Java中的Runnable、Callable、Future、FutureTask的區別與示例

原文地址：http://blog.csdn.net/bboyfeiyu/article/details/24851847

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Java中存在Runnable、Callable、Future、FutureTask這幾個與線程相關的類或者接口，在Java中也是比較重要的幾個概念，我們通過下面的簡單示例來了解一下它們的作用于區別。

Runnable

其中Runnable應該是我們最熟悉的接口，它只有一個run()函數，用于將耗時操作寫在其中，該函數沒有返回值。然后使用某個線程去執行該runnable即可實現多線程，Thread類在調用start()函數后就是執行的是Runnable的run()函數。Runnable的聲明如下 :?

[java]?view plaincopy  
 public?interface?Runnable?{??
 ????/**?
 ?????*?When?an?object?implementing?interface?<code>Runnable</code>?is?used?
 ?????*?to?create?a?thread,?starting?the?thread?causes?the?object's?
 ?????*?<code>run</code>?method?to?be?called?in?that?separately?executing?
 ?????*?thread.?
 ?????*?<p>?
 ?????*?
 ?????*?@see?????java.lang.Thread#run()?
 ?????*/??
 ????public?abstract?void?run();??
 }??

Callable

Callable與Runnable的功能大致相似，Callable中有一個call()函數，但是call()函數有返回值，而Runnable的run()函數不能將結果返回給客戶程序。Callable的聲明如下 :

[java]?view plaincopy  
 public?interface?Callable<V>?{??
 ????/**?
 ?????*?Computes?a?result,?or?throws?an?exception?if?unable?to?do?so.?
 ?????*?
 ?????*?@return?computed?result?
 ?????*?@throws?Exception?if?unable?to?compute?a?result?
 ?????*/??
 ????V?call()?throws?Exception;??
 }??

可以看到，這是一個泛型接口，call()函數返回的類型就是客戶程序傳遞進來的V類型。

Future

Executor就是Runnable和Callable的調度容器，Future就是對于具體的Runnable或者Callable任務的執行結果進行

取消、查詢是否完成、獲取結果、設置結果操作。get方法會阻塞，直到任務返回結果(Future簡介)。Future聲明如下 :

[java]?view plaincopy  
 /**?
 *?@see?FutureTask?
 ?*?@see?Executor?
 ?*?@since?1.5?
 ?*?@author?Doug?Lea?
 ?*?@param?<V>?The?result?type?returned?by?this?Future's?<tt>get</tt>?method?
 ?*/??
 public?interface?Future<V>?{??
 ??
 ????/**?
 ?????*?Attempts?to?cancel?execution?of?this?task.??This?attempt?will?
 ?????*?fail?if?the?task?has?already?completed,?has?already?been?cancelled,?
 ?????*?or?could?not?be?cancelled?for?some?other?reason.?If?successful,?
 ?????*?and?this?task?has?not?started?when?<tt>cancel</tt>?is?called,?
 ?????*?this?task?should?never?run.??If?the?task?has?already?started,?
 ?????*?then?the?<tt>mayInterruptIfRunning</tt>?parameter?determines?
 ?????*?whether?the?thread?executing?this?task?should?be?interrupted?in?
 ?????*?an?attempt?to?stop?the?task.?????*?
 ?????*/??
 ????boolean?cancel(boolean?mayInterruptIfRunning);??
 ??
 ????/**?
 ?????*?Returns?<tt>true</tt>?if?this?task?was?cancelled?before?it?completed?
 ?????*?normally.?
 ?????*/??
 ????boolean?isCancelled();??
 ??
 ????/**?
 ?????*?Returns?<tt>true</tt>?if?this?task?completed.?
 ?????*?
 ?????*/??
 ????boolean?isDone();??
 ??
 ????/**?
 ?????*?Waits?if?necessary?for?the?computation?to?complete,?and?then?
 ?????*?retrieves?its?result.?
 ?????*?
 ?????*?@return?the?computed?result?
 ?????*/??
 ????V?get()?throws?InterruptedException,?ExecutionException;??
 ??
 ????/**?
 ?????*?Waits?if?necessary?for?at?most?the?given?time?for?the?computation?
 ?????*?to?complete,?and?then?retrieves?its?result,?if?available.?
 ?????*?
 ?????*?@param?timeout?the?maximum?time?to?wait?
 ?????*?@param?unit?the?time?unit?of?the?timeout?argument?
 ?????*?@return?the?computed?result?
 ?????*/??
 ????V?get(long?timeout,?TimeUnit?unit)??
 ????????throws?InterruptedException,?ExecutionException,?TimeoutException;??
 }??

FutureTask

FutureTask則是一個RunnableFuture<V>，而RunnableFuture實現了Runnbale又實現了Futrue<V>這兩個接口，

[java]?view plaincopy  
 public?class?FutureTask<V>?implements?RunnableFuture<V>??

RunnableFuture

[java]?view plaincopy  
 public?interface?RunnableFuture<V>?extends?Runnable,?Future<V>?{??
 ????/**?
 ?????*?Sets?this?Future?to?the?result?of?its?computation?
 ?????*?unless?it?has?been?cancelled.?
 ?????*/??
 ????void?run();??
 }??

另外它還可以包裝Runnable和Callable<V>，由構造函數注入依賴。

[java]?view plaincopy  
 public?FutureTask(Callable<V>?callable)?{??
 ????if?(callable?==?null)??
 ????????throw?new?NullPointerException();??
 ????this.callable?=?callable;??
 ????this.state?=?NEW;???????//?ensure?visibility?of?callable??
 }??
 ??
 public?FutureTask(Runnable?runnable,?V?result)?{??
 ????this.callable?=?Executors.callable(runnable,?result);??
 ????this.state?=?NEW;???????//?ensure?visibility?of?callable??
 }??

可以看到，Runnable注入會被Executors.callable()函數轉換為Callable類型，即FutureTask最終都是執行Callable類型的任務。該適配函數的實現如下：

[java]?view plaincopy  
 public?static?<T>?Callable<T>?callable(Runnable?task,?T?result)?{??
 ????if?(task?==?null)??
 ????????throw?new?NullPointerException();??
 ????return?new?RunnableAdapter<T>(task,?result);??
 }??

RunnableAdapter適配器

[java]?view plaincopy  
 /**?
 ?*?A?callable?that?runs?given?task?and?returns?given?result?
 ?*/??
 static?final?class?RunnableAdapter<T>?implements?Callable<T>?{??
 ????final?Runnable?task;??
 ????final?T?result;??
 ????RunnableAdapter(Runnable?task,?T?result)?{??
 ????????this.task?=?task;??
 ????????this.result?=?result;??
 ????}??
 ????public?T?call()?{??
 ????????task.run();??
 ????????return?result;??
 ????}??
 }??

由于FutureTask實現了Runnable，因此它既可以通過Thread包裝來直接執行，也可以提交給ExecuteService來執行。

并且還可以直接通過get()函數獲取執行結果，該函數會阻塞，直到結果返回。因此FutureTask既是Future、

Runnable，又是包裝了Callable( 如果是Runnable最終也會被轉換為Callable )，它是這兩者的合體。

簡單示例

[java]?view plaincopy  
 ?package?com.effective.java.concurrent.task;??
 ??
 import?java.util.concurrent.Callable;??
 import?java.util.concurrent.ExecutionException;??
 import?java.util.concurrent.ExecutorService;??
 import?java.util.concurrent.Executors;??
 import?java.util.concurrent.Future;??
 import?java.util.concurrent.FutureTask;??
 ??
 /**?
 ?*??
 ?*?@author?mrsimple?
 ?*?
 ?*/??
 public?class?RunnableFutureTask?{??
 ??
 ????/**?
 ?????*?ExecutorService?
 ?????*/??
 ????static?ExecutorService?mExecutor?=?Executors.newSingleThreadExecutor();??
 ??
 ????/**?
 ?????*??
 ?????*?@param?args?
 ?????*/??
 ????public?static?void?main(String[]?args)?{??
 ????????runnableDemo();??
 ????????futureDemo();??
 ????}??
 ??
 ????/**?
 ?????*?runnable,?無返回值?
 ?????*/??
 ????static?void?runnableDemo()?{??
 ??
 ????????new?Thread(new?Runnable()?{??
 ??
 ????????????@Override??
 ????????????public?void?run()?{??
 ????????????????System.out.println("runnable?demo?:?"?+?fibc(20));??
 ????????????}??
 ????????}).start();??
 ????}??
 ??
 ????/**?
 ?????*?其中Runnable實現的是void?run()方法，無返回值；Callable實現的是?V?
 ?????*?call()方法，并且可以返回執行結果。其中Runnable可以提交給Thread來包裝下?
 ?????*?，直接啟動一個線程來執行，而Callable則一般都是提交給ExecuteService來執行。?
 ?????*/??
 ????static?void?futureDemo()?{??
 ????????try?{??
 ????????????/**?
 ?????????????*?提交runnable則沒有返回值,?future沒有數據?
 ?????????????*/??
 ????????????Future<?>?result?=?mExecutor.submit(new?Runnable()?{??
 ??
 ????????????????@Override??
 ????????????????public?void?run()?{??
 ????????????????????fibc(20);??
 ????????????????}??
 ????????????});??
 ??
 ????????????System.out.println("future?result?from?runnable?:?"?+?result.get());??
 ??
 ????????????/**?
 ?????????????*?提交Callable,?有返回值,?future中能夠獲取返回值?
 ?????????????*/??
 ????????????Future<Integer>?result2?=?mExecutor.submit(new?Callable<Integer>()?{??
 ????????????????@Override??
 ????????????????public?Integer?call()?throws?Exception?{??
 ????????????????????return?fibc(20);??
 ????????????????}??
 ????????????});??
 ??
 ????????????System.out??
 ????????????????????.println("future?result?from?callable?:?"?+?result2.get());??
 ??
 ????????????/**?
 ?????????????*?FutureTask則是一個RunnableFuture<V>，即實現了Runnbale又實現了Futrue<V>這兩個接口，?
 ?????????????*?另外它還可以包裝Runnable(實際上會轉換為Callable)和Callable?
 ?????????????*?<V>，所以一般來講是一個符合體了，它可以通過Thread包裝來直接執行，也可以提交給ExecuteService來執行?
 ?????????????*?，并且還可以通過v?get()返回執行結果，在線程體沒有執行完成的時候，主線程一直阻塞等待，執行完則直接返回結果。?
 ?????????????*/??
 ????????????FutureTask<Integer>?futureTask?=?new?FutureTask<Integer>(??
 ????????????????????new?Callable<Integer>()?{??
 ????????????????????????@Override??
 ????????????????????????public?Integer?call()?throws?Exception?{??
 ????????????????????????????return?fibc(20);??
 ????????????????????????}??
 ????????????????????});??
 ????????????//?提交futureTask??
 ????????????mExecutor.submit(futureTask)?;??
 ????????????System.out.println("future?result?from?futureTask?:?"??
 ????????????????????+?futureTask.get());??
 ??
 ????????}?catch?(InterruptedException?e)?{??
 ????????????e.printStackTrace();??
 ????????}?catch?(ExecutionException?e)?{??
 ????????????e.printStackTrace();??
 ????????}??
 ????}??
 ??
 ????/**?
 ?????*?效率底下的斐波那契數列,?耗時的操作?
 ?????*??
 ?????*?@param?num?
 ?????*?@return?
 ?????*/??
 ????static?int?fibc(int?num)?{??
 ????????if?(num?==?0)?{??
 ????????????return?0;??
 ????????}??
 ????????if?(num?==?1)?{??
 ????????????return?1;??
 ????????}??
 ????????return?fibc(num?-?1)?+?fibc(num?-?2);??
 ????}??
 ??
 }??