多线程处理中Future的妙用

java 中Future是一个未来对象，里面保存这线程处理结果，它像一个提货凭证，拿着它你可以随时去提取结果。在两种情况下，离开Future几乎很难办。一种情况是拆分订单，比如你的应用收到一个批量订单，此时如果要求最快的处理订单，那么需要并发处理，并发的结果如果收集，这个问题如果自己去编程将非常繁琐，此时可以使用CompletionService解决这个问题。CompletionService将Future收集到一个队列里，可以按结果处理完成的先后顺序进队。另外一种情况是，如果你需要并发去查询一些东西（比如爬虫），并发查询只要有一个结果返回，你就认为查询到了，并且结束查询，这时也需要用CompletionService和Future来解决。直接上代码更直观：

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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.CompletionService; import java.util.concurrent.ExecutorCompletionService; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Future;   public class CompletionServiceTest {           static int numThread =100;     static ExecutorService executor = Executors.newFixedThreadPool(numThread);       public static void main(String[] args) throws Exception{         //data表示批量任务         int[] data =new int[100];         for(int i=1;i<100000;i++){             int idx =i % 100;             data[idx] =i;             if(i%100==0){                 testCompletionService(data);                 data =new int[100];             }         }     }           private static void testCompletionService(int [] data) throws Exception{                CompletionService<Object> ecs = new ExecutorCompletionService<Object>(executor);         for(int i=0;i<data.length;i++){             final Integer t=data[i];             ecs.submit(new Callable<Object>() {                 public Object call() {                     try {                         Thread.sleep(new Random().nextInt(1000));                     } catch (InterruptedException e) {                         e.printStackTrace();                     }                     return t;                 }             });         }         //CompletionService会按处理完后顺序返回结果         List<Object> res =new ArrayList<Object>();         for(int i = 0;i<data.length;i++ ){             Future<Object> f = ecs.take();             res.add(f.get());         }                       System.out.println(Thread.currentThread().getName()+":"+res);     }           private static void testBasicFuture(int [] data) throws Exception{              List<Future<Object>> res =new ArrayList<Future<Object>>();         for(int i=0;i<data.length;i++){             final Integer t=data[i];             Future<Object> future=executor.submit(new Callable<Object>() {                 public Object call() {                     return t;                 }             });             res.add(future);         }                         for(int i = 0;i<res.size();i++ ){             Future<Object> f = res.get(i);             Object rObject =f.get();             System.out.print(":"+rObject);         }                       System.out.println("LN");     } }