线程池-参数篇：3.ThreadFactory

接口定义

public interface ThreadFactory {

    /**
     * Constructs a new {@code Thread}.  Implementations may also initialize
     * priority, name, daemon status, {@code ThreadGroup}, etc.
     *
     * @param r a runnable to be executed by new thread instance
     * @return constructed thread, or {@code null} if the request to
     *         create a thread is rejected
     */
    Thread newThread(Runnable r);
}

从注释中可知，通过ThreadFactory的newThread方法，可以对创建的线程做一些操控：

• 指定优先级
• 指定线程名称，方便监控
• 指定是否守护线程，守护线程不阻塞进程
• 指定线程组

默认的ThreadFactory

 /**
     * The default thread factory
     */
    static class DefaultThreadFactory implements ThreadFactory {
        private static final AtomicInteger poolNumber = new AtomicInteger(1);
        private final ThreadGroup group;
        private final AtomicInteger threadNumber = new AtomicInteger(1);
        private final String namePrefix;

        DefaultThreadFactory() {
            SecurityManager s = System.getSecurityManager();
            group = (s != null) ? s.getThreadGroup() :
                                  Thread.currentThread().getThreadGroup();
            namePrefix = "pool-" +
                          poolNumber.getAndIncrement() +
                         "-thread-";
        }

        public Thread newThread(Runnable r) {
            Thread t = new Thread(group, r,
                                  namePrefix + threadNumber.getAndIncrement(),
                                  0);
            if (t.isDaemon())
                t.setDaemon(false);
            if (t.getPriority() != Thread.NORM_PRIORITY)
                t.setPriority(Thread.NORM_PRIORITY);
            return t;
        }
    }

默认线程池所创建的线程有一些特征：

• 名字有规律，形如 pool-N-thread-M (N:表示第几个线程池；M表示线程池内的第几个线程）
• 非守护线程，会阻塞进程退出，需要显式的关闭线程池
• 线程的优先级为：NORM_PRIORITY

自定义ThreadFactory

• 根据自己的需求，指定线程是否守护线程
• 定义识别度更高的线程名称
• 根据需要设置线程的优先级