//对于每个任务，如果有空闲的线程可用，立即让他执行任务，//没有空闲的线程则创建一个线程。ExecutorService pool = Executors.newCachedThreadPool();//固定大小的线程池，任务数 > 空闲线程数，得不到服务的任务置于队列ExecutorService pool = Executors.newFixedThreadPool;//退化的大小为1的线程池，由一个线程逐个执行提交的任务。ExecutorService pool = Executors.newSingleThreadPool();

    //返回的对象可以调用isDone(),cancel(),isCancelledFuture<?> submit(Runnable task);//get() 返回指定的result对象Future<T> submit(Runnable task,T result);//返回的对象将在计算结果准备好的时候得到它。Future<T> submit(Callable<T> task);

   /** 线程任务:计算目录中所有包含给定关键字的文件的数量。*/class MatchCounter implements Callable<Integer>{private File directory;private String keyword;private ExecutorService pool;private int count;/*** Constructs a MatchCounter.* @param directory 给定的目录* @param keyword 关键字* @param pool 用来执行任务的线程池*/public MatchCounter(File directory, String keyword, ExecutorService pool){this.directory = directory;this.keyword = keyword;this.pool = pool;}@Overridepublic Integer call(){count = 0;try{File[] files = directory.listFiles();//线程执行结果集合List<Future<Integer>> results = new ArrayList<>();for (File file : files)//遍历给定目录中的所有文件//如果是文件夹if (file.isDirectory()){//递归MatchCounter counter = new MatchCounter(file, keyword, pool);Future<Integer> result = pool.submit(counter);results.add(result);}//如果是文件，则调用search()方法 看是否包含关键字。else{if (search(file)) count++;}for (Future<Integer> result : results)try{int a = result.get();count += result.get();}catch (ExecutionException e){e.printStackTrace();}}catch (InterruptedException e){}return count;}/*** Searches a file for a given keyword.* @param file the file to search* @return true if the keyword is contained in the file*/public boolean search(File file){try{try (Scanner in = new Scanner(file, "UTF-8")){boolean found = false;while (!found && in.hasNextLine()){String line = in.nextLine();if (line.contains(keyword)) found = true;}return found;}}catch (IOException e){return false;}}}

    public class ThreadPoolTest{public static void main(String[] args) throws Exception{try (Scanner in = new Scanner(System.in)){System.out.print("请输入要查找的目录：");String directory = in.nextLine();System.out.print("请输入要查找的关键字：");String keyword = in.nextLine();ExecutorService pool = Executors.newCachedThreadPool();MatchCounter counter = new MatchCounter(new File(directory), keyword, pool);Future<Integer> result = pool.submit(counter);try{System.out.println(result.get() + " 匹配的文件");}catch (ExecutionException e){e.printStackTrace();}catch (InterruptedException e){}pool.shutdown();int largestPoolSize = ((ThreadPoolExecutor) pool).getLargestPoolSize();System.out.println("线程池最大数量 =" + largestPoolSize);}}}