示例模拟10000次请求，每次并发数为100，每次请求，计数器加1,最后输出计数器值。
上代码：

package concurrent;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;

/**
 * @Auther：zhl
 * @Date：2019/7/13
 * @Description： 并发测试
 */
public class ConcurrentSample {
    //并发线程数量
    private static int users = 100;
    //访问次数
    private static int count = 10000;
    //访问总量
    private static int number = 0;

    public static void main(String[] args) {
        //定义线程池
        ExecutorService executorService = Executors.newCachedThreadPool();
        //并发量
        Semaphore semaphore = new Semaphore(users);
        for (int i = 0; i < count; i++) {
            executorService.execute(() -> {
                try {
                    semaphore.acquire();
                    add();
                    semaphore.release();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            });
        }
        try {
            Thread.sleep(3000);
        } catch (Exception e) {
            e.printStackTrace();
        }
        executorService.shutdown();
        System.out.println(number);
    }
    public static void add() {
        number++;
    }
}

计数器：9997
计数器：10000
计数器：9997
每次输出结果不一致，这都是并发导致的