14.Java中的Future模式

ExecutorService executor = Executors.newSingleThreadExecutor();
Future<String> future = executor.submit(callable);    //主线程需要callable线程的结果，先拿到一个未来的Future
System.out.println(future.get());    //有了结果后再根据get方法取真实的结果,当然如果此时callable线程如果没有执行完get方法会阻塞执行完，如果执行完则直接返回结果或抛出异常

1 package com.future;
2 
3 /**
4  * 数据结果
5  * Created by yulinfeng on 6/18/17.
6  */
7 public interface Data {
8     String getResult() throws InterruptedException;
9 }

 1 package com.future;
 2 
 3 /**
 4  * 结果的真实计算过程
 5  * Created by yulinfeng on 6/18/17.
 6  */
 7 public class RealData implements Data {
 8     protected String data;
 9 
10     public RealData(String data) {
11         try {
12             System.out.println("正在计算结果");
13             Thread.sleep(3000);     //模拟计算
14         } catch (InterruptedException e) {
15             e.printStackTrace();
16         }
17         this.data = data + “ world”;
18     }
19 
20     public String getResult() throws InterruptedException {
21         return data;
22     }
23 }

 1 package com.future;
 2 
 3 /**
 4  * 真实结果RealData的代理
 5  * Created by yulinfeng on 6/18/17.
 6  */
 7 public class FutureData implements Data {
 8     RealData realData = null;   //对RealData的封装，代理了RealData
 9     boolean isReady = false;    //真实结果是否已经准备好
10 
11     public synchronized void setResultData(RealData realData) {
12         if (isReady) {
13             return;
14         }
15         this.realData = realData;
16         isReady = true;
17         notifyAll();    //realData已经被注入到了futureData中，通知getResult方法
18     }
19 
20     public synchronized String getResult() throws InterruptedException {
21         if (!isReady) {
22             wait();     //数据还未计算好，阻塞等待
23         }
24         return realData.getResult();
25     }
26 }

 1 package com.future;
 2 
 3 /**
 4  * Client主要完成的功能包括：1. 返回一个FutureData；2.开启一个线程用于构造RealData
 5  * Created by yulinfeng on 6/18/17.
 6  */
 7 public class Client {
 8 
 9     public Data request(final String string) {
10         final FutureData futureData = new FutureData();
11 
12         /*计算过程比较慢，单独放到一个线程中去*/
13         new Thread(new Runnable() {
14 
15             public void run() {
16                 RealData realData = new RealData(string);
17                 futureData.setResultData(realData);
18             }
19         }).start();
20 
21         return futureData;  //先返回一个“假”的futureData
22     }
23 }

 1 /**
 2  * 负责调用Client发起请求，并使用返回的数据。
 3  * Created by yulinfeng on 6/18/17.
 4  */
 5 public class Main {
 6     public static void main(String[] args) throws InterruptedException {
 7         Client client = new Client();
 8         System.out.println("准备计算结果");
 9         Data data = client.request("hello");    //立即返回一个“假”的futureData，可以不用阻塞的等待数据返回，转而执行其它任务
10         System.out.println("执行其它任务");
11         Thread.sleep(3000);     //模拟执行其它任务
12         System.out.println("数据的计算结果为：" + data.getResult());
13     }
14 }

 1 package com.future;
 2 
 3 import java.util.concurrent.Callable;
 4 
 5 /**
 6  * 结果的真实计算过程
 7  * Created by yulinfeng on 6/18/17.
 8  */
 9 public class RealData2 implements Callable<String> {
10     protected String data;
11 
12     public RealData2(String data) {
13         this.data = data;
14     }
15     public String call() throws Exception {
16         try {
17             System.out.println("正在计算结果");
18             Thread.sleep(2000);     //模拟计算结果
19         } catch (InterruptedException e) {
20             e.printStackTrace();
21         }
22         this.data = data + " world";
23         return data;
24     }
25 }

 1 package com.future;
 2 
 3 import java.util.concurrent.ExecutionException;
 4 import java.util.concurrent.ExecutorService;
 5 import java.util.concurrent.Executors;
 6 import java.util.concurrent.Future;
 7 
 8 /**
 9  * 负责调用Executor的submit，并使用返回的数据。
10  * Created by yulinfeng on 6/18/17.
11  */
12 public class Main2 {
13 
14     public static void main(String[] args) throws InterruptedException, ExecutionException {
15         ExecutorService client = Executors.newSingleThreadExecutor();   //类似Client
16         System.out.println("准备计算结果");
17         Future<String> data = client.submit(new RealData2("hello"));    //类似Client.request
18         System.out.println("执行其它任务");
19         Thread.sleep(3000);
20         System.out.println("数据的计算结果为：" + data.get());
21     }
22 }

//ThreadPoolExecutor$Worker#runWorker
task.run();