1. 創建線程池的方法之三：
//對于每個任務，如果有空閑的線程可用，立即讓他執行任務，//沒有空閑的線程則創建一個線程。ExecutorService pool = Executors.newCachedThreadPool();//固定大小的線程池，任務數 > 空閑線程數，得不到服務的任務置于隊列ExecutorService pool = Executors.newFixedThreadPool;//退化的大小為1的線程池，由一個線程逐個執行提交的任務。ExecutorService pool = Executors.newSingleThreadPool();
java中能用多個線程池嗎、2. 把任務交給線程池：
//返回的對象可以調用isDone(),cancel(),isCancelledFuture<?> submit(Runnable task);//get() 返回指定的result對象Future<T> submit(Runnable task,T result);//返回的對象將在計算結果準備好的時候得到它。Future<T> submit(Callable<T> task);
3.用完一個線程池的時候，調用shutdown() 啟動線程池的關閉序列。被關閉的執行器不再接受新的任務，當任務都結束后，線程池中的線程死亡。
4. 案例：給定一個目錄，查找目錄中文本文檔內容包含指定關鍵字的文檔的數量。
條件：目錄、關鍵字
4.1 任務類（線程類）
/** 線程任務:計算目錄中所有包含給定關鍵字的文件的數量。*/class MatchCounter implements Callable<Integer>{private File directory;private String keyword;private ExecutorService pool;private int count;/*** Constructs a MatchCounter.* @param directory 給定的目錄* @param keyword 關鍵字* @param pool 用來執行任務的線程池*/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();//線程執行結果集合List<Future<Integer>> results = new ArrayList<>();for (File file : files)//遍歷給定目錄中的所有文件//如果是文件夾if (file.isDirectory()){//遞歸MatchCounter counter = new MatchCounter(file, keyword, pool);Future<Integer> result = pool.submit(counter);results.add(result);}//如果是文件，則調用search()方法 看是否包含關鍵字。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;}}}
4.2 主程序
public class ThreadPoolTest{public static void main(String[] args) throws Exception{try (Scanner in = new Scanner(System.in)){System.out.print("請輸入要查找的目錄：");String directory = in.nextLine();System.out.print("請輸入要查找的關鍵字：");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("線程池最大數量 =" + largestPoolSize);}}}
4.3 運行結果：
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