Java中Executors类中几种创建各类型线程池的方法及实例

青旅半醒 2022-06-02 04:42 212阅读 0赞

Executors：提供了一系列静态工厂方法用于创建各种线程池。

## 1.Executors.newCachedThreadPool创建可变线程池    ##

如果线程池长度超过处理需要，可灵活回收空闲线程，若无可回收，则新建线程。核心线程池大小为0，最大为Integer.MAX\_VALUE，线程空闲存活时间是60秒。

### 示例代码： ###

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");
            });
    }

### 执行结果： ###

![Center][]

### Executors内部创建newCachedThreadPool源码 ###

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

## 2.Executors.newFixedThreadPool创建固定大小线程池 ##

核心线程数即为最大线程数，线程不会被回收，直到调用shutdown方法回收

### 实例代码： ###

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

### 执行结果： ###

![Center 1][]

可以看到一直都是两个线程执行。

### Executors内部创建newFixedThreadPool源码 ###

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

## 3.Executors.newScheduledThreadPool创建定时或周期性任务执行线程池 ##

该线程池可用于定时或周期性任务的执行

### 定时实例代码： ###

ScheduledExecutorService scheduledThreadPool = Executors.newScheduledThreadPool(2);
        System.out.println(Thread.currentThread().getName() + "时间" + System.currentTimeMillis());
        //创建线程池后3秒执行
        scheduledThreadPool.schedule(() -> {
            System.out.println(Thread.currentThread().getName() + "时间" + System.currentTimeMillis());
            System.out.println("delay 3 seconds");
    }, 3, TimeUnit.SECONDS);

### 定时执行结果： ###

![Center 2][]

### 周期实例代码： ###

ScheduledExecutorService scheduleThreadPoolAtFixedRate = Executors.newScheduledThreadPool(5);
    System.out.println(Thread.currentThread().getName() + "时间" + System.currentTimeMillis());
    //创建线程池后1秒执行 ， 之后每3秒执行一次
    scheduleThreadPoolAtFixedRate.scheduleAtFixedRate(() -> {
          System.out.println(Thread.currentThread().getName() + "时间" + System.currentTimeMillis());
          System.out.println("delay 1 seconds, and excute every 3 seconds");
    }, 1, 3, TimeUnit.SECONDS);

### 周期执行结果： ###

![Center 3][]

### Executors内部创建newScheduledThreadPool源码 ###

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创建单线的线程池 ##

该线程池有且仅有一个线程执行任务，保证所有任务按照指定顺序(FIFO, LIFO, 优先级)执行。

### 实例代码： ###

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

### 运行结果： ###

![Center 4][]

### Executors内部创建newSingleThreadExecutor源码 ###

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

## 4.Executors.newWorkStealingPool创建并行执行线程池 ##

创建一个拥有多个任务队列（以便减少连接数）的线程池

### 实例代码： ###

// 设置并行级别为2，即默认每时每刻只有2个线程同时执行
            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);//此任务耗时1s
                        System.out.println("线程" + Thread.currentThread().getName() + "完成任务："
                                + count + "   时间为：" + System.currentTimeMillis());
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                });
            }

### 运行结果： ###

![Center 5][]

### Executors内部创建newWorkStealingPool源码 ###

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

[实例代码下载][Link 1]

[Center]: /images/20220602/5e8ce85a667945f084a7972bab1d6469.png
[Center 1]: /images/20220602/8b78ac4d8a1b4aa680b67b1b001d0ca9.png
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[Center 5]: /images/20220602/cd5f5421a8f34da6ac9ece11f78d85ad.png
[Link 1]: http://download.csdn.net/download/a491857321/10186817