java之使用多线程代替for循环(解决主线程提前结束问题)

//参数count为计数值
public CountDownLatch(int count) {};  

// 调用 await() 方法的线程会被挂起，它会等待直到 count 值为 0 才继续执行
public void await() throws InterruptedException {};
 
// 和 await() 类似，若等待 timeout 时长后，count 值还是没有变为 0，不再等待，继续执行
public boolean await(long timeout, TimeUnit unit) throws InterruptedException {};
 
// 会将 count 减 1，直至为 0
public void countDown() {};

import java.util.concurrent.CountDownLatch;
 
/**
 * 让多个线程等待：模拟并发，让并发线程一起执行
 */
public class CountDownLatchTest {
    public static void main(String[] args) throws InterruptedException {
 
        CountDownLatch countDownLatch = new CountDownLatch(1);
        
        for (int i = 0; i < 5; i++) {
            new Thread(() -> {
                try {
                    // 等待
                    countDownLatch.await();
                    String parter = "【" + Thread.currentThread().getName() + "】";
                    System.out.println(parter + "开始执行……");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }).start();
        }
 
        Thread.sleep(2000);
       
        countDownLatch.countDown();
    }
}

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CountDownLatch;
 
/**
 * 让单个线程等待：多个线程(任务)完成后，进行汇总合并
 */
public class CountDownLatchTest3 {
 
    //用于聚合所有的统计指标
    private static Map map = new ConcurrentHashMap();
    //创建计数器，这里需要统计4个指标
    private static CountDownLatch countDownLatch = new CountDownLatch(4);
 
    public static void main(String[] args) throws Exception {
 
        //记录开始时间
        long startTime = System.currentTimeMillis();
 
        Thread countUserThread = new Thread(() -> {
            try {
                System.out.println("正在统计新增用户数量");
                Thread.sleep(3000);//任务执行需要3秒
                map.put("userNumber", 100);//保存结果值
                System.out.println("统计新增用户数量完毕");
                countDownLatch.countDown();//标记已经完成一个任务
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });
        Thread countOrderThread = new Thread(() -> {
            try {
                System.out.println("正在统计订单数量");
                Thread.sleep(3000);//任务执行需要3秒
                map.put("countOrder", 20);//保存结果值
                System.out.println("统计订单数量完毕");
                countDownLatch.countDown();//标记已经完成一个任务
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });
 
        Thread countGoodsThread = new Thread(() -> {
            try {
                System.out.println("正在商品销量");
                Thread.sleep(3000);//任务执行需要3秒
                map.put("countGoods", 300);//保存结果值
                System.out.println("统计商品销量完毕");
                countDownLatch.countDown();//标记已经完成一个任务
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });
 
        Thread countmoneyThread = new Thread(() -> {
            try {
                System.out.println("正在总销售额");
                Thread.sleep(3000);//任务执行需要3秒
                map.put("countMoney", 40000);//保存结果值
                System.out.println("统计销售额完毕");
                countDownLatch.countDown();//标记已经完成一个任务
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });
        
        //启动子线程执行任务
        countUserThread.start();
        countGoodsThread.start();
        countOrderThread.start();
        countmoneyThread.start();
 
        try {
            //主线程等待所有统计指标执行完毕
            countDownLatch.await();
            long endTime = System.currentTimeMillis();//记录结束时间
            System.out.println("------统计指标全部完成--------");
            System.out.println("统计结果为：" + map);
            System.out.println("任务总执行时间为" + (endTime - startTime) + "ms");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
 
    }
}

@Override
    public AppResponse getLocations() throws InterruptedException {
        List<GetLocationVO> vos = new ArrayList<>();
        vos = projectDao.getLocationOne();    
//      原来的代码
//        for (GetLocationVO vo : vos) {
//            List<LocationVO> children = projectDao.getLocationChildren(vo.getId());
//            vo.setChildren(children);
//        }
        //改造后的代码
        Thread(vos,10);
        return AppResponse.success("查询成功",vos);
    }
 
    //此处有加锁
    public synchronized void Thread(List<GetLocationVO> list, int nThread) throws InterruptedException {
        if (CollectionUtils.isEmpty(list) || nThread <= 0 || CollectionUtils.isEmpty(list)) {
            return;
        }
        CountDownLatch latch = new CountDownLatch(list.size());//创建一个计数器（大小为当前数组的大小，确保所有执行完主线程才结束）
        ExecutorService pool = Executors.newFixedThreadPool(nThread);//创建一个固定的线程池
        for (GetLocationVO vo : list) {
            pool.execute(() -> {
                //处理的业务
                List<LocationVO> children = projectDao.getLocationChildren(vo.getId());
                vo.setChildren(children);
                latch.countDown();
            });
        }
        latch.await();
        pool.shutdown();
    }