线程池的作用:
提供系统效率;如果每个请求到达就创建一个线程,开销是相当大的,服务器创建和销毁线程花费的时间和系统资源都相当大;如果线程数量太多,线程之间的切换也会消耗大量时间和资源。通过对多个任务重复使用线程,那么线程创建和销毁的开销就分摊到了多个任务上,平均每个任务所花费的时间和资源就少了很多。
1、 newCachedThreadPool
创建可缓存线程池,如果线程池的大小超过处理需要的大小,可灵活回收空闲线程,如果不能回收,就创建线程,回收的线程可以用作执行新的任务
import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; public class CachedThreadPool { @Override public void run() { ExecutorService cachedThreadPool = Executors.newCachedThreadPool(); for(int i = 0; i < 10; i++) { final int index = i; try { Thread.sleep(index * 1000); } catch (InterruptedException e) { e.printStackTrace(); } cachedThreadPool.execute(new Runnable() { @Override public void run() { System.out.println(index); } }); } } }
2、 newFixedThreadPool
创建定长线程,可控制线程的最大并发数,超出的线程需在队列中等待
import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; public class FixedThreadPool { @Override public void run() { ExecutorService fixedThreadPool = Executors.newFixedThreadPool(3); for (int i = 0; i < 10; i++) { final int index = i; fixedThreadPool.execute(new Runnable() { @Override public void run() { try { System.out.println(index); Thread.sleep(2000); } catch (InterruptedException e) { e.printStackTrace(); } } }); } } }
3、 newScheduledThreadPool
创建定长线程,支持按照设定的时间延迟执行或者周期性执行
import java.util.concurrent.Executors; import java.util.concurrent.ScheduledExecutorService; import java.util.concurrent.TimeUnit; public class ScheduledThreadPool { @Override public void run() { ScheduledExecutorService scheduledThreadPool = Executors.newScheduledThreadPool(3); scheduledThreadPool.scheduleAtFixedRate(new Runnable() { @Override public void run() { System.out.println("3 seconds delay"); } }, 1, 3, TimeUnit.SECONDS); } }
4、 newSingleThreadPool
单线程化的线程池,所有的任务的执行顺序按照指定的顺序执行(FIFO、LIFO、优先级等)
import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; public class SingleThreadPool { @Override public void run() { ExecutorService singleThreadPool = Executors.newSingleThreadExecutor(); for (int i = 0 ; i < 10; i++) { final int index = i; singleThreadPool.execute(new Runnable() { @Override public void run() { try { System.out.println(index); Thread.sleep(2000); } catch (InterruptedException e) { e.printStackTrace(); } } }); } } }