java并发编程——线程池ThreadPoolExecutor使用

线程池ThreadPoolExecutor使用

线程池ThreadPoolExecutor使用

以下代码基于JDK1.8。

package thread;

import java.util.concurrent.*;

/**
 * 第四种使用Java多线程的方式，线程池
 */
public class MyThreadPoolDemo {
    public static void main(String[] args) {
        System.out.println("Fixed Thread Pool");
        fixedThreadPool();
        System.out.println("Single Thread Pool");
        singleThreadPool();
        System.out.println("Cached Thread Pool");
        cachedThreadPool();
        System.out.println("Custom Thread Pool");//自定义的线程池
        customThreadPool();
    }

    private static void customThreadPool() {
        ExecutorService threadPool=
                new ThreadPoolExecutor(2,
                        5,
                        1L,
                        TimeUnit.SECONDS,
                        new LinkedBlockingQueue<>(3),
                        Executors.defaultThreadFactory(),
                        new ThreadPoolExecutor.AbortPolicy()
                );
        try {
            for (int i = 0; i < 9; i++) {
                threadPool.execute(() -> {
                    System.out.println(Thread.currentThread().getName()+"\t办理业务");
                });
            }

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            threadPool.shutdown();
        }
    }

    private static void cachedThreadPool() {
        //不定量线程
        ExecutorService threadPool = Executors.newCachedThreadPool();
        try {
            for (int i = 0; i < 9; i++) {
                threadPool.execute(() -> {
                    System.out.println(Thread.currentThread().getName()+"\t办理业务");
                });
            }

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            threadPool.shutdown();
        }
    }

    private static void singleThreadPool() {
        //一池1个线程
        ExecutorService threadPool = Executors.newSingleThreadExecutor();
        try {
            for (int i = 0; i < 9; i++) {
                threadPool.execute(() -> {
                    System.out.println(Thread.currentThread().getName() + "\t办理业务");
                });
            }

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            threadPool.shutdown();
        }
    }

    private static void fixedThreadPool() {
        //一池5个线程
        ExecutorService threadPool = Executors.newFixedThreadPool(5);
        //一般常用try-catch-finally
        //模拟10个用户来办理业务，每个用户就是一个线程
        try {
            for (int i = 0; i < 9; i++) {
                threadPool.execute(() -> {
                    System.out.println(Thread.currentThread().getName() + "\t办理业务");
                });
            }

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            threadPool.shutdown();
        }
    }
}

测试

    public static void main(String[] args) {
        System.out.println("Custom Thread Pool");
        customThreadPool();
    }

    private static void customThreadPool() {
        ExecutorService threadPool=
                new ThreadPoolExecutor(2,
                        5,
                        1L,
                        TimeUnit.SECONDS,
                        new LinkedBlockingQueue<>(3),
                        Executors.defaultThreadFactory(),
                        new ThreadPoolExecutor.AbortPolicy()
                );
        try {
            for (int i = 0; i < 9; i++) {
                threadPool.execute(() -> {
                    System.out.println(Thread.currentThread().getName()+"\t办理业务");
                });
            }

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            threadPool.shutdown();
        }
    }

运行

Custom Thread Pool
pool-1-thread-2	办理业务
pool-1-thread-1	办理业务
pool-1-thread-2	办理业务
pool-1-thread-2	办理业务
pool-1-thread-1	办理业务
pool-1-thread-3	办理业务
pool-1-thread-4	办理业务
pool-1-thread-2	办理业务
pool-1-thread-5	办理业务

当模拟15个用户来办理业务，每个用户就是一个来自外部的请求线程

            //模拟15个用户来办理业务，每个用户就是一个来自外部的请求线程
            for (int i = 0; i < 15; i++) {
                threadPool.execute(() -> {
                    System.out.println(Thread.currentThread().getName()+"\t办理业务");
                });
            }

这时抛出了rejectedExecution异常。

如果没有抛出异常，多试几次。

为什么要用自定义线程池