前言
Future是一个接口类，定义了5个方法：
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boolean cancel( boolean mayInterruptIfRunning); boolean isCancelled(); boolean isDone(); V get() throws InterruptedException, ExecutionException; V get( long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException; |
通过这5个方法可以看出，Future不但可以获取提交任务的执行结果，甚至还可以取消任务。
Future使用示例
摘自JDK中Future示例代码
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class ArchiveSearcherImpl implements ArchiveSearcher{
@Override public String search(String target) { try { Thread.sleep( 1000 ); } catch (InterruptedException e) { e.printStackTrace(); } return target; } }
interface ArchiveSearcher { String search(String target); }
class App {
public static void main(String[] args) throws InterruptedException { App app = new App(); app.showSearch( "search" ); }
ExecutorService executor = Executors.newSingleThreadExecutor(); ArchiveSearcher searcher = new ArchiveSearcherImpl();
void showSearch( final String target) throws InterruptedException { // 提交任务 Future<String> future = executor.submit( new Callable<String>() { public String call() { return searcher.search(target); } }); displayOtherThings(); // do other things while searching try { // 拿任务执行结果 displayText(future.get()); // use future } catch (ExecutionException ex) { //cleanup(); return ; } } private void displayOtherThings() { System.out.println( "do other things" ); }
private void displayText(String s) { System.out.println(s); } } |
注意： future.get() 方法是阻塞式的，如果调用该方法的时候任务尚未执行完成，则会一直等待下去，直到任务执行结束。
ExecutorService还有一个sumbit方法比较特殊： <T> Future<T> submit(Runnable task, T result); 这个方法可以先把result这个参数传给task使用，然后再通过get方法把result返回。
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public class FutureTest {
public static void main(String[] args) throws ExecutionException, InterruptedException { ExecutorService executor = Executors.newSingleThreadExecutor();
MyResult myResult = new MyResult(); MyTask myTask = new MyTask(myResult);
// 提交任务后，在任务中操作myResult Future<MyResult> future = executor.submit(myTask, myResult); // 最后get方法可以拿到myResult System.out.println(future.get()); }
}
class MyTask implements Runnable {
private MyResult myResult;
public MyTask(MyResult myResult) { this .myResult = myResult; }
@Override public void run() { myResult.setCode( "10000" ); } }
@Data @ToString class MyResult { private String code; } |
FutureTask
FutureTask是一个实现了Runnable和Future接口的工具类，结合了这两个接口的能力，FutureTask即可以提交给线程任务执行，又可以获取到执行结果。
具体代码示例：
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import java.util.concurrent.*;
public class FutureTaskTest {
public static void main(String[] args) throws ExecutionException, InterruptedException { FutureTask<String> futureTask1 = new FutureTask<>( new MyTask1()); FutureTask<String> futureTask2 = new FutureTask<>( new MyTask2());
ExecutorService executorService = Executors.newFixedThreadPool( 2 ); executorService.submit(futureTask1); executorService.submit(futureTask2);
long start = System.currentTimeMillis(); System.out.println(futureTask1.get()); System.out.println(futureTask2.get()); long end = System.currentTimeMillis();
System.out.println(end - start); }
}
class MyTask2 implements Callable<String> {
@Override public String call() { try { Thread.sleep( 2000 ); } catch (InterruptedException e) { e.printStackTrace(); } return "MyTask2 over" ; } }
class MyTask1 implements Callable<String> {
@Override public String call() { try { Thread.sleep( 1000 ); } catch (InterruptedException e) { e.printStackTrace(); } return "MyTask1 over" ; } } |
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原文链接：https://blog.csdn.net/CSDN_WYL2016/article/details/125093947
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