Activity Implementation

Activities are implemented by providing an implementation of the @Activities interface. The AWS Flow Framework for Java uses the activity implementation instances configured on the worker to process activity tasks at run time. The worker automatically looks up the activity implementation of the appropriate type.

You can use properties and fields to pass resources to activity instances, such as database connections. Since the activity implementation object may be accessed from multiple threads, shared resources must be thread safe.

Note that the activity implementation doesn't take parameters of type Promise<> or return objects of that type. This is because the implementation of the activity should not depend on how it was invoked (synchronously or asynchronously).

The activities interface shown before can be implemented like this:

public class MyActivitiesImpl implements MyActivities {

   @Override
   @ManualActivityCompletion
   public int activity1(){
      //implementation
   }

   @Override
   public void activity2(int foo){
     //implementation
   }
}    

A thread local context is available to the activity implementation that can be used to retrieve the task object, data converter object being used, etc. The current context can be accessed through ActivityExecutionContextProvider.getActivityExecutionContext(). For more details, see the AWS SDK for Java documentation for ActivityExecutionContext and the section Execution Context.

Manually Completing Activities

The @ManualActivityCompletion annotation in the example above is an optional annotation. It is allowed only on methods that implement an activity and is used to configure the activity to not automatically complete when the activity method returns. This could be useful when you want to complete the activity asynchronously—for example, manually after a human action has been completed.

By default, the framework considers the activity completed when your activity method returns. This means that the activity worker reports activity task completion to Amazon SWF and provides it with the results (if any). However, there are use cases where you don't want the activity task to be marked completed when the activity method returns. This is especially useful when you are modeling human tasks. For example, the activity method may send an email to a person who must complete some work before the activity task is completed. In such cases, you can annotate the activity method with @ManualActivityCompletion annotation to tell the activity worker that it should not complete the activity automatically. In order to complete the activity manually, you can either use the ManualActivityCompletionClient provided in the framework or use the RespondActivityTaskCompleted method on the Amazon SWF Java client provided in the Amazon SWF SDK. For more details, see the AWS SDK for Java documentation.

In order to complete the activity task, you need to provide a task token. The task token is used by Amazon SWF to uniquely identify tasks. You can access this token from the ActivityExecutionContext in your activity implementation. You must pass this token to the party that is responsible for completing the task. This token can be retrieved from the ActivityExecutionContext by calling ActivityExecutionContextProvider.getActivityExecutionContext().getTaskToken().

The getName activity of the Hello World example can be implemented to send an email asking someone to provide a greeting message:

@ManualActivityCompletion
@Override
public String getName() throws InterruptedException {
    ActivityExecutionContext executionContext
         = contextProvider.getActivityExecutionContext();
    String taskToken = executionContext.getTaskToken();
    sendEmail("[e-mail]",
         "Please provide a name for the greeting message and close task with token: " + taskToken);
    return "This will not be returned to the caller";
}

The following code snippet can be used to provide the greeting and close the task by using the ManualActivityCompletionClient. Alternatively, you can also fail the task:

public class CompleteActivityTask {

    public void completeGetNameActivity(String taskToken) {

        AmazonSimpleWorkflow swfClient
           = new AmazonSimpleWorkflowClient(...); // use AWS access keys
        ManualActivityCompletionClientFactory manualCompletionClientFactory
           = new ManualActivityCompletionClientFactoryImpl(swfClient);
        ManualActivityCompletionClient manualCompletionClient
           = manualCompletionClientFactory.getClient(taskToken);
        String result = "Hello World!";
        manualCompletionClient.complete(result);
    }

    public void failGetNameActivity(String taskToken, Throwable failure) {
        AmazonSimpleWorkflow swfClient
           = new AmazonSimpleWorkflowClient(...); // use AWS access keys
        ManualActivityCompletionClientFactory manualCompletionClientFactory
           = new ManualActivityCompletionClientFactoryImpl(swfClient);
        ManualActivityCompletionClient manualCompletionClient
           = manualCompletionClientFactory.getClient(taskToken);
        manualCompletionClient.fail(failure);
    }
}