线程池中的线程工厂

既然都使用的线程池，则创建线程的工作都交付给了线程池去完成。我们只需要告诉线程池需要多少个线程，剩下的工作都交于线程池完成。在线程池中创建线程使用的是线程工厂，
下面我们看看有哪些线程工厂：

ThreadFactory(父级接口)

public interface ThreadFactory {
    

    // 构造一个新的Thread 。实现还可以初始化优先级、名称、守护进程状态、 ThreadGroup等
    Thread newThread(Runnable r);
}

DefaultThreadFactory(默认使用)

// 默认线程工厂
static class DefaultThreadFactory implements ThreadFactory {
    
       // 线程池号
        private static final AtomicInteger poolNumber = new AtomicInteger(1);
        // 线程组
        private final ThreadGroup group;
        // 线程号
        private final AtomicInteger threadNumber = new AtomicInteger(1);
        // 线程名称前缀
        private final String namePrefix;
        
        DefaultThreadFactory() {
    
            SecurityManager s = System.getSecurityManager();
            // 获取线程组
            group = (s != null) ? s.getThreadGroup() :
                                  Thread.currentThread().getThreadGroup();
            // 线程名称前缀 = pool + 线程池号 + thread 
            namePrefix = "pool-" +
                          poolNumber.getAndIncrement() +
                         "-thread-";
        }
 
        // 创建新的线程
        public Thread newThread(Runnable r) {
    
            // 创建线程(线程组，任务，线程名称)
            Thread t = new Thread(group, r,
                                  namePrefix + threadNumber.getAndIncrement(),
                                  0);
            // 判断当前查询是否是守护线程
            // 如果是守护线程则设置为非守护线程 
            if (t.isDaemon())
                t.setDaemon(false);
            // 判断线程的优先级是否为默认优先级 
            if (t.getPriority() != Thread.NORM_PRIORITY)
                // 将线程优先级设置为默认优先级
                t.setPriority(Thread.NORM_PRIORITY);
            return t;
        }
    }

PrivilegedThreadFactory

// 特权线程工厂
// 线程工厂捕获访问控制上下文和类加载器
static class PrivilegedThreadFactory extends DefaultThreadFactory {
    
        private final AccessControlContext acc;
        private final ClassLoader ccl;

        PrivilegedThreadFactory() {
    
            super();
            SecurityManager sm = System.getSecurityManager();
            if (sm != null) {
    
                // Calls to getContextClassLoader from this class
                // never trigger a security check, but we check
                // whether our callers have this permission anyways.
                sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);

                // Fail fast
                sm.checkPermission(new RuntimePermission("setContextClassLoader"));
            }
            this.acc = AccessController.getContext();
            this.ccl = Thread.currentThread().getContextClassLoader();
        }

        public Thread newThread(final Runnable r) {
    
            return super.newThread(new Runnable() {
    
                public void run() {
    
                    AccessController.doPrivileged(new PrivilegedAction<Void>() {
    
                        public Void run() {
    
                            Thread.currentThread().setContextClassLoader(ccl);
                            r.run();
                            return null;
                        }
                    }, acc);
                }
            });
        }
    }