java 线程池 Executors，ExecutorService

1，线程池对象

1，Executors 工厂类

• 方法 newFixedThreadPool(int num)，创建固定个数线程池，num 代表线程个数

• 方法 newCachedThreadPool()，创建弹性个数的线程池，当忙碌时，会不断创建线程，当空闲时，会回收线程

2，ExecutorService 线程池

3，线程计数器 CountDownLatch

• new CountDownLatch(10)，一般实例化会传入具体等待几个线程
• countDownLatch.countDown()，会把传入的值 减一，当数字是 0 的时候会继续往下执行
• countDownLatch.await(60, TimeUnit.HOURS) ，等待countDownLatch.countDown()将传入的值减到0，当超时的时候也会继续往下执行

2，简单的使用

package com.hwq.admin.back.service;

import com.hwq.common.exception.ServerException;
import org.springframework.stereotype.Service;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

@Service
public class ThreadPoolService {

    private final ExecutorService executorService = Executors.newFixedThreadPool(5);

    public List<String> listPoolName() {
        CountDownLatch countDownLatch = new CountDownLatch(10);
        List<String> list = new ArrayList<>();
        List<String> synList = Collections.synchronizedList(list);  // 注意线程安全
        for (int i = 0; i < 10; i++) {
            executorService.execute(() -> {
                try {
                    Thread.sleep(1000);
                    Thread t = Thread.currentThread();
                    synList.add(t.getId() + " : " + t.getName());
                    countDownLatch.countDown();           // 通知计数器完成任务
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            });
        }

        try {
            countDownLatch.await(60, TimeUnit.SECONDS);   // 线程等待
            return list;
        } catch (InterruptedException ex) {
            throw new ServerException(ex);
        }
    }
}