Java 四种线程池的使用

通过Executors提供四中线程池，分别如下

newCachedThreadPool：创建一个可缓存线程池，若线程长度超过处理需要，可灵活回收空闲线程，若无可回收线程，则新建线程；

newFixedThreadPool：创建一个定长线程池，可控制线程最大并发数，超出的线程会在队列中等待；

newScheduledThreadPool：创建一个定长线程池，定时及支持周期执行任务；

newSingleThreadExecutor：创建一个单例化线程池，他会用唯一工作线程来执行任务，保证任务按照指定顺序（FIFO，LIFO优先级）来执行

1）newCachedThreadpool

　　线程池为无限大，当执行第二个任务时第一个已完成，会重复使用执行第一个任务的线程，而不用每次新建一个线程

import java.util.concurrent.ExecutorService;  
import java.util.concurrent.Executors;  
public class ThreadPoolExecutorTest {  
 public static void main(String[] args) {  
  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() {  
    public void run() {  
     System.out.println(index);  
    }  
   });  
  }  
 }  
} 

2）newFixedThreadPool

　　因为线程池大小为3，每个任务输出index后sleep2s，所以每2s打印3个数字

　　定长线程池的大小最好根据系统资源进行设置，如Runtime.getRuntime().availableProcessors()

import java.util.concurrent.ExecutorService;  
import java.util.concurrent.Executors;  
public class ThreadPoolExecutorTest {  
 public static void main(String[] args) {  
  ExecutorService fixedThreadPool = Executors.newFixedThreadPool(3);  
  for (int i = 0; i < 10; i++) {  
   final int index = i;  
   fixedThreadPool.execute(new Runnable() {  
    public void run() {  
     try {  
      System.out.println(index);  
      Thread.sleep(2000);  
     } catch (InterruptedException e) {  
      e.printStackTrace();  
     }  
    }  
   });  
  }  
 }  
}  

3）newScheduledThreadPool

　　延迟3s执行

package test;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
public class ThreadPoolExecutorTest {
 public static void main(String[] args) {
  ScheduledExecutorService scheduledThreadPool = Executors.newScheduledThreadPool(5);
  scheduledThreadPool.schedule(new Runnable() {
   public void run() {
    System.out.println("delay 3 seconds");
   }
  }, 3, TimeUnit.SECONDS);
 }
}

　　定期执行示例，---延迟1s后每3s执行一次

package test;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
public class ThreadPoolExecutorTest {
 public static void main(String[] args) {
  ScheduledExecutorService scheduledThreadPool = Executors.newScheduledThreadPool(5);
  scheduledThreadPool.scheduleAtFixedRate(new Runnable() {
   public void run() {
    System.out.println("delay 1 seconds, and excute every 3 seconds");
   }
  }, 1, 3, TimeUnit.SECONDS);
 }
}

4)newSingleThreadExecutor；

　　结果依次输出，相当于各执行各的任务，

package test;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class ThreadPoolExecutorTest {
 public static void main(String[] args) {
  ExecutorService singleThreadExecutor = Executors.newSingleThreadExecutor();
  for (int i = 0; i < 10; i++) {
   final int index = i;
   singleThreadExecutor.execute(new Runnable() {
    public void run() {
     try {
      System.out.println(index);
      Thread.sleep(2000);
     } catch (InterruptedException e) {
      e.printStackTrace();
     }
    }
   });
  }
 }
}