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使用Executors 和 ThreadPoolExecutor实现Java线程池案例

首先需要一个工作线程：

package com.journaldev.threadpool;

public class WorkerThread implements Runnable {

private String command;

public WorkerThread(String s){

this.command=s;

}

@Override

public void run() {

System.out.println(Thread.currentThread().getName()+' Start. Command = '+command);

processCommand();

System.out.println(Thread.currentThread().getName()+' End.');

}

private void processCommand() {

try {

Thread.sleep(5000);

} catch (InterruptedException e) {

e.printStackTrace();

}

}

@Override

public String toString(){

return this.command;

}

}

下面是线程池的测试案例：

package com.journaldev.threadpool;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

public class SimpleThreadPool {

public static void main(String[] args) {

ExecutorService executor = Executors.newFixedThreadPool(5);

for (int i = 0; i < 10; i++) {

Runnable worker = new WorkerThread('' + i);

executor.execute(worker);

}

executor.shutdown();

while (!executor.isTerminated()) {

}

System.out.println('Finished all threads');

}

}

输出结果：

pool-1-thread-2 Start. Command = 1

pool-1-thread-4 Start. Command = 3

pool-1-thread-1 Start. Command = 0

pool-1-thread-3 Start. Command = 2

pool-1-thread-5 Start. Command = 4

pool-1-thread-4 End.

pool-1-thread-5 End.

pool-1-thread-1 End.

pool-1-thread-3 End.

pool-1-thread-3 Start. Command = 8

pool-1-thread-2 End.

pool-1-thread-2 Start. Command = 9

pool-1-thread-1 Start. Command = 7

pool-1-thread-5 Start. Command = 6

pool-1-thread-4 Start. Command = 5

pool-1-thread-2 End.

pool-1-thread-4 End.

pool-1-thread-3 End.

pool-1-thread-5 End.

pool-1-thread-1 End.

Finished all threads

线程池需要规定起初线程数目，使用RejectedExecutionHandler 实现：

package com.journaldev.threadpool;

import java.util.concurrent.RejectedExecutionHandler;

import java.util.concurrent.ThreadPoolExecutor;

public class RejectedExecutionHandlerImpl implements RejectedExecutionHandler {

@Override

public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {

System.out.println(r.toString() + ' is rejected');

}

}

通过监视线程池中结果：

package com.journaldev.threadpool;

import java.util.concurrent.ThreadPoolExecutor;

public class MyMonitorThread implements Runnable

{

private ThreadPoolExecutor executor;

private int seconds;

private boolean run=true;

public MyMonitorThread(ThreadPoolExecutor executor, int delay)

{

this.executor = executor;

this.seconds=delay;

}

public void shutdown(){

this.run=false;

}

@Override

public void run()

{

while(run){

System.out.println(

String.format('[monitor] [%d/%d] Active: %d, Completed: %d, Task: %d, isShutdown: %s, isTerminated: %s',

this.executor.getPoolSize(),

this.executor.getCorePoolSize(),

this.executor.getActiveCount(),

this.executor.getCompletedTaskCount(),

this.executor.getTaskCount(),

this.executor.isShutdown(),

this.executor.isTerminated()));

try {

Thread.sleep(seconds*1000);

} catch (InterruptedException e) {

e.printStackTrace();

}

}

}

}

下面是启动线程池实现：

package com.journaldev.threadpool;

import java.util.concurrent.ArrayBlockingQueue;

import java.util.concurrent.Executors;

import java.util.concurrent.ThreadFactory;

import java.util.concurrent.ThreadPoolExecutor;

import java.util.concurrent.TimeUnit;

public class WorkerPool {

public static void main(String args[]) throws InterruptedException{

//RejectedExecutionHandler implementation

RejectedExecutionHandlerImpl rejectionHandler = new RejectedExecutionHandlerImpl();

//Get the ThreadFactory implementation to use

ThreadFactory threadFactory = Executors.defaultThreadFactory();

//creating the ThreadPoolExecutor

ThreadPoolExecutor executorPool = new ThreadPoolExecutor(2, 4, 10, TimeUnit.SECONDS, new ArrayBlockingQueue(2), threadFactory, rejectionHandler);

//start the monitoring thread

MyMonitorThread monitor = new MyMonitorThread(executorPool, 3);

Thread monitorThread = new Thread(monitor);

monitorThread.start();

//submit work to the thread pool

for(int i=0; i<10; i++){

executorPool.execute(new WorkerThread('cmd'+i));

}

Thread.sleep(30000);

//shut down the pool

executorPool.shutdown();

//shut down the monitor thread

Thread.sleep(5000);

monitor.shutdown();

}

}

在初始化的ThreadPoolExecutor，我们保持初始池大小为2，最大池大小为4，工作队列大小为2。因此，如果有4个正在运行的任务，并提交了更多的任务，工作队列将持有其中2个和其余休息将他们交由RejectedExecutionHandlerImpl处理。

输出结果：

pool-1-thread-1 Start. Command = cmd0

pool-1-thread-4 Start. Command = cmd5

cmd6 is rejected

pool-1-thread-3 Start. Command = cmd4

pool-1-thread-2 Start. Command = cmd1

cmd7 is rejected

cmd8 is rejected

cmd9 is rejected

[monitor] [0/2] Active: 4, Completed: 0, Task: 6, isShutdown: false, isTerminated: false

[monitor] [4/2] Active: 4, Completed: 0, Task: 6, isShutdown: false, isTerminated: false

pool-1-thread-4 End.

pool-1-thread-1 End.

pool-1-thread-2 End.

pool-1-thread-3 End.

pool-1-thread-1 Start. Command = cmd3

pool-1-thread-4 Start. Command = cmd2

[monitor] [4/2] Active: 2, Completed: 4, Task: 6, isShutdown: false, isTerminated: false

[monitor] [4/2] Active: 2, Completed: 4, Task: 6, isShutdown: false, isTerminated: false

pool-1-thread-1 End.

pool-1-thread-4 End.

[monitor] [4/2] Active: 0, Completed: 6, Task: 6, isShutdown: false, isTerminated: false

[monitor] [2/2] Active: 0, Completed: 6, Task: 6, isShutdown: false, isTerminated: false

[monitor] [2/2] Active: 0, Completed: 6, Task: 6, isShutdown: false, isTerminated: false

[monitor] [2/2] Active: 0, Completed: 6, Task: 6, isShutdown: false, isTerminated: false

[monitor] [2/2] Active: 0, Completed: 6, Task: 6, isShutdown: false, isTerminated: false

[monitor] [2/2] Active: 0, Completed: 6, Task: 6, isShutdown: false, isTerminated: false

[monitor] [0/2] Active: 0, Completed: 6, Task: 6, isShutdown: true, isTerminated: true

[monitor] [0/2] Active: 0, Completed: 6, Task: 6, isShutdown: true, isTerminated: true