线程池（2）Executors.newFixedThreadPool

例子：

ExecutorService es = Executors.newFixedThreadPool(5);
        try {
            for (int i = 0; i < 20; i++) {
                Runnable syncRunnable = new Runnable() {
                    @Override
                    public void run() {
                        log.info(Thread.currentThread().getName());
                        try {
                            Thread.sleep(2000);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                };
                es.execute(syncRunnable);
            }
        } finally {
            es.shutdown();
        }

运行结果：
         *  10:20:14.630 pool-1-thread-5
            10:20:14.630 pool-1-thread-1
            10:20:14.632 pool-1-thread-4
            10:20:14.630 pool-1-thread-2
            10:20:14.630 pool-1-thread-3
            10:20:16.635 pool-1-thread-4
            10:20:16.635 pool-1-thread-5
            10:20:16.635 pool-1-thread-1
            10:20:16.636 pool-1-thread-2
            10:20:16.637 pool-1-thread-3
            10:20:18.637 pool-1-thread-3
            10:20:18.638 pool-1-thread-4
            10:20:18.641 pool-1-thread-5
            10:20:18.641 pool-1-thread-1
            10:20:18.642 pool-1-thread-2
            10:20:20.638 pool-1-thread-3
            10:20:20.639 pool-1-thread-4
            10:20:20.641 pool-1-thread-5
            10:20:20.642 pool-1-thread-1
            10:20:20.642 pool-1-thread-2

调用的ThreadPoolExecutor：

public static ExecutorService newFixedThreadPool(int nThreads) {
        return new ThreadPoolExecutor(nThreads, nThreads,
                                      0L, TimeUnit.MILLISECONDS,
                                      new LinkedBlockingQueue<Runnable>());
    }

corePoolSize=maximumPoolSize=5

keepAliveTime=0

allowCoreThreadTimeout=false（默认）

因此，

• 线程池中的线程数永远是5，永久存活。
• 对于新任务，当队列未满时，插入队列；当队列已满时，默认执行AbortPolicy，即抛出异常。
• 支持线程reuse