线程池:先创建多个线程放在线程池中,当有任务需要执行时,从线程池中找一个空闲线程执行任务,任务完成后,并不销毁线程,而是返回线程池,等待新的任务安排。
线程池编程中,任务是提交给整个线程池的,并不是提交给某个具体的线程,而是由线程池从中挑选一个空闲线程来运行任务。一个线程同时只能执行一个任务,可以同时向一个线程池提交多个任务。
一、线程池创建方法:
a、创建一个拥有固定线程数的线程池
ExecutorService threadPool = Executors.newFixedThreadPool(3);
b、创建一个缓存线程池线程池中的线程数根据任务多少自动增删 动态变化
ExecutorService threadPool = Executors.newCacheThreadPool();
c、创建一个只有一个线程的线程池与单线程一样,但好处是保证池子里有一个线程,当线程意外死亡,会自动产生一个替补线程,始终有一个线程存活
ExecutorService threadPool = Executors.newSingleThreadExector();
二、往线程池中添加任务
threadPool.executor(Runnable)
三、关闭线程池:
threadPool.shutdown()线程全部空闲,没有任务就关闭线程池
threadPool.shutdownNow() 不管任务有没有做完,都关掉
演示代码如下:import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; public class ThreadPoolTest { public static void main(String[] args) { // ExecutorService threadPool=Executors.newFixedThreadPool(5);//创建一个可重用固定线程数的线程池,以共享的无界队列方式来运行这些线程。 // ExecutorService threadPool=Executors.newCachedThreadPool();//创建一个可根据需要创建新线程的线程池,但是在以前构造的线程可用时将重用它们。 ExecutorService threadPool=Executors.newSingleThreadExecutor();//创建一个使用单个 worker 线程的 Executor,以无界队列方式来运行该线程。 for(int i=1;i<=10;i++){ final int task=i; threadPool.execute(new Runnable() { @Override public void run() { for(int j=0;j<10;j++){ try { Thread.sleep(30); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println(Thread.currentThread().getName()+" is loop of "+j+" for task "+task); } } }); } System.out.println("all of tasks have committed!"); // threadPool.shutdown(); // threadPool.shutdownNow(); } }
运行结果为:
all of tasks have committed!
pool-1-thread-1 is loop of 0 for task 1
pool-1-thread-1 is loop of 1 for task 1
pool-1-thread-1 is loop of 2 for task 1
pool-1-thread-1 is loop of 3 for task 1
pool-1-thread-1 is loop of 4 for task 1
pool-1-thread-1 is loop of 5 for task 1
pool-1-thread-1 is loop of 6 for task 1
pool-1-thread-1 is loop of 7 for task 1
pool-1-thread-1 is loop of 8 for task 1
pool-1-thread-1 is loop of 9 for task 1
pool-1-thread-1 is loop of 0 for task 2
pool-1-thread-1 is loop of 1 for task 2
pool-1-thread-1 is loop of 2 for task 2
pool-1-thread-1 is loop of 3 for task 2
pool-1-thread-1 is loop of 4 for task 2
pool-1-thread-1 is loop of 5 for task 2
pool-1-thread-1 is loop of 6 for task 2
pool-1-thread-1 is loop of 7 for task 2
pool-1-thread-1 is loop of 8 for task 2
pool-1-thread-1 is loop of 9 for task 2
pool-1-thread-1 is loop of 0 for task 3
pool-1-thread-1 is loop of 1 for task 3
pool-1-thread-1 is loop of 2 for task 3
pool-1-thread-1 is loop of 3 for task 3
pool-1-thread-1 is loop of 4 for task 3
pool-1-thread-1 is loop of 5 for task 3
pool-1-thread-1 is loop of 6 for task 3
pool-1-thread-1 is loop of 7 for task 3
四、线程池启动定时器
a、创建调度线程池,提交任务 延迟指定时间后执行任务
Executors.newScheduledThreadPool(线程数).schedule(Runnable, 延迟时间,时间单位);
Executors.newScheduledThreadPool(3).schedule(new Runnable() { @Override public void run() { System.out.println("bombing!"); } }, 5, TimeUnit.SECONDS);
b、创建调度线程池,提交任务,延迟指定时间执行任务后,间隔指定时间循环执行
Executors.newScheduledThreadPool(线程数). scheduleAtFixedRate (Runnable, 延迟时间,间隔时间,时间单位);
Executors.newScheduledThreadPool(3).scheduleAtFixedRate(new Runnable() { @Override public void run() { System.out.println("bombing!"); } }, 5, 3, TimeUnit.SECONDS);
注:
所有的 schedule 方法都接受相对 延迟和周期作为参数,而不是绝对的时间或日期。将以 Date 所表示的绝对时间转换成要求的形式很容易。例如,要安排在某个以后的 Date 运行,可以使用:schedule(task, date.getTime() - System.currentTimeMillis(), TimeUnit.MILLISECONDS)。