3.2 线程复用：线程池

参数说明：public ThreadPoolExecutor(int corePoolSize,                          int maximumPoolSize,                          long keepAliveTime,                          TimeUnit unit,                          BlockingQueue<Runnable> workQueue) {    this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,         Executors.defaultThreadFactory(), defaultHandler);}

corePoolSize：指定了线程池中的数量。

maximumPoolSize：线程池中的最大线程数量。

keepAliveTime：当线程池超过corePoolSize数量的时候，多余的空闲线程的存活时间。即空闲线程在多长时间后销毁。

unit：时间单位。

workQueue：任务队列，被提交但尚未被执行的任务。

ThreadFactory:线程工厂，一般用改默认即可。

Handler：拒绝策略，当任务太多来不及处理，如何拒绝任务。

4种并发包下提供的线程池：

1.ExecutorService executorService = Executors.newSingleThreadExecutor();

public static ExecutorService newSingleThreadExecutor() {    return new FinalizableDelegatedExecutorService        (new ThreadPoolExecutor(1, 1,                                0L, TimeUnit.MILLISECONDS,                                new LinkedBlockingQueue<Runnable>()));}

2.ExecutorService executorService2 = Executors.newCachedThreadPool();

public static ExecutorService newCachedThreadPool() {    return new ThreadPoolExecutor(0, Integer.MAX_VALUE,                                  60L, TimeUnit.SECONDS,                                  new SynchronousQueue<Runnable>());}

3.ScheduledThreadPoolExecutor executorService3 = (ScheduledThreadPoolExecutor) Executors.newFixedThreadPool(1);

public static ExecutorService newFixedThreadPool(int nThreads) {    return new ThreadPoolExecutor(nThreads, nThreads,                                  0L, TimeUnit.MILLISECONDS,                                  new LinkedBlockingQueue<Runnable>());}

4.ScheduledExecutorService scheduledExecutorService = Executors.newScheduledThreadPool(1); 定时运行

public ScheduledThreadPoolExecutor(int corePoolSize) {    super(corePoolSize, Integer.MAX_VALUE, 0, TimeUnit.NANOSECONDS,          new DelayedWorkQueue());}

scheduleWithFixedDelay： 比如当前一个任务结束的时刻，开始结算间隔时间，如0秒开始执行第一次任务，任务耗时5秒，任务间隔时间3秒，那么第二次任务执行的时间是在第8秒开始。

scheduleAtFixedRate：没有什么歧义，很容易理解，就是每隔多少时间，固定执行任务。

scheduledExecutorService.scheduleAtFixedRate(new ThreadTest(), 1, 2, TimeUnit.SECONDS);

scheduledExecutorService.scheduleWithFixedDelay(new ThreadTest(), 1, 2, TimeUnit.SECONDS);

自定义线程池以及拒绝策略：

package 第三章.线程池;

import java.util.concurrent.*;

/** * Created by zzq on 2018/2/5. */public class 自定义线程池 {    public static void main(String[] args) {        ThreadPoolExecutor threadPoolExecutor=new ThreadPoolExecutor(2,                5,                0,                TimeUnit.SECONDS,                new ArrayBlockingQueue<Runnable>(2),                Executors.defaultThreadFactory(),//                new ThreadPoolExecutor.AbortPolicy());//第一种拒绝策略：直接抛出异常AbortPolicy//                new ThreadPoolExecutor.CallerRunsPolicy());//第二种拒绝策略：新建一个线程//                new ThreadPoolExecutor.DiscardOldestPolicy());//第三种拒绝策略：在队列里推出一个最早的//                new ThreadPoolExecutor.DiscardPolicy());//第四种：直接丢弃。                new RejectedExecutionHandler() {                    public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {                        System.out.println(Thread.currentThread().getName()+"被抛弃了");                        try {                            Thread.sleep(2000);                        } catch (InterruptedException e) {                            e.printStackTrace();                        }                        System.out.println(Thread.currentThread().getName()+"拒绝成功");

}                });//自定义拒绝策略        for (int i = 0; i < 10; i++) {            final int finalI = i;            threadPoolExecutor.execute(new Runnable() {                public void run() {                    System.out.println(Thread.currentThread().getName()+"开始"+ finalI);                    try {                        Thread.sleep(10000);                    } catch (InterruptedException e) {                        e.printStackTrace();                    }                    System.out.println(Thread.currentThread().getName()+"结束"+ finalI);                }            });        }

}

}

自定义线程创建：

package 第三章.线程池;

import java.util.concurrent.*;

/** * Created by zzq on 2018/2/5. */public class 自定义线程创建 {    public static void main(String[] args) {        ThreadPoolExecutor threadPoolExecutor=new ThreadPoolExecutor(2,                5,                0,                TimeUnit.SECONDS,                new ArrayBlockingQueue<Runnable>(2),                new ThreadFactory() {                    public Thread newThread(Runnable r) {                        Thread t=new Thread(r);                        System.out.println("Creat");                        return t;                    }                },//                new ThreadPoolExecutor.AbortPolicy());//第一种拒绝策略：直接抛出异常AbortPolicy                new ThreadPoolExecutor.CallerRunsPolicy());//第二种拒绝策略：新建一个线程//                new ThreadPoolExecutor.DiscardOldestPolicy());//第三种拒绝策略：在队列里推出一个最早的//                new ThreadPoolExecutor.DiscardPolicy());//第四种：直接丢弃。//                new RejectedExecutionHandler() {//                    public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {//                        System.out.println(Thread.currentThread().getName() + "被抛弃了");//                        try {//                            Thread.sleep(2000);//                        } catch (InterruptedException e) {//                            e.printStackTrace();//                        }//                        System.out.println(Thread.currentThread().getName() + "拒绝成功");////                    }//                });//自定义拒绝策略。        for (int i = 0; i < 10; i++) {            final int finalI = i;            threadPoolExecutor.execute(new Runnable() {                public void run() {                    System.out.println(Thread.currentThread().getName()+"开始"+ finalI);                    try {                        Thread.sleep(10000);                    } catch (InterruptedException e) {                        e.printStackTrace();                    }                    System.out.println(Thread.currentThread().getName()+"结束"+ finalI);                }            });        }    }}

原文地址：https://www.cnblogs.com/anxbb/p/8425672.html