Executors：提供了一系列靜態工廠方法用於建立各種執行緒池。

1.Executors.newCachedThreadPool建立可變執行緒池

如果執行緒池長度超過處理需要，可靈活回收空閒執行緒，若無可回收，則新建執行緒。核心執行緒池大小為0，最大為Integer.MAX_VALUE，執行緒空閒存活時間是60秒。

示例程式碼：

ExecutorService cachedThreadPool = Executors.newCachedThreadPool();
        for (int i = 1; i <= 5; i++) {
            final int index = i;
            cachedThreadPool.execute(() -> {
                System.out.println(index + "start");
                System.out.println(Thread.currentThread().getName());
                try {
                    Thread.sleep(index * 1500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(index + "end");
        });
}
 

執行結果：

Executors內部建立newCachedThreadPool原始碼

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

2.Executors.newFixedThreadPool建立固定大小執行緒池

例項程式碼：

ExecutorService fixedThreadPool = Executors.newFixedThreadPool(2);
	for (int i = 1; i <= 4; i++) {
            final int index = i;
            System.out.println(Thread.currentThread().getName() + "時間" + System.currentTimeMillis());
            fixedThreadPool.execute(() -> {
                try {
                    System.out.println(Thread.currentThread().getName() + "時間" + System.currentTimeMillis());
                    Thread.sleep(1500);
                    System.out.println(Thread.currentThread().getName() + "end");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
        });
 }
 

執行結果：

Executors內部建立newFixedThreadPool原始碼

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

3.Executors.newScheduledThreadPool建立定時或週期性任務執行執行緒池

定時例項程式碼：

ScheduledExecutorService scheduledThreadPool = Executors.newScheduledThreadPool(2);
    System.out.println(Thread.currentThread().getName() + "時間" + System.currentTimeMillis());
    //建立執行緒池後3秒執行
    scheduledThreadPool.schedule(() -> {
        System.out.println(Thread.currentThread().getName() + "時間" + System.currentTimeMillis());
        System.out.println("delay 3 seconds");
}, 3, TimeUnit.SECONDS);

定時執行結果：

週期例項程式碼：

ScheduledExecutorService scheduleThreadPoolAtFixedRate = Executors.newScheduledThreadPool(5);
System.out.println(Thread.currentThread().getName() + "時間" + System.currentTimeMillis());
//建立執行緒池後1秒執行 ， 之後每3秒執行一次
scheduleThreadPoolAtFixedRate.scheduleAtFixedRate(() -> {
      System.out.println(Thread.currentThread().getName() + "時間" + System.currentTimeMillis());
      System.out.println("delay 1 seconds, and excute every 3 seconds");
}, 1, 3, TimeUnit.SECONDS);

週期執行結果：

Executors內部建立newScheduledThreadPool原始碼

 public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize) {
        return new ScheduledThreadPoolExecutor(corePoolSize);
 }

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

4.Executors.singleThreadExecutor建立單線的執行緒池

例項程式碼：

ExecutorService singleThreadExecutor = Executors.newSingleThreadExecutor();
	for (int i = 1; i <= 4; i++) {
            final int index = i;
            System.out.println(Thread.currentThread().getName() + "時間" + System.currentTimeMillis());
            singleThreadExecutor.execute(() -> {
                try {
                    System.out.println(Thread.currentThread().getName() + "時間" + System.currentTimeMillis());
                    Thread.sleep(1500);
                    System.out.println(Thread.currentThread().getName() + "end");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
        });
}

執行結果：

Executors內部建立newSingleThreadExecutor原始碼

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

4.Executors.newWorkStealingPool建立並行執行執行緒池

例項程式碼：

// 設定並行級別為2，即預設每時每刻只有2個執行緒同時執行
        ExecutorService newWorkStealingPool = Executors.newWorkStealingPool(2);

        for (int i = 1; i <= 4; i++) {
            final int count = i;
            System.out.println("execute" + i);
            newWorkStealingPool.execute(() -> {
                try {
                    Thread.sleep(1000);//此任務耗時1s
                    System.out.println("執行緒" + Thread.currentThread().getName() + "完成任務："
                            + count + "   時間為：" + System.currentTimeMillis());
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            });
        }

執行結果：

Executors內部建立newWorkStealingPool原始碼

public static ExecutorService newWorkStealingPool(int parallelism) {
        return new ForkJoinPool
            (parallelism,
             ForkJoinPool.defaultForkJoinWorkerThreadFactory,
             null, true);
    }