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
大家好,我是架构君,一个会写代码吟诗的架构师。今天说一说java中线程池创建的几种方式,希望能够帮助大家进步!!!
java中创建线程池的方式一般有两种:
ThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime,
TimeUnit
unit,
BlockingQueue<Runnable> workQueue)自定义创建
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);
}
}
}
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; //天
TimeUnit.HOURS; //小时
TimeUnit.MINUTES; //分钟
TimeUnit.SECONDS; //秒
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。
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========
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参考链接:Java线程池(一)