线程池动态修改核心线程数

通过线程池的方法重新设置核心线程数 setCorePoolSize

当最新的核心线程数小于之前的核心线程数时，则需要进行多余的线程中断

当最新的核心线程数大于之前的核心线程数，则需要逐步的增加核心线程数

源码如下：

 public void setCorePoolSize(int corePoolSize) {
        if (corePoolSize < 0)
            throw new IllegalArgumentException();
        int delta = corePoolSize - this.corePoolSize;
        this.corePoolSize = corePoolSize;
        if (workerCountOf(ctl.get()) > corePoolSize)
            interruptIdleWorkers();
        else if (delta > 0) {
            // We don't really know how many new threads are "needed".
            // As a heuristic, prestart enough new workers (up to new
            // core size) to handle the current number of tasks in
            // queue, but stop if queue becomes empty while doing so.
            int k = Math.min(delta, workQueue.size());
            while (k-- > 0 && addWorker(null, true)) {
                if (workQueue.isEmpty())
                    break;
            }
        }
    }

 备注：当最新的核心线程数大于之前核心线程数时，不是一致性增加差额的线程数，而是一个一个线程添加，添加完一个再去查询任务队列是否有任务；有任务则再次添加，没有任务则就此停止