线程池 线程池线程池：三大方法、7大参数、4种拒绝策略池化技术事先准备好一些资源，要用的时候从池子中取，用完之后还回去优点：降低资源的消耗提高响应速度方便管理三大方法package com.sw.pool; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; /** * @Author suaxi * @Date 2021/2/14 21:23 */ public class PoolTest { public static void main(String[] args) { //ExecutorService pool = Executors.newSingleThreadExecutor(); //单个线程 //ExecutorService pool = Executors.newFixedThreadPool(10); //创建一个固定大小的线程池 ExecutorService pool = Executors.newCachedThreadPool(); //线程池大小可弹性伸缩 try { for (int i = 0; i < 50; i++) { pool.execute(() -> { System.out.println(Thread.currentThread().getName() + "--->Pool Test"); }); } } catch (Exception e) { e.printStackTrace(); } finally { //线程池用完，程序结束，关闭线程池 pool.shutdown(); } } } 七大参数 public ThreadPoolExecutor(int corePoolSize, //核心线程池大小 int maximumPoolSize, //最大线程池大小 long keepAliveTime, //超时后多长时间没人操作就关闭 TimeUnit unit, //超时单位 BlockingQueue<Runnable> workQueue, //阻塞队列 ThreadFactory threadFactory, //线程工厂，用于创建线程 RejectedExecutionHandler handler) { //拒绝策略 if (corePoolSize < 0 || maximumPoolSize <= 0 || maximumPoolSize < corePoolSize || keepAliveTime < 0) throw new IllegalArgumentException(); if (workQueue == null || threadFactory == null || handler == null) throw new NullPointerException(); this.acc = System.getSecurityManager() == null ? null : AccessController.getContext(); this.corePoolSize = corePoolSize; this.maximumPoolSize = maximumPoolSize; this.workQueue = workQueue; this.keepAliveTime = unit.toNanos(keepAliveTime); this.threadFactory = threadFactory; this.handler = handler; }图片来源：狂神说Java手动创建一个线程池package com.sw.pool; import java.util.concurrent.*; /** * @Author suaxi * @Date 2021/2/14 21:23 * 4种拒绝策略： * AbortPolicy() 线程池满了，还有人进来，不处理这个人的请求，同时抛出异常 * CallerRunsPolicy() 哪里来的请求，回到哪里去（请求对应的主方法） * DiscardPolicy() 队列满了，丢掉后来的请求，不抛出异常 * DiscardOldestPolicy() 队列满了，尝试去和最早进行服务的窗口竞争，看那里的服务是否快要结束了，结束就进去提出请求，这种策略也不抛出异常 */ public class ThreadPoolExecutorTest { public static void main(String[] args) { //自定义线程池 ExecutorService pool = new ThreadPoolExecutor( 2, 5, 3, TimeUnit.SECONDS, new LinkedBlockingDeque<>(3), Executors.defaultThreadFactory(), new ThreadPoolExecutor.DiscardOldestPolicy()); try { for (int i = 0; i < 50; i++) { pool.execute(() -> { System.out.println(Thread.currentThread().getName() + "--->Pool Test"); }); } } catch (Exception e) { e.printStackTrace(); } finally { //线程池用完，程序结束，关闭线程池 pool.shutdown(); } } } 4种拒绝策略AbortPolicy() 线程池满了，还有人进来，不处理这个人的请求，同时抛出异常CallerRunsPolicy() 哪里来的请求，回到哪里去（请求对应的主方法）DiscardPolicy() 队列满了，丢掉后来的请求，不抛出异常DiscardOldestPolicy() 队列满了，尝试去和最早进行服务的窗口竞争，看那里的服务是否快要结束了，结束就进去提出请求，这种策略也不抛出异常小结1、线程池不允许使用Executor创建（不安全），而是通过ThreadPoolExecutor这样的方式2、如何定义线程池最大的大小？(1) CPU密集型根据cpu核数来设定Runtime.getRuntime().availableProcessors();(2) IO密集型判断程序中十分耗IO的线程，一般设置为其两倍的大小