java - SWF : End workflow based on Promise

Question

我有一个调用 Activity 的决策程序。该 Activity 返回验证错误列表。如果决策者收到该列表并且它不为空，我想退出工作流。

要退出工作流程，我可以在决策程序中返回，它会退出工作流程。问题是我无法从 Activity 中获得结果。我原以为这会起作用，但它不会.. violations.isReady() 总是返回 false:

public class WorkflowImpl implements Workflow {
    ActivitiesClient activities;

    public Workflow(/*...*/) {
        // ...
    }

    @Override
    public void do(WorkflowInput input) {
        Promise<List<String>> violations = activities.validate(input);

        if (!violations.isReady()) { // "do()" will be called when violations is ready.. right?
            return;
        } else if (!CollectionUtils.isEmpty(violations.get())) {
            return; // or throw ValidationException
        }

        // do other stuff
    }
}

我不想做替代方案，即轮询 violations.isReady() 是否为真，因为这会占用决策者线程，谁知道会占用多长时间。我什至不确定这是否可行。

帮忙吗？

Answer 1

工作流代码是异步的。所以一个Promise从 Activity 返回的内容永远不会在同一个回调 中准备就绪。所以在你的代码中 violations.isReady() 总是返回 false 是正确的行为。您必须使用注释为 @Asynchronous 或 Task 的方法将 回调 关联到 Promise。所以你的代码应该是这样的:

public class WorkflowImpl implements Workflow {
  ActivitiesClient activities;

  public Workflow(/*...*/) {
      // ...
  }

  @Override
  public void do(WorkflowInput input) {
    Promise<List<String>> violations = activities.validate(input);
    processValidationResult(violations);
  }

  @Asynchronous
  private void processValidationResult(Promise<List<String>> violations) {
    // As method is @Asynchronous framework guarantees violations is ready 
    // when its body is executed.
    if (!CollectionUtils.isEmpty(violations.get())) {
        return; // or throw ValidationException
    }
    // do other stuff
  }
}

注意 AspectJ should be configured correctly使用 Flow Framework Aspects 使 @Asynchronous 注释生效。

另一种选择是直接使用任务:

public class WorkflowImpl implements Workflow {
  ActivitiesClient activities;

  public Workflow(/*...*/) {
      // ...
  }

  @Override
  public void do(WorkflowInput input) {
    Promise<List<String>> violations = activities.validate(input);
    new Task(violations) {
       @Override
       public void  doExecute() {
         // Framework guarantees violations is ready 
         // (as it is Task constructor parameter)
         // when execute method is executed.
         if (!CollectionUtils.isEmpty(violations.get())) {
             return; // or throw ValidationException
         }
         // do other stuff
       }
    };
  }
}

我建议通读 SWF Recipes和 samples更好地了解编写 SWF 工作流时使用的模式。

还要确保你通过了TryCatchFinally javadoc作为 AWS Flow Framework 错误处理虽然非常强大，但与大多数人习惯的完全不同。

添加以显示从 processValidationResult(...) 返回值的示例:

  @Override
  public void do(WorkflowInput input) {
    Promise<List<String>> violations = activities.validate(input);
    Promise<String> whatever = processValidationResult(violations);
    processNextStep(whatever);
  }

  @Asynchronous
  private Promise<String> processValidationResult(Promise<List<String>> violations) {
    // As method is @Asynchronous framework guarantees violations is ready 
    // when its body is executed.
    if (!CollectionUtils.isEmpty(violations.get())) {
        throw new ValidationException(...);
    }
    // do other stuff
    return Promise.asPromise("result string");
  }

  @Asynchronous
  private void processNextStep(Promise<String> whatever) {
     ...
  }