
import org.apache.commons.lang3.RandomStringUtils;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CountDownLatch;
/**
* Created by cailu on 2018/6/6.
*/
public class Test{
public static final ConcurrentHashMap cache = new ConcurrentHashMap();
public static void main(String[] args) throws InterruptedException {
CountDownLatch start = new CountDownLatch(1);
CountDownLatch stop = new CountDownLatch(10);
for (int i = 0; i < 10; i++) {
RunThread runThread = new RunThread(RandomStringUtils.random(1, "ABC"), start, stop);
Thread thread = new Thread(runThread);
thread.start();
}
start.countDown();
stop.await();
System.out.println("全部运行完毕");
}
static class RunThread implements Runnable {
private String userid;
private CountDownLatch start;
private CountDownLatch stop;
public RunThread(String userid, CountDownLatch start, CountDownLatch stop) {
this.userid = userid;
this.start = start;
this.stop = stop;
}
public void run() {
try {
start.await();
RunMethod.method(userid);
} catch (InterruptedException e) {
e.printStackTrace();
}finally {
stop.countDown();
}
}
}
static class RunMethod{
public static void method(String userid) {
Integer key = cache.putIfAbsent(userid, 1);
if (key != null) {
System.out.println(userid + "|操作频繁，稍后重试");
return;
}
try {
System.out.println(userid+"|运行开始");
try {
Thread.sleep(1*100);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(userid+"|运行结束");
} catch (Exception e) {
e.printStackTrace();
}finally {
cache.remove(userid);
}
}
}
}
测试结果如下：
B|运行开始
C|运行开始
B|操作频繁，稍后重试
A|运行开始
B|操作频繁，稍后重试
B|操作频繁，稍后重试
C|操作频繁，稍后重试
A|操作频繁，稍后重试
C|操作频繁，稍后重试
B|操作频繁，稍后重试
C|运行结束
B|运行结束
A|运行结束
全部运行完毕
