HelloWorldWorkflowAsync Application

Sometimes, it's preferable to have a workflow perform certain tasks locally instead of using an activity. However, workflow tasks often involve processing the values represented by Promise<T> objects. If you pass a Promise<T> object to a synchronous workflow method, the method executes immediately but it can't access the Promise<T> object's value until the object is ready. You could poll Promise<T>.isReady until it returns true, but that's inefficient and the method might block for a long time. A better approach is to use an asynchronous method.

An asynchronous method is implemented much like a standard method—often as a member of the workflow implementation class—and runs in the workflow implementation's context. You designate it as an asynchronous method by applying an @Asynchronous annotation, which directs the framework to treat it much like an activity.

This topic is a walkthrough of HelloWorldWorkflowAsync, a modified version of HelloWorldWorkflow that replaces one of the activities with an asynchronous method. To implement the application, create a copy of the helloWorld.HelloWorldWorkflow package in your project directory and name it helloWorld.HelloWorldWorkflowAsync.

The following sections describe how to modify the original HelloWorldWorkflow code to use an asynchronous method.

HelloWorldWorkflowAsync Activities Implementation

HelloWorldWorkflowAsync implements its activities worker interface in GreeterActivities, as follows:

import com.amazonaws.services.simpleworkflow.flow.annotations.Activities;
import com.amazonaws.services.simpleworkflow.flow.annotations.ActivityRegistrationOptions;

@Activities(version="2.0")
@ActivityRegistrationOptions(defaultTaskScheduleToStartTimeoutSeconds = 300,
                             defaultTaskStartToCloseTimeoutSeconds = 10)
public interface GreeterActivities {
   public String getName();
   public void say(String what);
}

This interface is similar to the one used by HelloWorldWorkflow, with the following exceptions:

The remaining activity method implementations are identical to HelloWorldWorkflow. Just delete getGreeting from GreeterActivitiesImpl.

HelloWorldWorkflowAsync Workflow Implementation

HelloWorldWorkflowAsync defines the workflow interface as follows:

import com.amazonaws.services.simpleworkflow.flow.annotations.Execute;
import com.amazonaws.services.simpleworkflow.flow.annotations.Workflow;
import com.amazonaws.services.simpleworkflow.flow.annotations.WorkflowRegistrationOptions;

@Workflow
@WorkflowRegistrationOptions(defaultExecutionStartToCloseTimeoutSeconds = 3600)
public interface GreeterWorkflow {

   @Execute(version = "2.0")
   public void greet();
}

The interface is identical to HelloWorldWorkflow apart from a new version number. As with activities, if you want to change a registered workflow, you must change its version.

HelloWorldWorkflowAsync implements the workflow as follows:

import com.amazonaws.services.simpleworkflow.flow.annotations.Asynchronous;
import com.amazonaws.services.simpleworkflow.flow.core.Promise;

public class GreeterWorkflowImpl implements GreeterWorkflow {
   private GreeterActivitiesClient operations = new GreeterActivitiesClientImpl();

   @Override
   public void greet() {
      Promise<String> name = operations.getName();
      Promise<String> greeting = getGreeting(name);
      operations.say(greeting);
   }

   @Asynchronous
   private Promise<String> getGreeting(Promise<String> name) {
      String returnString = "Hello " + name.get() + "!";
      return Promise.asPromise(returnString);
   }
}

HelloWorldWorkflowAsync replaces the getGreeting activity with a getGreeting asynchronous method but the greet method works in much the same way:

The difference is that, instead of calling the activities client to execute a getGreeting activity, greet calls the asynchronous getGreeting method. The net result is the same, but the getGreeting method works somewhat differently than the getGreeting activity.

getGreeting creates a return value by passing the greeting string to the static Promise.asPromise method. This method creates a Promise<T> object of the appropriate type, sets the value, and puts it in the ready state.

HelloWorldWorkflowAsync Workflow and Activities Host and Starter

HelloWorldWorkflowAsync implements GreeterWorker as the host class for the workflow and activity implementations. It is identical to the HelloWorldWorkflow implementation except for the taskListToPoll name, which is set to "HelloWorldAsyncList".

import com.amazonaws.ClientConfiguration;
import com.amazonaws.auth.AWSCredentials;
import com.amazonaws.auth.BasicAWSCredentials;
import com.amazonaws.services.simpleworkflow.AmazonSimpleWorkflow;
import com.amazonaws.services.simpleworkflow.AmazonSimpleWorkflowClient;
import com.amazonaws.services.simpleworkflow.flow.ActivityWorker;
import com.amazonaws.services.simpleworkflow.flow.WorkflowWorker;

public class GreeterWorker {
    public static void main(String[] args) throws Exception {
        ClientConfiguration config = new ClientConfiguration().withSocketTimeout(70*1000);

        String swfAccessId = System.getenv("AWS_ACCESS_KEY_ID");
        String swfSecretKey = System.getenv("AWS_SECRET_KEY");
        AWSCredentials awsCredentials = new BasicAWSCredentials(swfAccessId, swfSecretKey);

        AmazonSimpleWorkflow service = new AmazonSimpleWorkflowClient(awsCredentials, config);
        service.setEndpoint("https://swf.us-east-1.amazonaws.com");

        String domain = "helloWorldWalkthrough";
        String taskListToPoll = "HelloWorldAsyncList";

        ActivityWorker aw = new ActivityWorker(service, domain, taskListToPoll);
        aw.addActivitiesImplementation(new GreeterActivitiesImpl());
        aw.start();

        WorkflowWorker wfw = new WorkflowWorker(service, domain, taskListToPoll);
        wfw.addWorkflowImplementationType(GreeterWorkflowImpl.class);
        wfw.start();
    }
}

HelloWorldWorkflowAsync implements the workflow starter in GreeterMain; it is identical to the HelloWorldWorkflow implementation.

To execute the workflow, run GreeterWorker and GreeterMain, just as with HelloWorldWorkflow.