java中线程池创建的几种方式

java中创建线程池的方式一般有两种:通过Executors工厂方法创建通过new ThreadPoolExecutor(int corePoolSize,int 

java中创建线程池的方式一般有两种:

Executors工厂方法创建

package com.javaBase.LineDistancePond;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

/**
 * 〈一句话功能简述〉;
 * 〈功能详细描述〉
 *
 * @author jxx
 * @see [相关类/方法](可选)
 * @since [产品/模块版本] (可选)
 */
public class TestThreadPoolExecutor {

    public static void main(String[] args) {
        //创建使用单个线程的线程池
        ExecutorService es1 = Executors.newSingleThreadExecutor();
        for (int i = 0; i < 10; i++) {
            es1.submit(new Runnable() {
                @Override
                public void run() {
                    System.out.println(Thread.currentThread().getName() + "正在执行任务");
                }
            });
        }
        //创建使用固定线程数的线程池
        ExecutorService es2 = Executors.newFixedThreadPool(3);
        for (int i = 0; i < 10; i++) {
            es2.submit(new Runnable() {
                @Override
                public void run() {
                    System.out.println(Thread.currentThread().getName() + "正在执行任务");
                }
            });
        }
        //创建一个会根据需要创建新线程的线程池
        ExecutorService es3 = Executors.newCachedThreadPool();
        for (int i = 0; i < 20; i++) {
            es3.submit(new Runnable() {
                @Override
                public void run() {
                    System.out.println(Thread.currentThread().getName() + "正在执行任务");
                }
            });
        }
        //创建拥有固定线程数量的定时线程任务的线程池
        ScheduledExecutorService es4 = Executors.newScheduledThreadPool(2);
        System.out.println("时间:" + System.currentTimeMillis());
        for (int i = 0; i < 5; i++) {
            es4.schedule(new Runnable() {
                @Override
                public void run() {
                    System.out.println("时间:"+System.currentTimeMillis()+"--"+Thread.currentThread().getName() + "正在执行任务");
                }
            },3, TimeUnit.SECONDS);
        }
        //创建只有一个线程的定时线程任务的线程池
        ScheduledExecutorService es5 = Executors.newSingleThreadScheduledExecutor();
        System.out.println("时间:" + System.currentTimeMillis());
        for (int i = 0; i < 5; i++) {
            es5.schedule(new Runnable() {
                @Override
                public void run() {
                    System.out.println("时间:"+System.currentTimeMillis()+"--"+Thread.currentThread().getName() + "正在执行任务");
                }
            },3, TimeUnit.SECONDS);
        }
    }
}

只听到从山间传来架构君的声音:
雪声偏傍竹,寒梦不离家。有谁来对上联或下联?

new ThreadPoolExecutor()自定义创建

public ThreadPoolExecutor(int corePoolSize, int maximumPoolSize,long keepAliveTime,TimeUnit unit,BlockingQueue workQueue,ThreadFactory threadFactory,RejectedExecutionHandler handler) ;

corePoolSize:核心池的大小,这个参数跟后面讲述的线程池的实现原理有非常大的关系。在创建了线程池后,默认情况下,线程池中并没有任何线程,而是等待有任务到来才创建线程去执行任务,除非调用了prestartAllCoreThreads()或者prestartCoreThread()方法,从这2个方法的名字就可以看出,是预创建线程的意思,即在没有任务到来之前就创建corePoolSize个线程或者一个线程。默认情况下,在创建了线程池后,线程池中的线程数为0,当有任务来之后,就会创建一个线程去执行任务,当线程池中的线程数目达到corePoolSize后,就会把到达的任务放到缓存队列当中;
maximumPoolSize:线程池最大线程数,这个参数也是一个非常重要的参数,它表示在线程池中最多能创建多少个线程;
keepAliveTime:表示线程没有任务执行时最多保持多久时间会终止。默认情况下,只有当线程池中的线程数大于corePoolSize时,keepAliveTime才会起作用,直到线程池中的线程数不大于corePoolSize,即当线程池中的线程数大于corePoolSize时,如果一个线程空闲的时间达到keepAliveTime,则会终止,直到线程池中的线程数不超过corePoolSize。但是如果调用了allowCoreThreadTimeOut(boolean)方法,在线程池中的线程数不大于corePoolSize时,keepAliveTime参数也会起作用,直到线程池中的线程数为0;

unit:参数keepAliveTime的时间单位,有7种取值,在TimeUnit类中有7种静态属性:

此代码由Java架构师必看网-架构君整理
TimeUnit.DAYS; // TimeUnit.HOURS; //小时 TimeUnit.MINUTES; //分钟 TimeUnit.SECONDS; // TimeUnit.MILLISECONDS; //毫秒 TimeUnit.MICROSECONDS; //微妙 TimeUnit.NANOSECONDS; //纳秒

workQueue:一个阻塞队列,用来存储等待执行的任务,这个参数的选择也很重要,会对线程池的运行过程产生重大影响,一般来说,这里的阻塞队列有以下几种选择:

ArrayBlockingQueue
LinkedBlockingQueue
SynchronousQueue
PriorityBlockingQueue

ArrayBlockingQueue和PriorityBlockingQueue使用较少,一般使用LinkedBlockingQueue和SynchronousQueue。线程池的排队策略与BlockingQueue有关。

threadFactory:用于设置创建线程的工厂,可以通过线程工厂给每个创建出来的线程做些更有意义的事情,比如设置daemon和优先级等等
handler:表示当拒绝处理任务时的策略,有以下四种取值:

此代码由Java架构师必看网-架构君整理
1、AbortPolicy:直接抛出异常。 2、CallerRunsPolicy:只用调用者所在线程来运行任务。 3、DiscardOldestPolicy:丢弃队列里最近的一个任务,并执行当前任务。 4、DiscardPolicy:不处理,丢弃掉。 5、也可以根据应用场景需要来实现RejectedExecutionHandler接口自定义策略。如记录日志或持久化不能处理的任务。

ThreadPoolExecutor 源码理解

 public static void test(int size) {
        ThreadPoolExecutor poolExecutor = new ThreadPoolExecutor(5, 20, 2, TimeUnit.SECONDS, new LinkedBlockingQueue<>(5));

        for (int i = 0; i < size; i++) {
            poolExecutor.execute(new DemoTask(i));


            Console.log("poolSize:" + poolExecutor.getPoolSize());
            Console.log("corePoolSize:" + poolExecutor.getCorePoolSize());
            Console.log("maximumPoolSize:" + poolExecutor.getMaximumPoolSize());
            Console.log("queue:" + poolExecutor.getQueue().size());
            Console.log("completedTaskCount:" + poolExecutor.getCompletedTaskCount());
            Console.log("largestPoolSize:" + poolExecutor.getLargestPoolSize());
            Console.log("keepAliveTime:" + poolExecutor.getKeepAliveTime(TimeUnit.SECONDS));

        }

        poolExecutor.shutdown();
    }

class DemoTask implements Runnable {

    private int taskNum;

    public DemoTask(int taskNum) {
        this.taskNum = taskNum;
    }

    @Override
    public void run() {
        Console.log(StringUtils.center("正在执行" + taskNum, 20, "="));

        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        Console.log(StringUtils.center("执行完毕" + taskNum, 20, "="));
    }
}

 

执行结果:

=======正在执行0========
poolSize:1
corePoolSize:5
maximumPoolSize:20
queue:0
completedTaskCount:0
largestPoolSize:1
keepAliveTime:2
poolSize:2
corePoolSize:5
maximumPoolSize:20
queue:0
completedTaskCount:0
=======正在执行1========
largestPoolSize:2
keepAliveTime:2
poolSize:3
corePoolSize:5
maximumPoolSize:20
=======正在执行2========
queue:0
completedTaskCount:0
largestPoolSize:3
keepAliveTime:2
poolSize:4
corePoolSize:5
maximumPoolSize:20
queue:0
=======正在执行3========
completedTaskCount:0
largestPoolSize:4
keepAliveTime:2
poolSize:5
corePoolSize:5
=======正在执行4========
maximumPoolSize:20
queue:0
completedTaskCount:0
largestPoolSize:5
keepAliveTime:2
poolSize:5
corePoolSize:5
maximumPoolSize:20
queue:1
completedTaskCount:0
largestPoolSize:5
keepAliveTime:2
poolSize:5
corePoolSize:5
maximumPoolSize:20
queue:2
completedTaskCount:0
largestPoolSize:5
keepAliveTime:2
poolSize:5
corePoolSize:5
maximumPoolSize:20
queue:3
completedTaskCount:0
largestPoolSize:5
keepAliveTime:2
poolSize:5
corePoolSize:5
maximumPoolSize:20
queue:4
completedTaskCount:0
largestPoolSize:5
keepAliveTime:2
poolSize:5
corePoolSize:5
maximumPoolSize:20
queue:5
completedTaskCount:0
largestPoolSize:5
keepAliveTime:2
poolSize:6
corePoolSize:5
maximumPoolSize:20
queue:5
completedTaskCount:0
largestPoolSize:6
keepAliveTime:2
poolSize:7
corePoolSize:5
maximumPoolSize:20
queue:5
completedTaskCount:0
largestPoolSize:7
keepAliveTime:2
=======正在执行11=======
poolSize:8
corePoolSize:5
maximumPoolSize:20
queue:5
completedTaskCount:0
=======正在执行12=======
=======正在执行10=======
largestPoolSize:8
keepAliveTime:2
poolSize:9
corePoolSize:5
=======正在执行13=======
maximumPoolSize:20
queue:5
completedTaskCount:0
largestPoolSize:9
keepAliveTime:2
poolSize:10
corePoolSize:5
maximumPoolSize:20
=======正在执行14=======
queue:5
completedTaskCount:0
largestPoolSize:10
keepAliveTime:2
poolSize:11
corePoolSize:5
maximumPoolSize:20
queue:5
=======正在执行15=======
completedTaskCount:0
largestPoolSize:11
keepAliveTime:2
poolSize:12
corePoolSize:5
maximumPoolSize:20
queue:5
completedTaskCount:0
=======正在执行16=======
largestPoolSize:12
keepAliveTime:2
poolSize:13
corePoolSize:5
maximumPoolSize:20
=======正在执行17=======
queue:5
completedTaskCount:0
largestPoolSize:13
keepAliveTime:2
poolSize:14
corePoolSize:5
maximumPoolSize:20
queue:5
=======正在执行18=======
completedTaskCount:0
largestPoolSize:14
keepAliveTime:2
poolSize:15
corePoolSize:5
maximumPoolSize:20
=======正在执行19=======
queue:5
completedTaskCount:0
largestPoolSize:15
keepAliveTime:2
=======执行完毕0========
=======正在执行5========
=======执行完毕1========
=======执行完毕2========
=======正在执行6========
=======正在执行7========
=======执行完毕4========
=======正在执行8========
=======执行完毕3========
=======正在执行9========
=======执行完毕13=======
=======执行完毕12=======
=======执行完毕10=======
=======执行完毕11=======
=======执行完毕15=======
=======执行完毕16=======
=======执行完毕14=======
=======执行完毕19=======
=======执行完毕18=======
=======执行完毕17=======
=======执行完毕5========
=======执行完毕7========
=======执行完毕6========
=======执行完毕8========
=======执行完毕9========

 

 

参考链接:Java线程池(一)

       Java线程池(二)

架构君码字不易,如需转载,请注明出处:https://javajgs.com/archives/36375
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