Question

如何在java中获取线程异步执行之后的结果

Answer 1

java中提供了Future<V>接口和实现了Future接口的FutureTask<V> 类来将线程执行之后的结果返回（通过get()方法）。
1.Future<V>接口
Runnable接口执行任务是不返回任何值的，Runnable的run()方法的执行结果是void,而Future接口的call方法是有返回结果的，这是Runnable跟Future的区别之一，它们的另一个不同之处就是实现了Runnable接口的任务执行是调用ExecutorService的execute(Runnable task)方法，而实现了Future接口的任务是调用ExecutorService的submit(Future task)方法。调用Future的get()方法就能直接得到任务的返回值，该方法会一直阻塞直到任务的结果出来为止，我们可以调用Future的isDone()方法来判断该任务的结果是否准备就绪。
[java] view plain copy
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
public class TestFuture {
public static void main(String[] args) throws InterruptedException, ExecutionException {
ExecutorService executor = Executors.newCachedThreadPool();
Future result1 = executor.submit(new Callable() {
@Override
public Integer call() throws Exception {
int sum = 0;
for (int i = 0; i < 10; i++) {
sum += i;
}
return sum;
}
});
Future result2 = executor.submit(new Callable() {
@Override
public Integer call() throws Exception {
int sum = 0;
for (int i = 10; i < 100; i++) {
sum += i;
}
return sum;
}
});
executor.shutdown();
System.out.println(result1.get() + result2.get());
}
}
2.FutureTask类
FutureTask实现了Future接口，将一个Callable实例作为参数传给它，就能创建一个FutureTask实例，然后用ExecutorService的submit方法来执行这个实例。最后同样是用get方法获取线程执行后的结果。
[plain] view plain copy
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.FutureTask;
public class TestFutureTask {
public static void main(String[] args) throws InterruptedException, ExecutionException {
ExecutorService executor = Executors.newCachedThreadPool();
Callable task = new Callable() {
@Override
public String call() throws Exception {
return "结果";
}
};
FutureTask ft = new FutureTask(task);
executor.submit(ft);
System.out.println(ft.get());
executor.shutdown();
}
}empty