前言
Future是一个接口类，定义了5个方法：
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
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。
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：
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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