Question

java线程池ExecutorService，里面有多少空余线程，怎么看

Answer 1

ExecutorService是个接口，如果你是用Executors静态方法生产的实例，见具体实现。
比如：

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

那它是ThreadPoolExecutor的实例，你可以看它的方法，如getActiveCount()，getPoolSize()等。