背景

Q：今天遇到一个场景，我们业务需要使用批量的数据进行操作，但是别人的接口只支持一个一个的查，所以需要用多线程去查结果值组装成一个list再进行后期的业务逻辑实现。

实验

用哪个list呢？写了一个小demo

1. ArrayList

使用我们平常经常用的ArrayList进行测试

public class SetThread implements Runnable {private List<Long> indeLong;public SetThread(List<Long> indeLong) {this.indeLong = indeLong;}@Overridepublic void run() {for (int i = 0; i < 50000; i++) {indeLong.add(Long.valueOf(i));}}
}public class MyMain {public static void main(String[] args) throws InterruptedException {// 初始化一个数组List<Long> sycList = new ArrayList<>(200000);SetThread setRunnable1 = new SetThread(sycList);Thread thread1 = new Thread(setRunnable1);SetThread setRunnable2 = new SetThread(sycList);Thread thread2 = new Thread(setRunnable2);SetThread setRunnable3 = new SetThread(sycList);Thread thread3 = new Thread(setRunnable3);SetThread setRunnable5 = new SetThread(sycList);Thread thread5 = new Thread(setRunnable5);thread1.start();thread2.start();thread3.start();thread5.start();thread1.join();      // 主线程等待子线程执行完毕thread2.join();thread3.join();thread5.join();System.out.println(sycList.size());}
}

但是返回的结果值不是我们预期的200000个
在这里插入图片描述

2. synchronizedList

再次使用线程安全的synchronizedList测试

public class MyMain {public static void main(String[] args) throws InterruptedException {// 初始化一个数组List<Long> originList = new ArrayList<>();List<Long> sycList = Collections.synchronizedList(originList);SetThread setRunnable1 = new SetThread(sycList);Thread thread1 = new Thread(setRunnable1);SetThread setRunnable2 = new SetThread(sycList);Thread thread2 = new Thread(setRunnable2);SetThread setRunnable3 = new SetThread(sycList);Thread thread3 = new Thread(setRunnable3);SetThread setRunnable5 = new SetThread(sycList);Thread thread5 = new Thread(setRunnable5);thread1.start();thread2.start();thread3.start();thread5.start();thread1.join();      // 主线程等待子线程执行完毕thread2.join();thread3.join();thread5.join();System.out.println(sycList.size());}
}

使用线程安全的List之后每次执行都是准确返回200000个
在这里插入图片描述

3. 运行抛出异常

中间还有个小插曲，使用ArrayList进行操作不设置最开始的initialCapacity值的测试

public class MyMain {public static void main(String[] args) throws InterruptedException {// 初始化一个数组（不设置数组长度）List<Long> sycList = new ArrayList<>();SetThread setRunnable1 = new SetThread(sycList);Thread thread1 = new Thread(setRunnable1);SetThread setRunnable2 = new SetThread(sycList);Thread thread2 = new Thread(setRunnable2);SetThread setRunnable3 = new SetThread(sycList);Thread thread3 = new Thread(setRunnable3);SetThread setRunnable5 = new SetThread(sycList);Thread thread5 = new Thread(setRunnable5);thread1.start();thread2.start();thread3.start();thread5.start();thread1.join();      // 主线程等待子线程执行完毕thread2.join();thread3.join();thread5.join();System.out.println(sycList.size());}
}

抛出了异常：
在这里插入图片描述