java.util.concurrent.ThreadFactory 实例讲解

本文到实例中将讲解一下如何使用ThreadFactory接口。这个接口是Java自身提供的，用户可以实现它自定义自己的线程启动方式，可以设置线程名称、类型以及优先级等属性。

ThreadFactory vs Default ThreadFactory:
在一个典型的Java ExecutorService程序中，其线程都需要被指定以何种形式运行，如果程序初始化ExecutorService时没有指定ThreadFactory，程序会采用一个默认的ThreadFactory来生成提交线程，但是对于一个严谨对程序来说，定义自己的ThreadFactory永远是个最佳选择。Why？？

1. 设置更有描述意义的线程名称。如果使用默认的ThreadFactory，它给线程起名字大概规律就是pool-m-thread-n这个样子，如pool-1-thread-1。但是当你分析一个thread dump时，看着这样的名字就很难知道线程的目的。所以使用一个有描述意义的线程名称是分析追踪问题的clue NO.1。
2. 设置线程是否是守护线程，默认的ThreadFactory总是提交非守护线程
3. 设置线程优先级，默认ThreadFactory总是提交的一般优先级线程

例子:
CustomThreadFactoryBuilder类实现了一种优雅的Builder Mechanism方式去得到一个自定义ThreadFactory实例。ThreadFactory接口中有一个接受Runnable类型参数的方法newThread(Runnable r)，你自己的factory逻辑就应该写在这个方法中，去配置线程名称、优先级、守护线程状态等属性。

public class CustomThreadFactoryBuilder {

    private String namePrefix = null;
    private boolean daemon = false;
    private int priority = Thread.NORM_PRIORITY;

    public CustomThreadFactoryBuilder setNamePrefix(String namePrefix) {
        if (namePrefix == null) {
            throw new NullPointerException();
        }
        this.namePrefix = namePrefix;
        return this;
    }

    public CustomThreadFactoryBuilder setDaemon(boolean daemon) {
        this.daemon = daemon;
        return this;
    }

    public CustomThreadFactoryBuilder setPriority(int priority) {
        if (priority < Thread.MIN_PRIORITY){
            throw new IllegalArgumentException(String.format(
                    "Thread priority (%s) must be >= %s", priority, Thread.MIN_PRIORITY));
        }

        if (priority > Thread.MAX_PRIORITY) {
            throw new IllegalArgumentException(String.format(
                    "Thread priority (%s) must be <= %s", priority, Thread.MAX_PRIORITY));
        }

        this.priority = priority;
        return this;
    }

    public ThreadFactory build() {
        return build(this);
    }

    private static ThreadFactory build(CustomThreadFactoryBuilder builder) {
        final String namePrefix = builder.namePrefix;
        final Boolean daemon = builder.daemon;
        final Integer priority = builder.priority;
        final AtomicLong count = new AtomicLong(0);
         /*
        return new ThreadFactory() {
            @Override
            public Thread newThread(Runnable runnable) {
                Thread thread = new Thread(runnable);
                if (namePrefix != null) {
                    thread.setName(namePrefix + "-" + count.getAndIncrement());
                }
                if (daemon != null) {
                    thread.setDaemon(daemon);
                }
                if (priority != null) {
                    thread.setPriority(priority);
                }
                return thread;
            }
        };*/
        //jdk8中还是优先使用lamb表达式
        return (Runnable runnable) -> {
            Thread thread = new Thread(runnable);
            if (namePrefix != null) {
                thread.setName(namePrefix + "-" + count.getAndIncrement());
            }
            if (daemon != null) {
                thread.setDaemon(daemon);
            }
                /*
                    thread.setPriority(priority);
                */
            return thread;
        };
    }
}

SimpleTask类实现类Runnable接口，打印出了线程的运行属性（名称，优先级等）。

public class SimpleTask implements Runnable {
    private long sleepTime;

    public SimpleTask(long sleepTime) {
        super();
        this.sleepTime = sleepTime;
    }

    @Override
    public void run() {
        while (true) {
            try {
                System.out.println("Simple task is running on " 
                        + Thread.currentThread().getName() + " with priority " + Thread.currentThread().getPriority());
                Thread.sleep(sleepTime);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

CustomThreadFactoryDemo类使用我们上面的CustomThreadFactoryBuilder类创建类一个ThreadFactory实例，又使用这个实例获得类一个ExecutoryService，这样所有这个线程池中的线程都会按我们定义好的属性被生成，下面代码中执行类三个SimpleTask。

public class CustomThreadFactoryDemo {

    public static void main(String[] args) {

        ThreadFactory customThreadfactory = new CustomThreadFactoryBuilder()
        .setNamePrefix("DemoPool-Thread").setDaemon(false)
        .setPriority(Thread.MAX_PRIORITY).build();

        ExecutorService executorService = Executors.newFixedThreadPool(3,
        customThreadfactory);

        // Create three simple tasks with 1000 ms sleep time
        SimpleTask simpleTask1 = new SimpleTask(1000);
        SimpleTask simpleTask2 = new SimpleTask(1000);
        SimpleTask simpleTask3 = new SimpleTask(1000);

        // Execute three simple tasks with 1000 ms sleep time
        executorService.execute(simpleTask1);
        executorService.execute(simpleTask2);
        executorService.execute(simpleTask3);

    }

}

输出：

Simple task is running on DemoPool-Thread-0 with priority 10
Simple task is running on DemoPool-Thread-1 with priority 10
Simple task is running on DemoPool-Thread-2 with priority 10
Simple task is running on DemoPool-Thread-0 with priority 10
Simple task is running on DemoPool-Thread-1 with priority 10
Simple task is running on DemoPool-Thread-2 with priority 10
Simple task is running on DemoPool-Thread-0 with priority 10
Simple task is running on DemoPool-Thread-1 with priority 10
Simple task is running on DemoPool-Thread-2 with priority 10
Simple task is running on DemoPool-Thread-0 with priority 10
Simple task is running on DemoPool-Thread-1 with priority 10
Simple task is running on DemoPool-Thread-2 with priority 10