转 https://blog.csdn.net/weixin_43893397/article/details/104361154

【1】代码示例 

/*** 线程池测试-自定义线程池创建方式* @since 2021/03/23 */
public class ThreadPoolMain2 {public static void main(String[] args) throws Exception {newMethod();}public static void newMethod() throws InterruptedException {/*** 开启一个线程池  默认线程是10个* 使用默认线程工厂* 拒绝策略为CallerRunsPolicy策略，让后面的线程先等待 */ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(10, 10, 1000L, TimeUnit.MILLISECONDS, new ArrayBlockingQueue<Runnable>(10),Executors.defaultThreadFactory(),new ThreadPoolExecutor.CallerRunsPolicy());//书写一个循环  模拟100个用户同时访问for (int request = 0; request< 100;request ++){final int temp = request; //开启一个线程threadPoolExecutor.execute(() ->{System.out.println("任务" + temp +"开始执行...");/*** 睡10秒 */try {Thread.sleep(1000L * 3);} catch (InterruptedException e) {e.printStackTrace();}System.out.println("任务" + temp +"执行结束...");});}}
}

【2】 ThreadPoolExecutor 构造器解析

/*** Creates a new {@code ThreadPoolExecutor} with the given initial* parameters.** @param corePoolSize the number of threads to keep in the pool, even*        if they are idle, unless {@code allowCoreThreadTimeOut} is set* @param maximumPoolSize the maximum number of threads to allow in the*        pool* @param keepAliveTime when the number of threads is greater than*        the core, this is the maximum time that excess idle threads*        will wait for new tasks before terminating.* @param unit the time unit for the {@code keepAliveTime} argument* @param workQueue the queue to use for holding tasks before they are*        executed.  This queue will hold only the {@code Runnable}*        tasks submitted by the {@code execute} method.* @param threadFactory the factory to use when the executor*        creates a new thread* @param handler the handler to use when execution is blocked*        because the thread bounds and queue capacities are reached* @throws IllegalArgumentException if one of the following holds:<br>*         {@code corePoolSize < 0}<br>*         {@code keepAliveTime < 0}<br>*         {@code maximumPoolSize <= 0}<br>*         {@code maximumPoolSize < corePoolSize}* @throws NullPointerException if {@code workQueue}*         or {@code threadFactory} or {@code handler} is null*/public ThreadPoolExecutor(int corePoolSize,int maximumPoolSize,long keepAliveTime,TimeUnit unit,BlockingQueue<Runnable> workQueue,ThreadFactory threadFactory,RejectedExecutionHandler handler) {

【3】参数解析

序号	参数名	描述	中文
1	corePoolSize	the number of threads to keep in the pool, even if they are idle, unless {@code allowCoreThreadTimeOut} is set.	除非设置了{@code allowCoreThreadTimeOut}，否则即使它们处于空闲状态也要保留在池中的线程数。
2	maximumPoolSize	the maximum number of threads to allow in the pool	池中允许的最大线程数
3	keepAliveTime	when the number of threads is greater than the core, this is the maximum time that excess idle threads will wait for new tasks before terminating.	当线程数大于内核数时，这是多余的空闲线程将在终止之前等待新任务的最长时间。
4	unit	the time unit for the {@code keepAliveTime} argument	{@code keepAliveTime}参数的时间单位
5	workQueue	the queue to use for holding tasks before they are executed. This queue will hold only the Runnable tasks submitted by the execute method.	在执行任务之前用于保留任务的队列。 此队列将仅保存execute方法提交的Runnable任务。
6	threadFactory	the factory to use when the executorcreates a new thread.	执行程序创建新线程时要使用的工厂。
7	handler	the handler to use when execution is blockedbecause the thread bounds and queue capacities are reached.	当执行被阻塞时使用的处理程序，因为达到了线程界限和队列容量。

【4】抛弃策略

// 当任务无法添加到阻塞队列时的处理策略-直接抛出异常RejectedExecutionHandler rejectHandler1 = new ThreadPoolExecutor.AbortPolicy(); // -会调用当前线程池的所在的线程去执行被拒绝的任务。RejectedExecutionHandler rejectHandler2 = new ThreadPoolExecutor.CallerRunsPolicy(); // 会抛弃任务队列中最旧的任务也就是最先加入队列的，再把这个新任务添加进去。RejectedExecutionHandler rejectHandler3 = new ThreadPoolExecutor.DiscardOldestPolicy();// 会让被线程池拒绝的任务直接抛弃，不会抛异常也不会执行。RejectedExecutionHandler rejectHandler4 = new ThreadPoolExecutor.DiscardPolicy(); RejectedExecutionHandler rejectHandler = rejectHandler4; ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(10, 10, 1000L, TimeUnit.MILLISECONDS, new ArrayBlockingQueue<Runnable>(10),Executors.defaultThreadFactory(), rejectHandler);