java线程池的使用

JDK 里面自带了线程池的实现,相比较于我们自己编写线程类,线程池可以更好地管理线程资源.

简介

下面的图是和线程池相关的几个类之间的关系

Executors类是JDK提供的线程池工具类,里面有几个实现线程池的默认方法,可以直接调用.

• Executors.newCachedThreadPool（*线程池，自动线程回收）
• Executors.newFixedThreadPool（固定大小的线程池）；
• Executors.newSingleThreadExecutor（单一后台线程）；
• 这三个方法的底层都是调用的 ThreadPoolExecutor 类的构造器实现的,所以我们也可以自己来控制线程池的各种参数,推荐自己实现.

测试代码

1.使用 Executors 工厂类来建立线程池

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

public class ThreadPoolDemo3 {

    public static void main(String[] args) {
        ExecutorService executorService = Executors.newFixedThreadPool(5);
        for (int i = 0; i < 5; i++) {
            int index = i;
            executorService.execute(() -> divTask(100, index));
        }
        executorService.shutdown();
    }

    private static void divTask(int a, int b) {
        try {
            double result = a / b;
            System.out.println(result);
        } catch (ArithmeticException e) {
            e.printStackTrace();
            System.out.println("除数不能为0!");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

打印结果:
33.0
100.0
50.0
25.0
除数不能为0!
java.lang.ArithmeticException: / by zero
	at com.example.springboot01.util.ThreadPoolDemo3.divTask(ThreadPoolDemo3.java:19)
	at com.example.springboot01.util.ThreadPoolDemo3.lambda$main$0(ThreadPoolDemo3.java:12)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)

2.使用 ThreadPoolExecutor 类定义线程池

import java.util.concurrent.*;

public class ThreadPoolDemo3 {

    public static void main(String[] args) {
        ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(1, 2,
                1000, TimeUnit.MILLISECONDS, new SynchronousQueue<Runnable>(),
                Executors.defaultThreadFactory(), new ThreadPoolExecutor.CallerRunsPolicy());

        for (int i = 0; i < 5; i++) {
            int index = i;
            threadPoolExecutor.execute(() -> divTask(100, index));
        }
        threadPoolExecutor.shutdown();
    }

    private static void divTask(int a, int b) {
        try {
            double result = a / b;
            System.out.println(result);
        } catch (ArithmeticException e) {
            e.printStackTrace();
            System.out.println("除数不能为0!");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

打印结果:
50.0
33.0
25.0
除数不能为0!
100.0
java.lang.ArithmeticException: / by zero
	at com.example.springboot01.util.ThreadPoolDemo3.divTask(ThreadPoolDemo3.java:23)
	at com.example.springboot01.util.ThreadPoolDemo3.lambda$main$0(ThreadPoolDemo3.java:16)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)

ThreadPoolExecutor 类构造器各参数说明

public ThreadPoolExecutor(
	int corePoolSize,
	int maximumPoolSize,
    long keepAliveTime,
    TimeUnit unit,
    BlockingQueue<Runnable> workQueue,
    ThreadFactory threadFactory,
    RejectedExecutionHandler handler){}

序号	名称	类型	含义
1	corePoolSize	int	核心线程池大小
2	maximumPoolSize	int	最大线程池大小
3	keepAliveTime	long	线程最大空闲时间
4	unit	TimeUnit	时间单位
5	workQueue	BlockingQueue	线程等待队列
6	threadFactory	ThreadFactory	线程创建工厂
7	handler	RejectedExecutionHandler	拒绝策略

参考资料

线程池之ThreadPoolExecutor概述
线程池之ThreadPoolExecutor使用