线程池+CountDownLatch 处理大集合

场景：有一个需求：首先从数据库中取出上千条数据，然后需要逐条对数据进行分析，例如分析情感/是否重复等多项分析。

解决：将取出来的上千条，分批+多线程处理。

public class CountDownLatchTest {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<String>();
        for (int i = 0; i < 1000; i++) {
            list.add(String.valueOf(i));
        }


//        int processors = Runtime.getRuntime().availableProcessors();
        ExecutorService threadPool = Executors.newFixedThreadPool(10);


        final CountDownLatch latch = new CountDownLatch(10);

        List<List<String>> splitList = averageAssign(list, 10);

        for (int i = 0; i < splitList.size(); i++) {
            final List<String> temp = splitList.get(i);
            threadPool.execute(() -> {
                Runnable runnable = new Runnable() {

                   @Override
                    public void run() {
//这里可能有坑，要注意 countDown()一定要执行完 ！！！
                        for (int j = 0; j < temp.size(); j++) {
                            System.out.println("内部for执行");
                        }
                        System.out.println("子线程" + Thread.currentThread().getName() + "执行完成"+temp);
                        latch.countDown();//当前线程调用此方法，则计数减一
                    }

                };
                threadPool.execute(runnable);

            });

        }


        try {
            latch.await();//阻塞当前线程，直到计数器的值为0
            System.out.println("10 end ");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }finally {
            threadPool.shutdown();
        }



    }


    /**
     * 将一组数据平均分成n组
     *
     * @param source 要分组的数据源
     * @param n      平均分成n组
     * @param <T>
     * @return
     */
    public static <T> List<List<T>> averageAssign(List<T> source, int n) {
        List<List<T>> result = new ArrayList<List<T>>();
        int remainder = source.size() % n;  //(先计算出余数)
        int number = source.size() / n;  //然后是商
        int offset = 0;//偏移量
        for (int i = 0; i < n; i++) {
            List<T> value = null;
            if (remainder > 0) {
                value = source.subList(i * number + offset, (i + 1) * number + offset + 1);
                remainder--;
                offset++;
            } else {
                value = source.subList(i * number + offset, (i + 1) * number + offset);
            }
            result.add(value);
        }
        return result;
    }


    /**
     * 将集合按len数量分成若干个list
     *
     * @param list
     * @param len  每个集合的数量
     * @return
     */
    public static List<List<String>> splitList(List<String> list, int len) {
        if (list == null || list.size() == 0 || len < 1) {
            return null;
        }
        List<List<String>> result = new ArrayList<List<String>>();

        int size = list.size();
        int count = (size + len - 1) / len;

        for (int i = 0; i < count; i++) {
            List<String> subList = list.subList(i * len, ((i + 1) * len > size ? size : len * (i + 1)));

            result.add(subList);
        }
        return result;
    }

}