Java中的Callable和Future的使用和困惑
Java中的Callable和Future的使用和困惑
Java中还提供了可以返回值的线程池,例子如下:
[java]- 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 CallableAndFuture {
- /**
- * @param args
- */
- public static void main(String[] args) {
- ExecutorService threadPool = Executors.newSingleThreadExecutor();
- Future<String> future = threadPool.submit(new Callable<String>(){
- @Override
- public String call() throws Exception {
- Thread.sleep(3000);
- return "future";
- }
- });
- try {
- System.out.println("waiting...");
- System.out.println(future.get());
- } catch (InterruptedException e) {
- e.printStackTrace();
- } catch (ExecutionException e) {
- e.printStackTrace();
- }
- }
- }
future.get()结果出来之前,要等待一会
future.get(300, TimeUnit.MILLISECONDS);然而这个如果在规定的时间内没有完成,则停止,并且跑出超时异常
还有需要注意的地方,Callable中的泛型和call方法的类型一直,并且还要和Future的泛型类型一致。
下面的例子是,可以返回多个Future对象
[java]- //创建线程池
- ExecutorService pool = Executors.newFixedThreadPool(10);
- //创建CompletionService实例
- CompletionService<Integer> completionService = new ExecutorCompletionService<Integer>(pool);
- //提交任务
- for(int i = 0;i < 10; i++){
- final int index = i;
- completionService.submit(new Callable<Integer>(){
- @Override
- public Integer call() throws Exception {
- return index;
- }
- });
- }
- //获得结果
- for(int i = 0;i<10;i++){
- try {
- Future<Integer> future2 = completionService.take();
- System.out.println(future2.get());
- } catch (InterruptedException e) {
- e.printStackTrace();
- } catch (ExecutionException e) {
- e.printStackTrace();
- }
- }
- }
不知道用在什么地方,业务需求没有碰到过这种情况
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