java 多線程，及獲取線程執行結果

Thread、Runnable 建立多線程

new Thread(new Runnable() {
           public void run() {
               System.out.println("hello");
           }
 }).start();

---

FutureTask 獲取線程執行結果

FutureTask futureTask = new FutureTask(new Callable() {
	public Object call() throws Exception {
	    return "hello";
	}
});
new Thread(futureTask).start();
String res = (String)futureTask.get();// block

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ExecutorService 更簡便的獲取線程執行結果方式

ExecutorService executorService = Executors.newSingleThreadExecutor();
Future<String> future = executorService.submit(new Callable<String>() {
	public String call() throws Exception {
	    return "hello";
	}
});
String res = future.get();

---

ThreadPoolExecutor 線程池

多線程缺點：頻繁建立、銷燬線程

線程池：封裝任務，加入線程池執行，線程可重複使用。

// 多線程
for (int i=0; i<5; i++) {
	new Thread(new Runnable() {
	    public void run() {
	        System.out.println("hello ");
	    }
	}).start();
}

// 自定義線程池
public static ThreadPoolExecutor getThreadPool(int queueSize, int multi) {
    int cpuNum = Runtime.getRuntime().availableProcessors();
    queueSize = queueSize == 0 ? cpuNum*10 : queueSize;
    ArrayBlockingQueue jobs = new ArrayBlockingQueue(queueSize);
    ThreadPoolExecutor executor = new ThreadPoolExecutor(cpuNum*multi, cpuNum*5, 5, TimeUnit.SECONDS, jobs);

    executor.allowCoreThreadTimeOut(true);// will shutdown if no task arrive within the keep-alive time
    return executor;
}

---

jdk 自帶的 Executors 類封裝了一些經常使用線程池，方便快速建立。

Executor框架包括：線程池，Executor，Executors，ExecutorService，CompletionService，Future，Callable等。

ps:

多線程和 CountDownLatch 使用。

jdk 自帶工具 jconsole 可查看 vm 狀態。

int taskNum = 20;
final CountDownLatch latch = new CountDownLatch(taskNum);// 初始化任務總數
for (int i=0; i<taskNum; i++) {
    final int tmp = i;
    new Thread(new Runnable() {
        public void run() {
            System.out.println("hello "+tmp);
            latch.countDown();// 完成一個任務，計數器減一
        }
    }).start();
}

try {
    latch.await();// 阻塞到全部任務完成
    System.out.println("finish...");
} catch (InterruptedException e) {
    e.printStackTrace();
}

---

jdk 8 中 CompletableFuture 能夠實現異步回調，而不是 Future 的阻塞、輪詢。

http://www.tuicool.com/articles/UVrMNrN

參考：

http://blog.csdn.net/ns_code/article/details/17465497

http://blog.csdn.net/ghsau/article/details/7451464