1 线程池

• 提供了一个线程队列，队列中保存着所有等待状态的线程。避免了创建与销毁的额外开销，提高了响应速度

2 线程池的体系结构

3 工具类：Excutors

• 更方便的工厂方法获取可用线程

方法名	方法解释
newFixedThreadPool(int 线程数)	创建固定大小的线程池
newCachedThreadPool()	缓存线程池，线程池的数量不固定，可以根据需求自动的更改数量
newSingleThreadExecutor()	创建单个线程池，线程池中只有一个线程
newScheduledThreadPool()	创建固定大小的线程，可以延迟或定时的执行任务

• 使用步骤
  • 创建线程池
  • 注入任务
  • 关闭线程

package JUC;import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;public class TestThreadPools {public static void main(String[] args) {test02();}public static void test01() {// 创建固定大小的线程池ExecutorService threadPool = Executors.newFixedThreadPool(5);ThreadDemo6 demo = new ThreadDemo6();for (int i = 0; i < 10; i++) {// 注入任务threadPool.submit(demo);}// 等待线程的任务结束后关闭该线程threadPool.shutdown();// 没有条件的直接关闭线程，不推荐使用// threadPool.shutdownNow();}public static void test02() {ExecutorService threadPool = Executors.newFixedThreadPool(5);Future<Integer> future = threadPool.submit(new Callable<Integer>() {@Overridepublic Integer call() throws Exception {int sum = 0;for (int i = 0; i < 100; i++) {sum += i;}return sum;}});try {System.out.println(future.get());} catch (Exception e) {e.printStackTrace();}threadPool.shutdown();}
}class ThreadDemo6 implements Runnable {private int i = 0;@Overridepublic void run() {for (int i = 0; i < 100; i++) {System.out.println(Thread.currentThread().getName() + " i = " + i);}}
}

4 线程调度

• schedule()方法的参数
  • 参数一：Callable的任务
  • 参数二：多长时间执行一次（int型）
  • 参数三：TimeUnit的时间单位（SECONDS等）

package JUC;import java.util.Random;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;public class ScheduledThreadPoolTest {public static void main(String[] args) throws InterruptedException, ExecutionException {ScheduledExecutorService threadPool = Executors.newScheduledThreadPool(5);for (int i = 0; i < 5; i++) {Future future = threadPool.schedule(new Callable<Integer>() {@Overridepublic Integer call() throws Exception {int num = new Random().nextInt(100);System.out.print(Thread.currentThread().getName() + " : ");return num;}}, 1, TimeUnit.SECONDS);System.out.println(future.get());}threadPool.shutdown();}
}