10.Callable与Future的应用

import java.util.Random;
import java.util.concurrent.Callable;
import java.util.concurrent.CompletionService;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorCompletionService;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

/**
* Callable与Future的应用
* Future取得的结果类型和Callable返回的结果类型必须一致，这是通过泛型来实现。
* Callable要采用ExecutorService的submit方法提交，返回的future对象可以取消任务。
* CompletionService用于提交一组Callable任务，其take方法返回已完成的一个Callable任务对应的Future对象。
* @author LiTaiQing
*
*/
public class CallableAndFuture {

public static void main(String[] args) {

ExecutorService threadPool = Executors.newSingleThreadExecutor();
Future<String> future =
//有返回结果时用submit
threadPool.submit(new Callable<String>(){
@Override
public String call() throws Exception {
return "Hello";
}

});

System.out.println("等待结果");
try {
System.out.println("拿到结果" + future.get());
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}

ExecutorService threadPool2 = Executors.newFixedThreadPool(10);
CompletionService<Integer> completionService = new ExecutorCompletionService<Integer>(threadPool2);
for(int i = 1; i < 10; i++){
final int seq = i;
completionService.submit(new Callable<Integer>(){
@Override
public Integer call() throws Exception {
Thread.sleep(new Random().nextInt(5000));
return seq;
}

});
}

for(int i = 0 ; i < 10; i++){
try {
System.out.println(completionService.take().get());
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
};
}

}

}