Java: ExecutorService错误

Question

我对ExecutorService有点陌生，我对它有一个问题。我有一节课：

      @Override
      public void updateAvatar(final MultipartFile multipartFile, final String speakerId) {

        final GridFS avatarGfs = new GridFS(getTemplate().getDb(), SPEAKER_AVATAR_COLLECTION);

        // Remove all sizes
        avatarGfs.remove(new BasicDBObject(SPEAKER_ID_FIELD, speakerId));
        System.out.println("hello from updateAvatar");

        ExecutorService executorService = Executors.newFixedThreadPool(3);
        executorService.execute(new Runnable() {
          public void run() {
            for (SpeakerAvatarSize size : SpeakerAvatarSize.values()) {
              try {

                System.out.println("calling saveAvatar");
                saveAvatar(multipartFile, speakerId, size, avatarGfs);

              } catch (IOException e) {

                LOG.error("SpeakerRepository#updateAvatar", e);
              }
            }
          }
        });

        executorService.shutdown();
        System.out.println("shut down threads");
      }

在编辑当前的用户化身时，以及添加另一个化身时，我都会得到这个错误。似乎只增加了一个化身：

Exception in thread "pool-2-thread-1" java.lang.IllegalStateException: File has been moved - cannot be read again
    at org.springframework.web.multipart.commons.CommonsMultipartFile.getInputStream(CommonsMultipartFile.java:123)
    at util.ImageScaleUtil.scale(ImageScaleUtil.java:26)
    at impl.SpeakerRepository.saveAvatar(SpeakerRepository.java:97)
    at impl.SpeakerRepository.access$000(SpeakerRepository.java:28)
    at impl.SpeakerRepository$1.run(SpeakerRepository.java:81)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:745)

提前谢谢你！

Answer 1

您使用executor服务，因此saveAvatar函数可能会在updateAvater完成后运行。那时，web框架可能已经清理了multipartFile。

要等待执行程序服务，只需添加：

executorService.shutdown();
System.out.println("shut down threads");
try {
    executorService.awaitTermination(60, TimeUnit.SECONDS);
} catch (InterruptedException ignored) {
}

顺便说一句，您可以在每个查询中创建一个包含3个线程的executor服务，并且只使用其中的一个线程。由于您必须等待任务完成，所以在那里使用executor服务是没有意义的。

@Override
public void updateAvatar(final MultipartFile multipartFile, final String speakerId) {

  final GridFS avatarGfs = new GridFS(getTemplate().getDb(), SPEAKER_AVATAR_COLLECTION);

  // Remove all sizes
  avatarGfs.remove(new BasicDBObject(SPEAKER_ID_FIELD, speakerId));
  System.out.println("hello from updateAvatar");

  for (SpeakerAvatarSize size : SpeakerAvatarSize.values()) {
    try {
      System.out.println("calling saveAvatar");
      saveAvatar(multipartFile, speakerId, size, avatarGfs);
    } catch (IOException e) {

      LOG.error("SpeakerRepository#updateAvatar", e);
    }
  }
}

或者，如果希望for循环并行运行，则可以使用this answer。

@Override
public void updateAvatar(final MultipartFile multipartFile, final String speakerId) {

  final GridFS avatarGfs = new GridFS(getTemplate().getDb(), SPEAKER_AVATAR_COLLECTION);

  // Remove all sizes
  avatarGfs.remove(new BasicDBObject(SPEAKER_ID_FIELD, speakerId));
  System.out.println("hello from updateAvatar");

  Parallel.For(SpeakerAvatarSize.values(), size -> {
    try {
      System.out.println("calling saveAvatar");
      saveAvatar(multipartFile, speakerId, size, avatarGfs);
    } catch (IOException e) {
      LOG.error("SpeakerRepository#updateAvatar", e);
    }
  });
}