Future接口是Java標(biāo)準(zhǔn)API的一部分，在java.util.concurrent包中。Future接口是Java線(xiàn)程Future模式的實(shí)現(xiàn)，可以來(lái)進(jìn)行異步計(jì)算。
有了Future就可以進(jìn)行三段式的編程了，1.啟動(dòng)多線(xiàn)程任務(wù)2.處理其他事3.收集多線(xiàn)程任務(wù)結(jié)果。從而實(shí)現(xiàn)了非阻塞的任務(wù)調(diào)用。在途中遇到一個(gè)問(wèn)題，那就是雖然能異步獲取結(jié)果，但是Future的結(jié)果需要通過(guò)isdone來(lái)判斷是否有結(jié)果，或者使用get()函數(shù)來(lái)阻塞式獲取執(zhí)行結(jié)果。這樣就不能實(shí)時(shí)跟蹤其他線(xiàn)程的結(jié)果狀態(tài)了，所以直接使用get還是要慎用，最好配合isdone來(lái)使用。
這里有一種更好的方式來(lái)實(shí)現(xiàn)對(duì)任意一個(gè)線(xiàn)程運(yùn)行完成后的結(jié)果都能及時(shí)獲取的辦法：使用CompletionService，它內(nèi)部添加了阻塞隊(duì)列，從而獲取future中的值，然后根據(jù)返回值做對(duì)應(yīng)的處理。一般future使用和CompletionService使用的兩個(gè)測(cè)試案例如下：
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import java.util.ArrayList;import java.util.List;import java.util.Random;import java.util.concurrent.Callable;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import java.util.concurrent.Future;/** * 多線(xiàn)程執(zhí)行，異步獲取結(jié)果 * * @author i-clarechen * */public class AsyncThread { public static void main(String[] args) { AsyncThread t = new AsyncThread(); List<Future<String>> futureList = new ArrayList<Future<String>>(); t.generate(3, futureList); t.doOtherThings(); t.getResult(futureList); } /** * 生成指定數(shù)量的線(xiàn)程，都放入future數(shù)組 * * @param threadNum * @param fList */ public void generate(int threadNum, List<Future<String>> fList) { ExecutorService service = Executors.newFixedThreadPool(threadNum); for (int i = 0; i < threadNum; i++) { Future<String> f = service.submit(getJob(i)); fList.add(f); } service.shutdown(); } /** * other things */ public void doOtherThings() { try { for (int i = 0; i < 3; i++) { System.out.println("do thing no:" + i); Thread.sleep(1000 * (new Random().nextInt(10))); } } catch (InterruptedException e) { e.printStackTrace(); } } /** * 從future中獲取線(xiàn)程結(jié)果，打印結(jié)果 * * @param fList */ public void getResult(List<Future<String>> fList) { ExecutorService service = Executors.newSingleThreadExecutor(); service.execute(getCollectJob(fList)); service.shutdown(); } /** * 生成指定序號(hào)的線(xiàn)程對(duì)象 * * @param i * @return */ public Callable<String> getJob(final int i) { final int time = new Random().nextInt(10); return new Callable<String>() { @Override public String call() throws Exception { Thread.sleep(1000 * time); return "thread-" + i; } }; } /** * 生成結(jié)果收集線(xiàn)程對(duì)象 * * @param fList * @return */ public Runnable getCollectJob(final List<Future<String>> fList) { return new Runnable() { public void run() { for (Future<String> future : fList) { try { while (true) { if (future.isDone() && !future.isCancelled()) { System.out.println("Future:" + future + ",Result:" + future.get()); break; } else { Thread.sleep(1000); } } } catch (Exception e) { e.printStackTrace(); } } } }; }} |
運(yùn)行結(jié)果打印和future放入列表時(shí)的順序一致，為0，1，2：
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do thing no:0do thing no:1do thing no:2Future:java.util.concurrent.FutureTask@68e1ca74,Result:thread-0Future:java.util.concurrent.FutureTask@3fb2bb77,Result:thread-1Future:java.util.concurrent.FutureTask@6f31a24c,Result:thread-2 |
下面是先執(zhí)行完的線(xiàn)程先處理的方案：
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import java.util.Random;import java.util.concurrent.BlockingQueue;import java.util.concurrent.Callable;import java.util.concurrent.CompletionService;import java.util.concurrent.ExecutionException;import java.util.concurrent.ExecutorCompletionService;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import java.util.concurrent.Future;import java.util.concurrent.LinkedBlockingDeque;public class testCallable { public static void main(String[] args) { try { completionServiceCount(); } catch (InterruptedException e) { e.printStackTrace(); } catch (ExecutionException e) { e.printStackTrace(); } } /** * 使用completionService收集callable結(jié)果 * @throws ExecutionException * @throws InterruptedException */ public static void completionServiceCount() throws InterruptedException, ExecutionException { ExecutorService executorService = Executors.newCachedThreadPool(); CompletionService<Integer> completionService = new ExecutorCompletionService<Integer>( executorService); int threadNum = 5; for (int i = 0; i < threadNum; i++) { completionService.submit(getTask(i)); } int sum = 0; int temp = 0; for(int i=0;i<threadNum;i++){ temp = completionService.take().get(); sum += temp; System.out.print(temp + "\t"); } System.out.println("CompletionService all is : " + sum); executorService.shutdown(); } public static Callable<Integer> getTask(final int no) { final Random rand = new Random(); Callable<Integer> task = new Callable<Integer>() { @Override public Integer call() throws Exception { int time = rand.nextInt(100)*100; System.out.println("thead:"+no+" time is:"+time); Thread.sleep(time); return no; } }; return task; }} |
運(yùn)行結(jié)果為最先結(jié)束的線(xiàn)程結(jié)果先被處理：
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thead:0 time is:4200thead:1 time is:6900thead:2 time is:2900thead:3 time is:9000thead:4 time is:7100 0 1 4 3 CompletionService all is : 10 |
總結(jié)
以上就是本文關(guān)于Java利用future及時(shí)獲取線(xiàn)程運(yùn)行結(jié)果的全部?jī)?nèi)容，希望對(duì)大家有所幫助。有什么問(wèn)題可以隨時(shí)留言，歡迎大家交流討論。
原文鏈接：http://www.cnblogs.com/clarechen/p/4604189.html
